Effects of steroids and dioxin (2,3,7,8-TCDD) on the developing wolffian ducts of the tiger salamander Ambystoma tigrinum.
The present study investigated the effects of the dioxin,
2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on steroid-dependent
development of amphibian gonaducts. Sexually undifferentiated larval
tiger salamanders (Ambystoma tigrinum), with immature gonads were
immersed in a sub lethal solution of technical-grade TCDD and injected
with dihydrotestosterone (DHT) or estradiol ([E.sub.2]). Morphometrics were used to analyze the effects and interactions of the sex-steroids
and TCDD treatments on wolffian ducts. In sexually differentiated A.
tigrinum larvae, growth of this tissue is androgen-dependent and is
antagonized by estradiol. We found that in sexually undifferentiated A.
tigrinum, mean wolffian duct epithelial area was increased by both
steroid treatments. DHT stimulated an increase in the size and number of
cells while [E.sub.2] only stimulated an increase in cell size. In the
absence of exogenous steroid, TCDD mimicked [E.sub.2] by increasing mean
cell size in the wolffian duct. TCDD agonized the stimulatory action of
DHT on wolffian duct cell size. TCDD had no effect on wolffian duct
epithelium in [E.sub.2]-treated animals. These findings implicate
environmental dioxins as potentially important modulators of amphibian
reproduction and further validate the utility of urodele gonaducts as a
useful bioassay for the detection of endocrine-active environmental
Alan M. Vajda * and David O. Norris *. Department of EPO Biology,
University of Colorado, Boulder.
* Denotes membership in the Colorado-Wyoming Academy of Science.