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A SHORT TERM REPRODUCTION TEST WITH THE FATHEAD MINNOW (PIMEPHALES PROMELAS): LL. METHOD EVALUATION
Citation:
Jensen, K M., M D. Kahl, G W. Holcombe, J J. Korte, E A. Makynen, AND G T. Ankley. A SHORT TERM REPRODUCTION TEST WITH THE FATHEAD MINNOW (PIMEPHALES PROMELAS): LL. METHOD EVALUATION. Presented at SETAC 8th Annual Meeting, Bloomington, MN, April 13-14, 2000.
Description:
The U.S. Environmental Protection Agency is required to develop, validate, and implement a screening program for identifying potential endocrine-disrupting chemicals. The objective of this research was to evaluate the recommended short term test which assesses alterations in reproduction and endocrine function in the fathead minnow (Pimephales promelas) as a basis for identifying endocrine-disrupting chemicals. Methoxychlor and methyltestosterone were selected as test chemicals representative, respectively, of estrogenic and androgenic mechanisms of action. Both chemicals caused a significant decrease in fecundity of the fish at concentrations of 0.55 ug/L (methoxychlor) and 0.2 mg/L (methyltestosterone). Methoxychlor also caused a significant induction of plasma vitellogenin in males, a response consistent with activation of the estrogen receptor by the pesticide (or its metabolites). In addition to decreased fecundity, methyltestosterone decreased plasma concentrations of sex steroids (testosterone, ll-ketotestosterone, B-estradiol) and adversely affected gonadal status (as evaluated by relative weight and histopathology) of both sexes. The androgenic nature of methyltestosterone was clearly expressed as masculinization of exposed females via formation of nuptial tubercles, structures normally present only in sexually-active males. The androgen also caused a significant induction of plasma vitellogenin in both males and females; this unexpected "estrogenic" response was most likely due to aromatization of the androgen to a form capable of binding to the estrogen receptor. These studies demonstrate the utility of the fathead minnow assay for adentifying chemicals that exert reproductive toxicity through alterations in endocrine systems controlled by estrogens and androgens.