EFFECTS OF THE ANDROGENIC GROWTH PROMOTER 17-Β-Trenbolone ON FECUNDITY AND REPRODUCTIVE ENDOCRINOLOGY OF THE FATHEAD MINNOW

Abstract

Trenbolone acetate is a synthetic steroid that is extensively used in the United States as a growth promoter in beef cattle. The acetate is administered to livestock via slow-release implants; some is converted by the animal to 17-beta-trenbolone, a relatively potent androgen receptor agonist in mammalian systems. Recent studies indicate that excreted 17-beta-trenbolone is comparatively stable in animal waste, suggesting the potential for exposure to aquatic animals via direct discharge, runoff, or both. However, little is known concerning the toxicity of trenbolone to fish. Our goal was to assess the effects of 17-beta-trenbolone on reproductive endocrinology of the fathead minnow (Pimephales promelas). An in vitro competitive binding study with the fathead minnow androgen receptor demonstrated that 17-beta-trenbolone had a higher affinity for the receptor than that of the endogenous ligand, testosterone. Male and female fish were exposed for 21 d to nominal (target) concentrations of 17-beta-trenbolone ranging from 0.005 to 50 microg/L. Fecundity of the fish was significantly reduced by exposure to measured test concentrations > or = 0.027 microg/ L. The 17-beta-trenbolone was clearly androgenic in vivo at these concentrations, as evidenced by the de novo production in females of dorsal (nuptial) tubercles, structures normally present only on the heads of mature males. Plasma steroid (testosterone and beta-estradiol) and vitellogenin concentrations in the females all were significantly reduced by exposure to 17-beta-trenbolone. The 17-beta-trenbolone also altered reproductive physiology of male fathead minnows, albeit at concentrations much higher than those producing effects in females. Males exposed to 17-beta-trenbolone at 41 microg/L (measured) exhibited decreased plasma concentrations of 11-ketotestosterone and increased concentrations of beta-estradiol and vitellogenin. Overall, our studies indicate that 17-beta-trenbolone is a potent androgen and reproductive toxicant in fish. Given the widespread use of trenbolone acetate as a growth promoter, and relative stability of its metabolites in animal wastes, further studies are warranted to assess potential ecological risk.

Use of chemical mixtures to differentiate mechanisms of endocrine action in a small fish model

“…The basis of the approach lies in evaluating whether test chemicals block occurrence of an in vivo response mediated through the AR. Studies in our lab and elsewhere have shown that the synthetic androgen 17␤-trenbolone (TB) binds with high affinity to fish AR(s) and masculinizes female fish at concentrations in water in the range of 20-50 ng/L (Ankley et al, 2003;Wilson et al, 2004;Seki et al, 2006). In the fathead minnow, masculinization is manifested by a proliferation and thickening of the dorsal pad and the de novo development of craniofacial nuptial tubercles, external structures which can be visually detected and easily quantified ).…”

Coupled reversion and stream-hyporheic exchange processes increase environmental persistence of trenbolone metabolites

“…Field observations have documented 1,700 ng l À 1 17a-TBOH in manure lagoons 9 , and 55 ± 22 ng g À 1 in solid manure and surface soils 10 . TBA metabolite exposure is problematic for ecosystem health because 17a-TBOH and 17b-TBOH are potent endocrine disruptors, with exposure to as little as 10-30 ng l À 1 significantly reducing fecundity, resulting in phenotypic sex reversal in fish, or altering endocrine function [11][12][13] .…”

Development of methods to detect occurrence and effects of endocrine‐disrupting chemicals: Fueling a fundamental shift in regulatory ecotoxicology

“…Further work extended this basic design to EDC-oriented tests with other small fish species, including the medaka (Oryzias latipes) and zebrafish (Danio rerio) [4]. As part of the validation of the 21-d assay, several model chemicals were tested, including estrogen receptor agonists such as 17b-estradiol and methoxychlor [2,3] and androgen receptor agonists such as methyltestosterone and 17b-trenbolone [3,5]. Tyler et al [6] described a test method specific for estrogens that focused on the induction of vitellogenin in fathead minnow early life stages, an approach that aligned well with the commonly utilized 30-d survival and growth assay in this species and also was recommended as a reasonable design for detecting estrogenic EDCs [1].…”