VAJDA, A.M.; NORRIS, D.O.: Interactions of Gonadal steroids and Dioxin on Gonaduct growth in larval Tiger Salamanders, Ambystoma tigrinum

Modulation of steroid action in response to diverse environmental cues yields potentially adaptive phenotypic diversity in reproductive characters. Exposure to environmental signals of anthropogenic origin (i.e. chemical pollutants) might interfere with steroid hormone action, yielding diverse state-dependent outcomes that may represent maladaptations of life-history phenotype. Dioxins, through interaction with the aryl hydrocarbon receptor, can interfere with steroid function by altering hormone synthesis, enhancing ligand metabolism, down-regulating receptor levels, and intitiating cross-talk with steroid signal transduction pathways. The present study investigated the effects of the dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on steroid-dependent development of amphibian gonaducts. Larval male and female tiger salamanders (Ambystoma tigrinum ), with immature gonads, were immersed in a sublethal solution of technical-grade TCDD (3.3 ppb) and injected with the androgen dihydrotestosterone (DHT). Morphometrics were used to analyze the effects and interactions of androgen and TCDD treatment on larval wolffian ducts. In A. tigrinum, growth of these tissues is androgen dependent and is antagonized by estradiol. DHT increased wolffian duct epithelial area. TCDD antagonized the androgenic actions of DHT on wolffian duct epithelial area. In the absence of exogenous androgen, TCDD mimicked estradiol by reducing wolffian duct epithelial area. 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 chemicals.