ToxSci Advance Access originally published online on May 28, 2003
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Toxicological Sciences 74, 393-406 (2003)
Copyright © 2003 by the Society of Toxicology
REPRODUCTIVE AND DEVELOPMENTAL TOXICOLOGY |
Effects of in Utero Exposure to Finasteride on Androgen-Dependent Reproductive Development in the Male Rat
CIIT Centers for Health Research, Research Triangle Park, North Carolina 27709
Received February 28, 2003; accepted April 21, 2003
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Finasteride is a specific inhibitor of type II 5
-reductase, the enzyme that converts testosterone (T) to the more potent androgen receptor agonist dihydrotestosterone (DHT). In utero exposure to androgen receptor antagonists and T biosynthesis inhibitors have induced permanent effects on androgen-sensitive end points such as anogenital distance (AGD), nipple retention, and malformations of the male rat reproductive tract. The objectives of this study were to (1) characterize the dose response of finasteride-mediated alterations in androgen-dependent developmental end points, (2) determine whether prenatal exposure to finasteride permanently decreases AGD or results in nipple retention, and (3) evaluate whether AGD or nipple retention is predictive of adverse alterations in the male reproductive tract. Pregnant Crl:CD(SD)BR rats (n = 5–6/group) were gavaged with either vehicle or finasteride at 0.01, 0.1, 1.0, 10, or 100 mg/kg/day on gestation days 12 to 21. All male offspring were monitored individually until necropsy on postnatal day (PND) 90. The present study design has been used previously for other antiandrogens and is sensitive to perturbations of the male rat reproductive tract. Decreases in AGD on PND 1 and increases in areolae-nipple retention on PND 13 were significantly different from controls in all finasteride-exposed male rats. Finasteride-induced changes in AGD and nipple retention were permanent in male rats exposed to finasteride at and above 0.1 mg/kg/day. On PND 90, dorsolateral and ventral prostate lobes were absent in 21 to 24% of rats exposed to 100 mg/kg/day finasteride and weighed significantly less at and above 10 mg/kg/day. In the highest dose group, 73% of animals had ectopic testes, much higher than previously reported. The most sensitive malformation other than decreased AGD and nipple retention was the dose-dependent increase in hypospadias. The lowest observed adverse effect level (LOAEL) for finasteride-induced permanent effects in this study was 0.1 mg/kg/day based on permanent changes in AGD and nipple retention. Finasteride-induced changes in AGD and retention of nipples were highly predictive of hypospadias, ectopic testes, and prostate malformations even though some animals with retained nipples or decreased AGD may not have had other reproductive tract malformations. In summary, prenatal exposure to finasteride specifically inhibited DHT-mediated development with little to no change in T-mediated development. Key Words: finasteride; 5a-reductase; development; dihydrotestosterone; in utero exposure; antiandrogen.
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Androgen production (both testosterone [T] and dihydrotestosterone [DHT]) during gestation is critical for normal male reproductive development. T is necessary for stabilization and differentiation of the Wolffian ducts into epididymides, vasa deferentia, and seminal vesicles and also for normal development of the fetal testes; DHT, produced locally from testosterone, is required for normal development of the genital tubercle and urogenital sinus into the external genitalia and prostate (Berman et al., 1995
; Clark et al., 1993; Imperato-McGinley et al., 1985; Veyssiere et al., 1982; Wilson and Lasnitzki, 1971). During development, androgens stimulate the growth of the perineal region between the sex papilla and the anus, resulting in an increased anogenital distance (AGD) in male offspring. Nipple regression in male rats is also androgen-dependent, since it requires the local production of DHT (Imperato-McGinley et al., 1986; Kratochwil, 1977). In male rats exposed in utero to antiandrogens with multiple mechanisms of action, decreased AGD and increased nipple retention have been associated with perturbation of androgen-mediated development of the reproductive tract (Clark et al., 1990; Gray et al., 1999b; Imperato-McGinley et al., 1986; McIntyre et al., 2000, 2001; Ostby et al., 1999).
In utero exposure to the antiandrogens vinclozolin, di(n-butyl) phthalate (DBP), linuron, and flutamide results in permanent external changes in phenotype (e.g., decreased AGD, increased nipple retention, hypospadias) coupled with internal male reproductive tract malformations and undescended testes (Barlow et al., 2002; Gray et al., 1999a; McIntyre et al., 2000, 2001, 2002; Mylchreest et al., 1999, 2000). Although the effects noted are similar, DBP is an inhibitor of fetal testosterone biosynthesis, whereas vinclozolin, linuron, and flutamide are competitive androgen receptor antagonists. The design used in the studies mentioned above for flutamide, linuron, and DBP has demonstrated exquisite sensitivity and robustness for evaluating effects on male reproductive development (Barlow et al., 2002; McIntyre et al., 2000, 2001, 2002; Mylchreest et al., 1999, 2000).
Finasteride is a specific inhibitor of type II 5-reductase, the enzyme that catalyzes the conversion from T to the more potent androgen receptor agonist DHT. Finasteride is currently approved for the therapeutic treatment of benign prostatic hyperplasia and male androgenic alopecia (Medical Economics Company, 2002). Pre- or postnatal exposure to finasteride has been shown to alter male reproductive development and function (Clark et al., 1990, 1993; George et al., 1989; Imperato-McGinley et al., 1992; Spencer et al., 1991). The threshold for malformations reported for in utero exposure to finasteride is 0.1 mg/kg/day based on a single animal with hypospadias (Clark et al., 1990). Decreased prostate and seminal vesicle weights, as well as minimal effects on testicular descent, have also been reported following in utero exposure to finasteride (Clark et al., 1993; Imperato-McGinley et al., 1992; Spencer et al., 1991). In male rats exposed in utero to finasteride, decreased AGD and increased nipple retention were observed in early postnatal life but were considered transient effects since they were no longer apparent in rats that had reached sexual maturity (Clark et al., 1990, 1993). The finasteride data (Clark et al., 1990) contrast with data from other antiandrogens, demonstrating that in utero exposure leads to permanent alterations in AGD and nipple retention.
The rationale for this work is that no single study has fully investigated the dose response of androgen-dependent reproductive and developmental effects following in utero exposure to finasteride. By using the same study design known to be sensitive to the adverse effects of other antiandrogens, we can evaluate if in utero exposure to finasteride induces permanently decreased AGD and increased nipple retention and whether these end points are predictive of malformations in DHT-mediated development. The objectives of this study were to (1) characterize the dose response of alterations in androgen-dependent end points following in utero exposure to finasteride, (2) determine whether prenatal exposure to finasteride permanently decreases AGD or results in nipple retention, and (3) evaluate whether AGD or nipple retention is predictive of adverse alterations in the male reproductive tract. As expected, in utero exposure to finasteride induced alterations in DHT-mediated development but not T-mediated development. Finasteride exposure induced significant and permanent decreases in AGD and increases in nipple retention. By uniquely identifying male rats at birth, early postnatal alterations (AGD and nipples) were shown to be sensitive predictors of malformations in DHT-dependent tissues that were present later in life.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Animals.
This study was conducted in accordance with Federal guidelines for the care and use of laboratory animals (National Research Council, 1996
) and was approved by the Institutional Animal Care and Use Committee at the CIIT Centers for Health Research (CIIT). Time-mated, 8- to 10-week-old, nulliparous CRL:CD(SD)BR rats were obtained from Charles River Laboratories Inc. (Raleigh, NC) on gestation day (GD) 0. GD 0 was defined as the day sperm was found in the vagina of the mated female. Animal allocation to treatment groups was done by body weight randomization to ensure unbiased weight distribution among groups. Animals were housed in the CIIT animal care facility, which is accredited by the Association for Assessment and Accreditation of Laboratory Animal Care, International. Animals were kept in a HEPA-filtered, mass air-displacement room with a 12-h, light-dark cycle at 18–26°C and relative humidity of 30–70%. Animals had access to deionized water and rodent chow ad libitum (NIH-07, Zeigler Brothers, Gardner, PA). Individual dams and offspring were housed in polycarbonate cages on ALPHA-dri bedding (Shepherd Specialty Papers, Kalamazoo, MI) until weaning on PND 21, at which time all male littermates were ear-tagged and housed by litter in groups of up to four per cage. Female offspring were euthanized by CO2 asphyxiation and aortic transection on PND 22 and were not subjected to a detailed postmortem examination. On PND 45, all male littermates were separated into two or three per cage until necropsy.
Treatment.
Sperm-positive animals, 5–6 dams per dose group, were gavaged daily (between 8 and 9 A.M.) from GD 12 to 21 with corn oil (Sigma Chemical Company, St. Louis, MO) containing 15% ethanol (2 ml/kg/day) or finasteride (>99% purity, Apin Chemical Ltd, Oxford, UK) at 0.01, 0.1, 1.0, 10, and 100 mg/kg/day (2 ml/kg/day) dissolved in 15% ethanol/corn oil (vol/vol). Dose levels chosen for this study were based on previous studies that set a threshold of response to finasteride at 0.1 mg/kg/day based on the threshold induction of hypospadias and a 100% incidence of hypospadias at 100 mg/kg/day (Clark et al., 1990). Dams were examined twice daily for clinical signs of toxicity. Dam body weights were recorded daily prior to dosing and weekly during lactation. Dam food consumption was monitored weekly throughout dosing and lactation.
Androgen-dependent reproductive end points.
On the day of delivery, which was considered to be PND 1, pups were counted and examined for clinical signs of toxicity. Pups were uniquely identified by foot tattoo, and AGD was measured using a dissecting microscope with an eyepiece reticle. A single investigator unaware of the exposure group of the animals performed all AGD measurements. Definitive sex of all offspring was determined by PND 21. Pup litter weights (by sex) and individual pup weights were collected on PND 1. Pup litter weights were also collected on PND 4, 7, 14, and 21. At weaning (PND 21), male offspring were ear-tagged, and individual body weights were recorded weekly.
Male pups were inspected for the presence and number of areolae and nipples on PND 13. Since no distinction was made between the retention of an areola or nipple on PND 13, this structure was referred to as an areola-nipple. A single investigator unaware of the exposure group of the animal recorded the number and location of areolae-nipples. All male offspring were examined for preputial separation, testicular descent, and malformations of the external genitalia beginning on PND 38.
Necropsy of dams.
Male pups were weaned on PND 21, and dams were euthanized by CO2 asphyxiation and aortic transection. Body and organ weights (liver, kidneys, and uterus) and number of implantion sites were recorded.
Necropsy of F1 males.
Sexually mature (PND 93–105) male rats were euthanized by decapitation, and trunk blood was collected. An external examination of the scrotum, prepuce, and penis was conducted on all animals. The ventral thorax and abdomen were shaved on all animals for counting nipples, and the AGD was measured with a dial caliper. Body weight and the following organ weights were collected: liver, kidneys, adrenal glands, testes, epididymides, ventral prostate lobes, dorsolateral prostate lobes, seminal vesicles (with coagulating glands and seminal fluid), levator ani bulbocavernosous (LABC) muscle, and bulbourethral glands. Tissues were fixed in modified Davidson’s fixative (testes and epididymides only) (Latendresse et al., 2002) or 10% neutral-buffered formalin, processed, embedded in paraffin, sectioned at 5 µm, and stained with hematoxylin and eosin. Histopathology was performed on control and 100 mg/kg/day dose groups. Since there were absent prostate lobes from animals in the 100 mg/kg/day dose group and a high incidence of prostatic hypoplasia, dorsolateral and ventral prostate lobes of the 10 mg/kg/day dose group were also examined histologically. Since nothing remarkable was observed in the histopathology of the remaining tissues from animals in the high-dose group, the histopathology of these tissues was not evaluated in the lower dose groups.
Dose response curves.
For AGD and areola-nipple retention, a female AGD (1.83 mm, determined from study controls on PND 1) and 12 nipples per rat were considered maximal (100%) responses on PND 1 and 13 respectively. Changes in AGD, areola-nipple retention, and organ weights are represented as percentage difference (absolute) from control. Malformation responses (unilateral or bilateral ectopic testes, hypospadias, and organ agenesis) are presented as individual incidences. Curves were generated by Sigma Plot (version 7.0, SPSS, Inc., Richmond, CA).
Statistical analysis.
Statistical analyses were conducted using JMP (version 4.0.4, SAS Institute, Cary, NC). Normality and homogeneity of variances were evaluated prior to data analysis. Since the proportion of pups born alive, pups surviving to weaning, and sex ratio were not normally distributed, an arcsine transformation was conducted prior to analysis. Pup data were nested by dam to yield litter means for analysis. Multivariate analysis of variance was used for bodyweight data, and either analysis of variance or analysis of covariance was used to test for significance of treatment effects with covariates defined in figure legends. If the p value for treatment effects was less than 0.05, contrasts of least square means were used to assess the significance of treatment differences. Since the number of nipples per rat was not normally distributed and is a noncontinuous variable, the relationship between retained nipples on PND 13 and PND 90 was determined by contingency analysis followed by the Cochran-Mantel-Haenszel test. The significance (p < 0.05) of gross lesions in finasteride-exposed groups compared to the control group was determined using the Fisher’s Exact Test. To determine whether finasteride-mediated decreases in AGD on PND 1 were associated with malformations of androgen-dependent tissues in adult animals, logistic regressions were performed and were considered significant if the model fit was significant (p < 0.05). After logistic regression, the Receiver Operator Characteristic (ROC) and inverse prediction functions were used. ROC is a graphic display that gives a measure of the predictive accuracy of the logistic regression model and is presented as area under the curve (AUC). AUC values approaching 1.0 are fully predictive, whereas values approaching 0.5 are not (Hanley and McNeil, 1982). The inverse prediction function of the logistic regression analysis was used to predict the AGD (and the respective confidence intervals) at which 10 and 50% of the pups would display a given malformation.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Effects of Finasteride Exposure on Pregnancy and Reproductive Performance
While dam body weight and food consumption were not altered by finasteride, body weight gain during treatment (GD 12–21) was significantly decreased in the 0.1 and 100 mg/kg/day dose groups by 16 and 21%, respectively, but not in the 0.01, 1, or 10 mg/kg/day dose groups (Table 1
). All dams were pregnant and littered normally, although one dam in the 0.1 mg/kg/day dose group cannibalized her offspring within 24 h. There was no statistical difference in length of gestation with finasteride, although average gestational length was 0.6 days longer in dams dosed with 100 mg/kg/day compared to dams in the other dose groups (data not shown). Organ weights (liver, kidney, and uterus) of finasteride-exposed dams were not significantly different from control dams (Table 1).
|
Reproductive performance was not significantly altered in dams exposed to finasteride during late gestation (Table 2
). The number of live pups born per litter and the number of implantion sites were not significantly altered by finasteride exposure, indicating that immediate cannabalization of neonates in the one litter at 0.1 mg/kg/day was not related to exposure. The proportion of pups born alive and surviving to weaning was not significantly affected by finasteride exposure, although there was a small decrease in pup survival in the 0.1 mg/kg/day dose group as a result of the one litter that was cannibalized in that group. In utero exposure to finasteride did not alter sex ratio, litter size, or male pup body weight at PND 1, 21, or 90 (Table 2). There were also no effects of finasteride on weekly pup body weights taken between PND 21 and necropsy (data not shown).
|
Effects of Finasteride Exposure on Postnatal End Points
Late gestational exposure to finasteride significantly decreased AGD of male offspring in a dose-responsive manner. On PND 1, the AGD of male offspring displayed significant decreases of 8, 16, 23, 25, and 33% in the 0.01, 0.1, 1.0, 10, and 100 mg/kg/day dose groups, respectively (Fig. 1A
, black bars). The mean AGD for control female pups on PND 1 was 1.83 mm ± 0.04 mm (SE) (Fig. 1B, dotted line). The AGD measured in sexually mature male offspring (PND 90) was decreased 2, 6, 9, 12, and 20% in the 0.01, 0.1, 1.0, 10, and 100 mg/kg/day dose groups, respectively (Fig. 1A, white bars). Permanent decreases in AGD were significantly different from the controls in the 0.1 mg/kg/day dose group and above (with body weight used as a covariate). The adjusted AGD (using body weight as a covariate) of all males on PND 1 displayed a normal distribution (Fig. 1B). AGD on PND 1 was plotted against AGD on PND 90 for each individual animal (Fig. 1C) in order to illustrate that the finasteride-induced decreases in AGD showed good consistency within the individual animals of each dose group across the time course of the study.
|
In utero exposure to finasteride induced a dose-dependent increase in the mean number of areolae-nipples retained in male rats. On PND 13, these animals displayed a mean number of 0.1, 0.9, 3.7, 6.1, 8.4, and 11.4 areolae-nipples per rat in the 0, 0.01, 0.1, 1.0, 10, and 100 mg/kg/day dose groups, respectively (Fig. 2A
, black bars). This increase in retained areolae-nipples on PND 13 was significant in all finasteride dose groups. Vehicle-control pups on PND 13 had observable areolae-nipples (1 and 3) in only 2 out of 33 control animals (6%), while areolae-nipples were observed in 22 out of 23 pups (95.7%) on PND 13 in the 0.1 mg/kg/day dose group. Prenatal exposure to 1, 10, and 100 mg/kg/day finasteride resulted in 100% of pups displaying areolae-nipples on PND 13 (Fig. 2B). At a dose level of 100 mg/kg/day, 23 out of 33 pups (70%) displayed a fully feminized areolae phenotype on PND 13 with 12 areolae-nipples per male pup (Fig. 2B). In most cases (31/33) there was a clear absence of areolae-nipples in control pups compared to finasteride-exposed pups (Figs. 3A and 3B, respectively).
|
|
At necropsy on PND 90, the ventral abdomen and thorax of all adult male rats were shaved and inspected for retention of nipples (Fig. 3C,D
). These male rats exhibited a mean number of 0.1, 0.3, 2.5, 3.7, 6.5, and 9.1 nipples per rat in the 0, 0.01, 0.1, 1.0, 10, and 100 mg/kg/day finasteride dose groups, respectively (Fig. 2A, white bars). Increased retention of nipples on PND 90 was significant in the 0.1 mg/kg/day dose group and above. On PND 90, only 2 out of 33 control animals (6%) displayed 1 and 2 nipples, respectively. In the 10 mg/kg/day dose group 28 out of 31 animals (90%) exhibited 6 or more retained nipples (Fig. 2B). On PND 90 in the 100 mg/kg/day dose group, 5 out of 33 animals (15%) exhibited a fully feminized phenotype of 12 nipples, and 12 out of 33 animals (36%) had 10–11 nipples. Retained nipples on PND 90 were observed in 100% of the animals exposed in utero to 10 and 100 mg/kg/day finasteride (Fig. 2B). Contingency analysis of the number of nipples on PND 13 versus PND 90 and subsequent Cochran-Mantel-Haenszel test (blocked for dose) indicated a significant linear association between these two time points. Evaluation of prenatal finasteride exposure on the onset of puberty, as determined by complete separation of the prepuce from the ventral surface of the glands penis, was precluded by the presence of hypospadias in the top three dose groups. A cleft prepuce was observed in all finasteride-exposed animals from PND 38 to 55, with severity increasing with dose group. In the animals without hypospadias, there was a slight but nonsignificant dose-dependent delay in preputial separation, the time separating the average dates of preputial separation between the animals in the control group and the 10 mg/kg/day dose group was 0.91 days (data not shown).
Adverse Finasteride-Mediated Lesions Observed at Necropsy
In utero exposure to finasteride induced marked malformations of the male reproductive tract (Table 3). Of the rats in the 1.0 mg/kg/day dose group, 30% displayed hypospadias. No hypospadias were observed in the 0, 0.01, or 0.1 mg/kg/day dose groups, but incidences of hypospadias were 30, 48, and 88% in the 1, 10, and 100 mg/kg/day dose groups, respectively. Compared to controls (Fig. 4A), penises with hypospadias had incomplete closure of the urethral folds on the ventral surface resulting in an ectopic urethal opening (Fig. 4B). A frenulum of tissue often extended to the glans causing ventral curvature of the penis.
|
|
Prenatal finasteride exposure significantly impaired testicular descent. Approximately 3, 23, and 73% of the adult males displayed ectopic testes in the 1.0, 10, and 100 mg/kg/day dose groups, respectively (Fig. 5
and Table 3). In all animals with unilateral and bilateral maldescent, ectopic testes had descended through the inguinal canal and were located in the subcutis of the inguinal area rather than descending into the scrotum (Fig. 3C). All ectopic testes and epididymides were hypoplastic. Organ weights for ectopic testes and epididymides were significantly lower than in control animals. There was no significant change in organ weights of normally descended testes and epididymides from finasteride-exposed rats (Table 4).
|
|
Both ventral and dorsolateral prostate lobes were affected in a dose-responsive manner by in utero exposure to finasteride (Table 4
). Hypoplastic ventral and dorsolateral prostate lobes were observed in all groups at necropsy, but the incidence was significantly higher in the 10 and 100 mg/kg/day dose groups, with 65 to 70% of animals affected in both groups (Table 3). The increased incidence of hypoplastic prostate lobes was consistent with the decreased organ weights of ventral (23 and 44%) and dorsolateral (19 and 33%) prostate lobes in the 10 and 100 mg/kg/day dose groups, respectively (Table 4). Histologically, the epithelium lining the glands in affected rats appeared similar to controls, and there were fewer lobules. In the 100 mg/kg/day exposure group, 21% (7/33) and 24% (8/33) of animals had no ventral or dorsolateral prostate, respectively (Table 3). The dorsolateral prostate and ventral prostate lobes were at the base of the seminal vesicle in control animals (Fig. 4C) but absent in some high-dose animals (Fig. 4D). When the presence or absence of the dorsolateral prostate was difficult to determine during the gross examination, prostatic lobe and seminal vesicle weights were not collected for that animal. The absence of the dorsolateral or ventral prostates was confirmed histologically. Prenatal exposure to finasteride also resulted in a 24% lower seminal vesicle weights in the 100 mg/kg/day dose group.
In the 10 and 100 mg/kg/day dose groups, in utero exposure to finasteride resulted in 23% (4/5 of the litters) and 61% (6/6 of the litters) of the animals with either unilateral or bilateral absence of bulbourethral glands (Table 3, Fig. 4F). At the highest dose, the weights of the bulbourethral glands were significantly lower than controls (Table 4). The decreased weight of the LABC was significant in the 1.0 mg/kg/day dose group and above (Table 4). Compared to controls, the bulbocavernosous muscle was markedly underdeveloped and was accompanied by a smaller levator ani (Fig. 4E and 4F). In utero exposure to finasteride did not affect weights of the liver, kidneys, or adrenal glands (Table 4).
Dose-Response Relationships Among Markers of Altered Androgen-Mediated Development
The dose-response curves for finasteride-induced malformations fell into two groups (Fig. 6A and 6B). External structural changes such as decreased AGD on PND 1 and increased nipple retention on PND 13 and 90 had similar dose-response curves. These external changes were almost linear over the entire dose range (0.01 to 100 mg/kg/day) and approached 100% incidence by the highest dose (Fig. 6A). Starting at 1.0 mg/kg/day, the incidence of hypospadias was intermediate to the other curves in Figure 6A and the responses in Figure 6B. Other malformations such as ectopic testes and absent bulbourethal glands had similar dose-response curves with significant effects in the 10 and 100 mg/kg/day dose groups (Fig. 6B). The incidence of absent prostates was similar between ventral and dorsolateral lobes, exhibiting a 21 to 24% response, but was observed only in the 100 mg/kg/day dose group (Fig. 6B).
|
Dose-response curves for androgen-dependent organ weights following in utero exposure to finasteride were different for tissues developmentally dependent on DHT or T (Figs. 6C and 6D
, respectively). For purposes of comparison to the rest of Figure 6, decreased organ weights are presented as the percentage response relative to control (e.g. a decreased weight is shown as an increased response). The curves for decreased weights of bulbourethral glands, LABC, and ventral and dorsolateral prostate lobes were similar. For these DHT-dependent tissues, prenatal exposure to finasteride induced a dose-dependent increase in the percentage of the response, starting with the lowest dose group (0.01 mg/kg/day), and reached a maximum of 50% in the highest dose group (Fig. 6C). There were negligible effects on the weights of the seminal vesicles (although significant at 100 mg/kg/day finasteride) and no effects on the weights of descended testes and epididymides at the dose levels evaluated in this study (Fig. 6D).
The Association of AGD or Nipple Retention with Male Reproductive Tract Malformations
Logistic regression was used to evaluate the association between decreases in AGD on PND 1 and subsequent malformations in androgen-dependent tissues following in utero exposure to finasteride. In this study a malformation is defined as a rare structural alteration that has been found to be permanent. The absence or presence of a malformation in a respective tissue versus the AGD of that same animal on PND 1 was found to be significant (p < 0.05) for all malformations evaluated (nipple retention, hypospadias, ectopic testes, absent bulbourethral glands, or absent prostates). The ROC analysis of this regression and corresponding AUC values for each malformation, all over 0.9, indicate that AGD on PND 1 predicts subsequent malformations (Table 5). The utilization of the inverse prediction function calculated the AGD at which 50% or 10% of the animals would display the corresponding malformation (Table 5). The predicted AGD at which 50 and 10% of the animals would have hypospadias was determined to be 2.39 and 2.50 mm, respectively. In contrast, the predicted AGD where 50 and 10% of the animals would have absent prostates was 1.87 and 2.16 mm, respectively. Since the mean female AGD was 1.83 mm, a nearly feminized AGD in male pups would be necessary to have 50% of adult animals with missing prostates. In addition, based on this model the normal range of control male AGD values on PND 1 (2.80 to 3.35 mm with a mean of 3.13 mm) would predict a low incidence of areolae-nipples on PND 13 and nipples on PND 90 in control animals.
|
Adult male rats with malformations displayed a variable number of nipples (Fig. 7
). An increase in the number of nipples was correlated with an increased incidence of hypospadias. The presence of 10 to 12 nipples was associated with 83 to 93% incidence of hypospadias. The curves representing the relationship between increasing numbers of permanent nipples and the increased incidence of ectopic testes and bulbourethral gland agenesis were very similar. In contrast, a nearly feminized phenotype of 10–12 nipples was required for a 20% incidence of absent prostates.
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Male rat offspring exposed to finasteride from GD 12 to 21 (the critical window of male reproductive tract development) were uniquely identified at birth, and various androgen-dependent developmental end points were evaluated throughout life. Other than a slight decrease in maternal weight gain during dosing, no adverse effects on the dam or reproductive performance were observed. In utero exposure to finasteride induced significant dose-dependent alterations of DHT-mediated development with minimal affects on T-mediated development. Prenatal finasteride exposure led to a significant and permanent decrease in AGD, increase in nipple retention, and a high incidence of ectopic testes, which has not been previously reported. AGD on PND 1 was shown to be a sensitive predictor of malformations that were present in sexually mature animals. The data presented here demonstrate that finasteride-induced effects on male reproductive development were consistent with the effects of other types of antiandrogens (AR-antagonists and a T-biosynthesis inhibitor) evaluated using a similar study design and dosing regime (Barlow et al., 2002
; McIntyre et al., 2000, 2001, 2002; Mylchreest et al., 1999, 2000).
Permanence of AGD and Retained Nipples
Late gestational exposure to antiandrogens, including finasteride, decreases AGD and increases nipple retention in male rat pups (Clark et al., 1990; Gray et al., 1999a,b, 2000; Hellwig et al., 2000; Imperato-McGinley et al., 1986, 1992; McIntyre et al., 2001, 2002; Mylchreest et al., 1999, 2000). The persistence of these effects in sexually mature animals has been shown with multiple AR antagonists (Gray et al., 1999a; McIntyre et al., 2001, 2002) and an inhibitor of steroid biosynthesis (Barlow et al., 2002). The possible exception to this trend has been finasteride (Clark et al., 1990). In a previous report on prenatal exposure to finasteride, the authors concluded that decreased AGD was partially reversible postnatally (Clark et al., 1990). The authors also reported that the recovery of decreased AGD was essentially complete in the 0.1 mg/kg/day group by PND 140 (Clark et al., 1990). In contrast, we demonstrated a permanent decrease in AGD (PND 90) in the 0.1 mg/kg/day dose group and above (Fig. 1A). The lack of a no observed effect level (NOEL) on PND 1 AGD in the current study was consistent with a decreased AGD on PND 1 at doses down to 0.003 mg/kg/day finasteride (Clark et al., 1990). In the current study, the AGD measurements were taken on the same animal on PND 1 and 90, which enabled a direct comparison between measurements (Fig. 1C). The question of permanently decreased AGD in antiandrogen-exposed neonatal and adult male rats may result from catch-up growth of the perineum, as described by Clark et al. (1990). This catch-up growth occurs following cessation of exposure postnatally to the antiandrogen resulting in less dramatic changes in the AGD of sexually mature animals. This likely explains why the significant decrease in AGD on PND 1 observed in the 0.01 mg/kg/day dose group was no longer significant on PND 90.
In utero exposure to flutamide, linuron, vinclozolin, and di(n-butyl) phthalate all resulted in permanent nipple retention (Barlow et al., 2002; Gray et al., 1999a; McIntyre et al., 2001, 2002). In the current study, retention of areolae-nipples was significant in all exposure groups (down to 0.01 mg/kg/day) on PND 13, and the persistence of these nipples on PND 90 was significant in the 0.1 mg/kg/day dose group and above (Fig. 2A). These data are not consistent with a previous report on prenatal exposure to finasteride, in which no nipples were observed in male rats on PND 11 at dosages of 0.1 mg/kg/day or less (Clark et al., 1990). In addition, the authors also reported that the presence of nipples was transient, since they were no longer apparent after the animals reached sexual maturity (Clark et al., 1990). Presence of permanent nipples in adult animals exposed in utero to finasteride has been noted in a previous study (Imperato-McGinley et al., 1992). If the adult rats were not shaved, determining the presence or absence of nipples would be difficult. No mention of shaving animals was described in the previous study where no permanent nipples were observed (Clark et al., 1990). Similar to percent decrease in AGD, the number of retained nipples decreases between initial observations in early postnatal life and those made in sexually mature animals.
Finasteride-Induced Effects on the Male Reproductive Tract
The increased incidence of hypospadias following in utero exposure to finasteride is well documented (Clark et al., 1990; Imperato-McGinley et al., 1992). A dose-dependent increase in hypospadias with an incidence of 33% in the 1.0 mg/kg/day dose group and 88% in the highest dose group was observed in the current study. These data are consistent with the threshold for finasteride-induced effects in rats set at 0.1 mg/kg/day based on the single occurrence of a hypospadia in this dose group (Clark et al., 1990). Furthermore, Clark et al. also demonstrated a dose-related increase in incidence of hypospadias that almost attained a 100% incidence in the 100 mg/kg/day dose group. These results are consistent with a previous study where hypospadias were present in male rats exposed in utero to 25 mg/kg/day through to 320 mg/kg/day finasteride (Imperato-McGinley et al., 1992).
Prenatal exposure to finasteride induced a dose-dependent increase in the incidence of ectopic testes with a single occurrence in the 1 mg/kg/day dose group and 73% of individuals affected in the 100 mg/kg/day dose group (Fig. 5). The high incidence of testicular maldescent in this study was an unexpected observation, since previous studies using similar dosing windows found little to no effect on testicular descent (Clark et al., 1990) and others reported a relatively low incidence of undescended testes (8 to 27%) (Imperato-McGinley et al., 1992; Spencer et al., 1991). A possible explanation for the discrepancy between studies is the route of exposure, subcutaneous (Imperato-McGinley et al., 1992; Spencer et al., 1991) compared with gavage in the current study, or the vehicle used to deliver the drug, methyl-cellulose (Clark et al., 1990) compared with ethanol/oil used in other studies (Imperato-McGinley et al., 1992; Spencer et al., 1991) and in the current study. The gubernaculum of the GD 18 rat fetus has high 5-reductase activity, and its growth was inhibited by exposure to a 5-reductase inhibitor (George, 1989). The data from the current study suggest that the conversion of T to DHT in the developing gubernaculum is necessary for normal testicular descent.
Rat prostate development is dependent on local formation of DHT during late gestation (George and Peterson, 1988). In this study, there was also a dose-dependent decrease in prostate weights (Fig. 6C) with significant decreases in the dorsolateral and ventral prostate lobes in the 10 and 100 mg/kg/day dose groups. Furthermore, prenatal exposure to finasteride resulted in complete agenesis of the dorsolateral and ventral prostate lobes in 21 to 24% of animals in the 100 mg/kg/day dose group. Significant decreases in ventral prostate organ weights have been reported following in utero exposure to dose levels of finasteride ranging from 20 to 320 mg/kg/day (Clark et al., 1993; Imperato-McGinley et al., 1992). However, neither of these studies reported an absence of the dorsolateral and ventral lobes of the prostate. Fetal rats examined immediately following prenatal dosing with alternative 5-reductase inhibitors had impaired prostatic bud formation at 50 mg/kg/day but not at 36 mg/kg/day and below (George and Peterson, 1988; Imperato-McGinley et al., 1985). These two studies support the absence of prostates seen in adult rats following in utero exposure to 100 mg/kg/day finasteride but not at 10 mg/kg/day. The absence of prostates is not as sensitive to prenatal exposure to finasteride compared to the incidence of hypospadias, ectopic testes, and absent bulbourethral glands (Fig. 6B). This decreased comparative sensitivity of the prostate in the current study is consistent with the conclusions of Imperato-McGinley et al.(1985) that prenatal prostatic differentiation may have a much lower threshold than external structures, requiring less DHT for differentiation. Furthermore, the prostate is more dependent on postnatal DHT than either the penis or testis (George et al., 1989), suggesting that the differential sensitivity of the prostate compared with other structures may simply be due to partial perturbation during the prenatal window of exposure.
Wolffian duct differentiation into the epididymides, vasa deferentia, and seminal vesicles is T-dependent. Thus in utero exposure to finasteride was not expected to alter the development of these organs. Consistent with previous studies, prenatal exposure to finasteride did not directly affect descended testes and epididymides. Only the undescended testes and epididymides had significantly decreased organ weights compared to the controls (Table 4). The decreased weight of ectopic testes and epididymides is consistent with previous studies demonstrating the failure of spermatogenesis in undescended testes, and subsequent impairment in sperm production results in a reduction in the weights of testes and epididymides (e.g., Jegou et al., 1984). The weights of the seminal vesicles (with coagulating gland and fluid) were significantly decreased by finasteride in the 100 mg/kg/day dose group (Fig. 6D, Table 4). Animals exposed in utero to 25 mg/kg/day finasteride and higher in a previous study exhibited significantly decreased seminal vesicle weights (Imperato-McGinley et al., 1992). Pharmacological studies demonstrated that inhibition of 5-reductase activity resulted in growth inhibition of the seminal vesicles (Blohm et al., 1986). However, seminal vesicle and coagulating gland weights were not altered by prenatal exposure to 20 mg/kg/day finasteride (GD 16–17) (Clark et al., 1993). A prenatal dose greater than 20 mg/kg/day finasteride is apparently necessary to decrease the weight of seminal vesicles.
In utero exposure to finasteride decreased LABC weight in a dose-dependent manner. The shape of the dose-response curve for the effect of finasteride on LABC was similar to that observed for the prostatic lobes and bulbourethral glands (Fig. 6C). This effect on LABC weight is consistent with the effects of other antiandrogens such as flutamide, procymidone, vinclozolin, and linuron (Gray et al., 1999b; McIntyre et al., 2001; Ostby et al., 1999). These effects on organ weight are surprising since the LABC and bulbourethral glands are not thought to require DHT for pre- and postnatal growth, nor do they express 5-reductase (Blohm et al., 1986; George et al., 1989; Gloyna and Wilson, 1969). In the current study, more than one malformation was often observed in individual animals, demonstrating that in utero exposure to finasteride altered the development of several tissues that differentiate from the Wolffian ducts, urogenital sinus, and genital tubercle under the control of DHT.
The Association of AGD or Nipple Retention with Male Reproductive Tract Malformations
AGD on PND 1 was found to be highly predictive of permanent malformations of the male reproductive tract, as determined by logistic regression (Table 5). The ROC analysis and inverse prediction function demonstrated that AGD on PND 1 shows differing sensitivities in its ability to predict lesions in DHT-mediated development with prenatal exposure to finasteride. In addition, nipple retention on PND 90 was associated with an increased incidence of hypospadias, ectopic testes, and absence of prostatic lobes and bulbourethral glands in adult male rats following in utero exposure to finasteride (Fig . 7). In similar studies investigating the effects of prenatal exposure to flutamide and DBP on male reproductive development, AGD on PND 1 and nipple retention were associated with malformations in both DHT- and T-dependent tissues (N. J. Barlow, manuscript submitted; McIntyre et al., 2001). With flutamide, AGD on PND 1 and nipple retention better predicted malformations in DHT-dependent tissues than in T-dependent tissues (McIntyre et al., 2001). In contrast, DBP-induced effects on PND 1 AGD and nipple retention had a stronger relationship with malformations in T-dependent tissues than in DHT-dependent tissues (N. J. Barlow, manuscript submitted). Furthermore, although nipple retention induced by both flutamide and DBP was associated with altered T-mediated development, nipple retention by the weak AR antagonist linuron was not associated with malformations of T-dependent organs (Foster and McIntyre, 2002; McIntyre et al., 2002). Therefore the relationship between AGD, nipple retention, and male reproductive tract malformations in adult male rats following in utero exposure is strictly dependent on the potency of the antiandrogen and its mechanisms of action.
In summary, the current study demonstrated a permanent dose-dependent reduction in AGD and retention of nipples in adult male rats exposed during late gestation to finasteride. Finasteride-induced alterations were predominantly in tissues dependent on DHT during development. One unexpected observation was the high incidence of ectopic testes in finasteride-exposed males, which suggests that DHT synthesis is important for testicular descent in rodents. Changes in AGD and nipple retention were associated with increased incidence of hypospadias, ectopic testes, and absent prostatic lobes and bulbourethral glands. In this study we characterized the dose response of finasteride-induced effects on male reproductive tract development and using an experimental design that complements studies investigating the effects of flutamide, linuron, DBP, and fenitrothion (N. J. Barlow, manuscript submitted; McIntyre et al., 2001, 2002; Mychreest et al., 1999Mychreest et al., 2000; Turner et al., 2002).
|
ACKNOWLEDGMENTS |
|---|
The authors would like to thank Dr. Kevin Gaido and Dr. David C. Dorman for critical review of this manuscript, Dr. Barbara Kuyper for editorial review, and Ms. Kathy Claypoole for assistance in manuscript preparation. The authors are very grateful to Mr. Paul Ross and the animal care staff and to Ms. Elizabeth Gross-Bermudez and the necropsy and histology staff.
This work was supported by a grant from the American Chemistry Council, which does not have control over the resulting publication.
|
NOTES |
|---|
1 Present address: WIL Research Laboratories, Ashland, OH 44805.
2 Present address: Aventis Pharmaceuticals, Bridgewater, NJ 08807.
3 Present address: Merck Research Laboratories, West Point, PA 19486.
4 To whom correspondence should be addressed at National Institute of Environmental Health Sciences, P.O. Box 12233 (MD E1-06), Research Triangle Park NC 27709. Fax: (919) 541-4634. E-mail: foster2{at}niehs.nih.gov.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Barlow, N. J., McIntyre, B. S., and Foster, P. M. D. (2002). Permanent alteration of anogenital distance and nipple retention in male rats exposed to di(n-butyl) phthalate in utero. Toxicol. Sci. 66(Suppl.), 233 (Abstract).
Berman, D. M., Tian, H., and Russell, D. W. (1995). Expression and regulation of steroid 5-reductase in the urogenital tract of the fetal rat. Mol. Endocrinol. 9, 1561–1570.
Blohm, T. R., Laughlin, M. E., Benson, H. D., Johnston, J. O., Wright, C. L., Schatzman, G. L., and Weintraub, P. M. (1986). Pharmacological induction of 5-reductase deficiency in the rat: Separation of testosterone-mediated and 5-dihydrotestosterone-mediated effects. Endocrinology119, 959–966.
Clark, R. L., Anderson, C. A., Prahalada, S., Robertson, R. T., Lochry, E. A., Leonard, Y. M., Stevens, J. L., and Hoberman, A. M. (1993). Critical developmental periods for effects on male rat genitalia induced by finasteride, a 5-reductase inhibitor. Toxicol. Appl. Pharmacol. 119,34–40.[CrossRef][Web of Science][Medline]
Clark, R. L., Antonello, J. M., Grossman, S. J., Wise, L. D., Anderson, C., Bagdon, W. J., Prahalada, S., MacDonald, J. S., and Robertson, R. T. (1990). External genitalia abnormalities in male rats exposed in utero to finasteride, a 5-reductase inhibitor. Teratology 42, 91–100.[CrossRef][Web of Science][Medline]
Foster, P. M. D., and McIntyre, B. S. (2002). Endocrine active agents: Implications of adverse and non-adverse changes. Toxicol. Pathol. 30, 59–65.[CrossRef][Web of Science][Medline]
George, F. W. (1989). Developmental pattern of 5-reductase activity in the rat gubernaculum. Endocrinology124, 727–732.
George, F. W., Johnson, L., and Wilson, J. D. (1989). The effect of a 5-reductase inhibitor on androgen physiology in the immature male rat. Endocrinology 125, 2434–2438.
George, F. W., and Peterson, K. G. (1988).5-Dihydrotestosterone formation is necessary for embryogenesis of the rat prostate. Endocrinology 122, 1159–1164.
Gloyna, R. E., and Wilson, J. D. (1969). A comparative study of the conversion of testosterone to 17ß-hydroxy-5-androstan-3-one (dihydrotestosterone) by prostate and epididymis. J. Clin. Endocrinol. Metab. 29, 970–977.
Gray, L. E., Ostby, J., Furr, J., Price, M., Veeramachaneni, D. N. R., and Parks, L. (2000). Perinatal exposure to the phthalates DEHP, BBP, and DINP, but not DEP, DMP, or DOTP, alters sexual differentiation of the male rat. Toxicol. Sci. 58, 350–365.
Gray, L. E., Jr., Ostby, J., Monosson, E., and Kelce, W. R. (1999a). Environmental antiandrogens: Low doses of the fungicide vinclozolin alter sexual differentiation of the male rat. Toxicol. Ind. Health 15, 48–64.
Gray, L. E., Jr., Wolf, C., Lambright, C., Mann, P., Price, M., Cooper, R. L., and Ostby, J. (1999b). Administration of potentially antiandrogenic pesticides (procymidone, linuron, iprodione, chlozolinate, p,p'-DDE, and ketoconazole) and toxic substances (dibutyl- and diethylhexyl phthalate, PCB 169, and ethane dimethane sulphonate) during sexual differentiation produces diverse profiles of reproductive malformations in the male rat. Toxicol. Ind. Health 15, 94–118.
Hanley, J. A., and McNeil, B. J. (1982). The meaning and use of the area under a receiver operating characteristic (ROC) curve. Radiology 143,29–36.
Hellwig, J., van Ravenzwaay, B., Mayer, M., and Gembardt, C. (2000). Pre- and postnatal oral toxicity of vinclozolin in Wistar and Long-Evans rats. Regul. Toxicol. Pharmacol. 32, 42–50.[CrossRef][Web of Science][Medline]
Imperato-McGinley, J., Binienda, Z., Arthur, A., Mininberg, D. T., Vaughan, E. D., Jr., and Quimby, F. W. (1985). The development of a male pseudohermaphroditic rat using an inhibitor of the enzyme 5-reductase. Endocrinology 116, 807–812.
Imperato-McGinley, J., Binienda, Z., Gedney, J., and Vaughan, E. D., Jr. (1986). Nipple differentiation in fetal male rats treated with an inhibitor of the enzyme 5-reductase: definition of a selective role for dihydrotestosterone. Endocrinology 118, 132–137.
Imperato-McGinley, J., Sanchez, R. S., Spencer, J. R., Yee, B., and Vaughan, E. D. (1992). Comparison of the effects of the 5-reductase inhibitor finasteride and the antiandrogen flutamide on prostate and genital differentiation: Dose-response studies. Endocrinology 131, 1149–1156.
Jegou, B., Peake, R. A., Irby, D. C., and de Kretser, D. M. (1984). Effects of the induction of experimental cryptorchidism and subsequent orchidopexy on testicular function in immature rats. Biol. Reprod. 30, 179–187.[Abstract]
Kratochwil, K. (1977). Development and loss of androgen responsiveness in the embryonic rudiment of the mouse mammary gland. Dev. Biol. 61, 358–365.[CrossRef][Web of Science][Medline]
Latendresse, J. R., Warbrittion, A. R., Jonassen, H, and Creasy, D. M. (2002). Fixation of testes and eyes using a modified Davidson’s fluid: Comparison with Bouin’s fluid and conventional Davidson’s fluid. Toxicol. Pathol. 30,524–533.[Web of Science][Medline]
McIntyre, B. S., Barlow, N. J., and Foster, P. M. D. (2001). Androgen-mediated development in male rat offspring exposed to flutamide in utero: Permanence and correlation of early postnatal changes in anogenital distance and nipple retention with malformations in androgen-dependent tissues. Toxicol. Sci. 62, 236–249.
McIntyre, B. S., Barlow, N. J., and Foster, P. M. D. (2002). Male rats exposed to linuron in utero exhibit permanent changes in anogenital distance, nipple retention, and epididymal malformations that result in subsequent testicular atrophy. Toxicol. Sci 65, 62–70.
McIntyre, B. S., Barlow, N. J., Wallace, D. G., Maness, S. C., Gaido, K. W., and Foster, P. M. D. (2000). Effects of in utero exposure to linuron on androgen-dependent reproductive development in the male Crl:CD(SD)BR rat. Toxicol. Appl. Pharmacol. 167, 87–99.[CrossRef][Web of Science][Medline]
Medical Economics Company (2002). Physician’s Desk Reference, 56th ed., pp. 2172–2178. Medical Economics Company, Inc., Montvale, New Jersey.
Mylchreest, E., Sar, M., Cattley, R. C., and Foster, P. M. D. (1999). Disruption of androgen-regulated male reproductive development by di(n-butyl) phthalate during late gestation in rats is different from flutamide. Toxicol. Appl. Pharmacol. 156, 81–95.[CrossRef][Web of Science][Medline]
Mylchreest, E., Wallace, D. G., Cattley, R. C., and Foster, P. M. D. (2000). Dose-dependent alterations in androgen-regulated male reproductive development in rats exposed to di(n-butyl) phthalate during late gestation. Toxicol. Sci. 55, 143–151.
National Research Council (1996). Guide for the Care and Use of Laboratory Animals. National Academy Press, Washington, DC.
Ostby, J., Kelce, W. R., Lambright, C., Wolf, C. J., Mann, P., and Gray, L. E., Jr. (1999). The fungicide procymidone alters sexual differentiation in the male rat by acting as an androgen-receptor antagonist in vivo and in vitro. Toxicol. Ind. Health 15, 80–93.
Spencer, J. R., Torrado, T., Sanchez, R. S., Vaughan, E. D., Jr., and Imperato-McGinley, J. (1991). Effects of flutamide and finasteride on rat testicular descent. Endocrinology 129, 741–748.
Turner, K. J., Barlow, N. J., Struve, M. F., Wallace, D. G., Gaido, K. W., Dorman, D. C., and Foster, P. M. D. (2002). Effects of in utero exposure to the organophosphate insecticide fenitrothion on androgen-dependent reproductive development in the Crl:CD(SD)BR rat. Toxicol. Sci. 68, 174–183
Veyssiere, G., Berger, M., Jean-Faucher, C., de Turckheim, M., and Jean, C. (1982). Testosterone and dihydrotestosterone in sexual ducts and genital tubercle of rabbit fetuses during sexual organogenesis: Effects of fetal decapitation. J. Steroid Biochem. 17, 149–154.[CrossRef][Web of Science][Medline]
Wilson, J. D., and Lasnitzki, I. (1971). Dihydrotestosterone formation in fetal tissues of the rabbit and rat. Endocrinology 89, 659–668.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  B. G. Rosenberg, H. Chen, J. Folmer, J. Liu, V. Papadopoulos, and B. R. Zirkin Gestational Exposure to Atrazine: Effects on the Postnatal Development of Male Offspring J Androl, May 1, 2008; 29(3): 304 - 311. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. J. Kuhl, S. M. Ross, and K. W. Gaido CCAAT/Enhancer Binding Protein {beta}, But Not Steroidogenic Factor-1, Modulates the Phthalate-Induced Dysregulation of Rat Fetal Testicular Steroidogenesis Endocrinology, December 1, 2007; 148(12): 5851 - 5864. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. P. Longnecker, B. C. Gladen, L. A. Cupul-Uicab, S. P. Romano-Riquer, J.-P. Weber, R. E. Chapin, and M. Hernandez-Avila In Utero Exposure to the Antiandrogen 1,1-Dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) in Relation to Anogenital Distance in Male Newborns from Chiapas, Mexico Am. J. Epidemiol., May 1, 2007; 165(9): 1015 - 1022. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. K. Hotchkiss, C. S. Lambright, J. S. Ostby, L. Parks-Saldutti, J. G. Vandenbergh, and L. E. Gray Jr Prenatal Testosterone Exposure Permanently Masculinizes Anogenital Distance, Nipple Development, and Reproductive Tract Morphology in Female Sprague-Dawley Rats Toxicol. Sci., April 1, 2007; 96(2): 335 - 345. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Yu, M. Wu, S. Lin, and P. Talbot Cigarette Smoke Toxicants Alter Growth and Survival of Cultured Mammalian Cells Toxicol. Sci., September 1, 2006; 93(1): 82 - 95. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
O. Genbacev-Krtolica Highlight for Phenols, Quinolines, Indoles, Benzene and 2-Cyclopenten-1-ones Are Oviduct Toxicants in Cigarette Smoke, by Prue Talbot, Karen Riveles, and Ryan Rosa: List of Tobacco-Smoke Constituents That Are Harmful for Reproduction Grows--Passive Smokers May Be at Risk Toxicol. Sci., July 1, 2005; 86(1): 4 - 5. [Full Text] [PDF]
|
|
|
|
 |
|
 K. Liu, K. P. Lehmann, M. Sar, S. S. Young, and K. W. Gaido Gene Expression Profiling Following In Utero Exposure to Phthalate Esters Reveals New Gene Targets in the Etiology of Testicular Dysgenesis Biol Reprod, July 1, 2005; 73(1): 180 - 192. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 F. M. Poulet, R. Veneziale, P. M. Vancutsem, P. Losco, K. Treinen, and R. E. Morrissey Ziracin-Induced Congenital Urogenital Malformations in Female Rats Toxicol Pathol, April 1, 2005; 33(3): 320 - 328. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||