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EFFECTS OF METHYLTOSTERONE ON AROMATASE ACTIVITY IN ADULT FATHEAD MINNOW
Citation:
Hornung, M. W., B C. Butterworth, K M. Jensen, J J. Korte, M D. Kahl, E A. Makynen, AND G T. Ankley. EFFECTS OF METHYLTOSTERONE ON AROMATASE ACTIVITY IN ADULT FATHEAD MINNOW. Presented at 22nd Annual SETAC Meeting, Baltimore, MD, November 11-15, 2001.
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 estrogenic and androgenic effects. Both concentrations of methyltestosterone produced significant increases in serum vitellogenin in both males and females. Methyltestosterone also induced the formation of tubercles on the heads of females, a structure normally 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 females 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 control. Brain aromatase activity is S9 fractions from individual fish was also decreased in the 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 mat 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.