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ToxSci Advance Access originally published online on June 14, 2008
Toxicological Sciences 2008 105(1):51-58; doi:10.1093/toxsci/kfn119
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Published by Oxford University Press 2008.

Exposure of Xenopus laevis Tadpoles to Cadmium Reveals Concentration-dependent Bimodal Effects on Growth and Monotonic Effects on Development and Thyroid Gland Activity

Bibek Sharma* and Reynaldo Patiño{dagger},1

* Department of Natural Resources Management, Texas Tech University, Lubbock, Texas 79409-2120 {dagger} USGS Texas Cooperative Fish and Wildlife Research Unit, Texas Tech University, Lubbock, Texas 79409-2120

1 To whom correspondence should be addressed at USGS Texas Cooperative Fish & Wildlife Research Unit, Texas Tech University, Lubbock, TX 79409-2120, USA. Fax: (806) 742-2946. E-mail: reynaldo.patino{at}ttu.edu.

Received March 7, 2008; accepted June 10, 2008


  Abstract

Xenopus laevis were exposed to 0–855 µg cadmium (Cd)/l (measured concentrations) in FETAX medium from fertilization to 47 days postfertilization. Measurements included embryonic survival and, at 47 days, tadpole survival, snout-vent length, tail length, total length, hindlimb length, weight, Nieuwkoop-Faber (NF) stage of development, initiation of metamorphic climax (≥ NF 58), and thyroid follicle cell height. Embryonic and larval survival were unaffected by Cd. Relative to control tadpoles, reduced tail and total length were observed at 0.1- 8 and at 855 µg Cd/l; and reduced snout-vent length, hindlimb length, and weight were observed at 0.1–1 and at 855 µg Cd/l. Mean stage of development and rate of initiation of climax were unaffected by Cd at 0–84 µg/l; however, none of the tadpoles exposed to 855 µg Cd/l progressed beyond mid-premetamorphosis (NF 51). Thyroid glands with fully formed follicles were observed in all tadpoles ≥ NF 49 examined. Follicle cell height was unaffected by Cd at 0–84 µg/l but it was reduced at 855 µg/l; in the latter, cell height was reduced even when compared with NF 49–51 tadpoles pooled from the 0 to 84 µg Cd/l groups. In conclusion, (1) Cd affected tadpole growth in a bimodal pattern with the first and second inhibitory modes at concentrations below and above 84 µg Cd/l, respectively; (2) exposure to high Cd concentrations (855 µg/l) reduced thyroid activity and arrested tadpole development at mid-premetamorphosis; and (3) unlike its effect on growth, Cd inhibited tadpole development and thyroid function in a seemingly monotonic pattern.

Key Words: cadmium; growth; metamorphosis; thyroid; amphibian.


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