Reproductive toxicity of vinclozolin in the fathead minnow: Confirming an anti‐androgenic mode of action

The objective of the present study was to characterize responses of the reproductive endocrine system of the fathead minnow (Pimephales promelas) to the fungicide vinclozolin (VZ), using a 21-d reproduction assay, and a shorter-term (approximately two weeks) test in which fish were cotreated with the VZ (a putative anti-androgen) and the androgen 17beta-trenbolone (TB). Effects on fecundity, gonadal histology, secondary sexual characteristics, reproductive hormones, and relative abundance of androgen receptor (AR) and 11beta-hydroxysteroid dehydrogenase (11betaHSD) mRNA transcripts were evaluated in one or both of these studies. Fecundity of VZ-exposed fish was decreased in a concentration-dependent manner in the 21-d test, culminating in complete reproductive failure at a concentration of 700 microg/L. Exposure to VZ decreased expression of male secondary sexual characteristics -- an effect typical of anti-androgens. The finding that exposure of females to TB-induced expression of prominent, male-like tubercles, which could be effectively blocked with VZ, provides powerful evidence of the anti-androgenic activity of VZ in vivo. In the two experiments VZ produced several responses possibly indicative of compensation or adaptation of the fish to the anti-androgen, including increases in gonad weight, AR and 11 betaHSD mRNA transcript abundance, and ex vivo gonadal production of testosterone and 11-ketotestosterone. Overall, our results demonstrate that the model anti-androgen VZ, which also is an environmental contaminant, impairs reproductive success of fathead minnows and elicits endocrine responses consistent with an anti-androgenic mode of action.