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THE EFFECTS OF METHOXYCHLOR AND METHYLTESTOSTERONE ON REPRODUCTION IN A SHORT-TERM ASSAY USING THE FATHEAD MINNOW (PIMEPHALES PROMELAS)
Citation:
Ankley, G T., M D. Kahl, K M. Jensen, J J. Korte, E A. Makynen, AND J E. Tietge. THE EFFECTS OF METHOXYCHLOR AND METHYLTESTOSTERONE ON REPRODUCTION IN A SHORT-TERM ASSAY USING THE FATHEAD MINNOW (PIMEPHALES PROMELAS). Presented at Society of Toxicology National Meeting, San Francisco, CA, March 25-29, 2001.
Description:
The effect of chemicals on reproduction of fishes is an area of great uncertainty. Because full life cycle testing of fish is cost prohibitive, we have developed a short-term assay to assess the effects of chemicals on reproduction of adult fathead minnows (Pimephales promelas). The test is initiated with reproductively mature animals and is comprised of a pre-exposure phase followed by chemical exposure of up to 21 days. Several endpoints are monitored in this assay as indicators of reproductive status, including: fecundity, fertility, plasma vitellogenin (Vg) concentrations, plasma sex steroid concentrations, gross morphology, and histology of the gonads. We have evaluated this assay using two reproductive toxicants, methoxychlor (an esoteric xenobiotic chemical) and methyltestosterone (a model androgen). Both chemicals reduced reproductive output at aqueous exposure concentrations for methyltestosterone. Methoxychlor decreased plasma concentrations of B-estradiol (E2) in females and testosterone (T) in males. Methoxychlor exposure had no effect on E2 concentrations in males, but did induce plasma Vg in males. This response is consistent with activation of the estrogen receptor by the parent compound or its metabolites. Methyltestosterone decreased plasma concentrations of E2 and T in females and of T in males and resulted in adverse effects on the gonads of both sexes. Direct androgenic effects of methyltestosterone were observes in females, as they were induced to exhibit male secondary sexual characteristics. Methyltestosterone also markedly increased plasma concentrations of Vg in males and females suggesting that aromatization of the androgen to a form capable of binding the estrogen receptor may have occurred. These studies demonstrate the potential utility of this multi-endpoint assay for identifying reproductive toxins that affect estrogen and androgen pathways of fish.