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EFFECTS OF METHYLTESTOSTERONE ON AROMATASE ACTIVITY IN ADULT FATHEAD MINNOW
Citation:
Hornung, M. W., E J. Durhan, K M. Jensen, J J. Korte, M D. Kahl, AND G T. Ankley. EFFECTS OF METHYLTESTOSTERONE ON AROMATASE ACTIVITY IN ADULT FATHEAD MINNOW. Presented at Joint Regional SETAC/SOT Annual Meetings, USEPA, Duluth, MN, April 9-10, 2002.
Description:
The effect of methyltestosterone (MT) in a fathead minnow 21-d reproduction assay was previously determined in this laboratory. It was found that methyltestosterone at 0.2 and 2 mg/L produced both estreogenic and androgenic effects. Both concentrations of methyltestosterone produced significant increases in serum vitellogenin in both the males and females. Methyltestosterone also induced the formation of tubercles on the heads of the females; a structure normally only encountered on breeding males. The current study is an attempt to begin to explain some of these effects and included a MT concentration an order of magnitude below that of the original study. We found that the tubercles were again produced in the female fathead minnows at 0.2 mg MT/L and at 0.02 mg/L, demonstrating that this effect is a sensitive marker of androgen exposure. It was hypothesized that the large increase in vitellogenin in the males and was due to the conversion of methyltestosterone to methylestradiol via aromatase enzyme activity. In pooled ovarian tissue microsomes from fathead minnows at 7 days post exposure, the aromatase enzyme activity was significantly decreased in the methyltestosterone treated fish compared to treated animals. There was no difference in brain aromatase between sexes within a treatment group. Aromatase activity was reduced to 53% and 44% of control activity, respectively, in the 0.02 and 0.2 mg MT/L treatment groups. This contradicts the hypothesis that brain aromatase activity was increased to produce methylestradiol. However, the conversion to methylestradiol may have occurred earlier following exposure and decreased subsequently. Tissue analysis efforts are currently underway to determine whether methylestradiol is present in the sampled fathead minnows from this study. This abstract does not necessarily reflect USEPA policy.