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A SHORT-TERM REPRODUCTION TEST WITH THE FATHEAD MINNOW PIMEPHALES PROMELAS: II. METHOD EVALUATION
Citation:
Ankley, G T., M D. Kahl, J J. Korte, K M. Jensen, AND E A. Makynen. A SHORT-TERM REPRODUCTION TEST WITH THE FATHEAD MINNOW PIMEPHALES PROMELAS: II. METHOD EVALUATION. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. SETAC Press, Pensacola, FL, 20:1276-1290, (2001).
Description:
The objective of these studies was to evaluate a short-term test that 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 of estrogenic and androgenic mechanisms of action, respectively. Both chemicals caused a significant decrease in fecundity of the fish at nominal concentrations of 5.0 ug/L (methoxychlor) and 0.2 mg/L (methyltestosterone). Methoxychlor decreased plasma concentrations of one or more steroids (testosterone, 11-ketotestosterone, B-estradiol) in both sexes, and caused a significant induction of plasma vitellogenin in males, a response consistent with activation of the estrogen receptor by the pesticide (or its metabolites). Methyltestosterone decreased plasma concentrations of sex steroids, and adversely affected gonadal status (as evaluated by relative weight and histopathology) in both sexes, in addition to decreasing fecundity. The androgenic nature of methyltestosterone was clearly expressed as masculinization of exposed females via formation of nuptial tubercles, structures normally present only in reproductively-active males. The chemical 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 identifying chemicals that exert reproductive toxicity through alterations in endocrine systems controlled by estrogens and androgens.