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ToxSci Advance Access published online on January 19, 2005
Toxicological Sciences, doi:10.1093/toxsci/kfi087
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Toxicological Sciences © Society of Toxicology 2005; all rights reserved.
Received December 6, 2004
Accepted January 10, 2005

Reproductive and Developmental Toxicology

Sub-Chronic Exposure to Low Concentrations of Di-n-Butyl Phthalate Disrupts Spermatogenesis in Xenopus laevis Frogs

Shannon K. Lee 1 and D. N. Rao Veeramachaneni 1*

1 Animal Reproduction and Biotechnology Laboratory, Colorado State University, Fort Collins, CO 80523

* To whom correspondence should be addressed.
D. N. Rao Veeramachaneni, E-mail: rao{at}colostate.edu


  Abstract

Due to its widespread use and production, di-n-butyl phthalate (DBP) has become an environmental contaminant. It has been detected in variety of environmental strata worldwide, including air, water and soil. Also, monobutyl phthalate, the major metabolite of DBP, has been detected in a variety of human matrices. As a proven endocrine disruptive compound, DBP may contribute to global amphibian declines at much lower concentrations than tested thus far. We evaluated the effects of low concentrations of DBP on spermatogenesis in Xenopus laevis, the African clawed frog.

Xenopus tadpoles were exposed to 0, 0.1, 0.5, 1.0, 5.0, or 10.0 ppm DBP beginning at sexual differentiation (Nieuwkoop and Faber stage 52; 3 wk of age) and continuing until 100% of controls metamorphosed (stage 66; 8 wk of age). Upon necropsy at 33wk, 4-6% of DBP-treated frogs had only one testis and 2-4% had retained oviducts. In all DBP treatment groupsseminiferous tubule diameter and the average number of germ cell nests per tubule were lower and the number of tubules with no germ cells was significantly higher (p < 0.05). The percent of secondary spermatogonial cell nests significantly decreased (p < 0.05) in 1.0, 5.0 and 10.0 ppm groups. Several lesions occurred in DBP-exposed testes including denudation of germ cells, vacuolization of Sertoli cell cytoplasm, thickening of lamina propria of seminiferous tubules, and focal lymphocytic infiltration. Entire sections of testes containing almost exclusively mature spermatozoa were found in 1.0, 5.0 and 10.0 ppm DBP-exposed testes, indicating impairment of spermiation. Testicular hypoplasia and seminiferous tubular dysgenesis were also evident in DBP-treated frogs. Thus, sub-chronic exposure to low concentrations of DBP impairs spermatogenesis in Xenopus laevis frogs.

Keywords: amphibian declines; sexual differentiation; testicular dysgenesis; testicular hypoplasia; impaired spermiation; Sertoli cell lesions.
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