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Aromatase Activity in Sheepshead Minnow (Cyprinodon variegatus), Exposed to 17B-Trenbolone or 17B-estradiol in a Tier II Two-Generation Test
Citation:
GUTJAHR-GOBELL, R. E., G. M. CRIPE, G. E. ZAROOGIAN, S. C. LAWS, AND L. J. MILLS. Aromatase Activity in Sheepshead Minnow (Cyprinodon variegatus), Exposed to 17B-Trenbolone or 17B-estradiol in a Tier II Two-Generation Test. Presented at SETAC North American 29th Annual Meeting, Tampa, FL, November 16 - 20, 2008.
Impact/Purpose:
There are two distinct isozymes of aromatase that have been characterized in fish, one predominating in brains and another in ovaries. We tested the hypothesis that endocrine-disrupting chemicals, that alter fish reproduction will also modulate activity of the steroidogenic enzyme aromatase. The pharmaceutical 17ß-trenbolone (ß-TBOH), an androgen, and 17ß-estradiol (E2), an estrogen, affect fish reproduction in laboratory exposures. Sheepshead minnow (Cyprinodon variegatus) were exposed in the laboratory in two multi-generational experiments, (17ß-trenbolone or 17ß-estradiol) using early life-stage and chronic exposure guidelines.
Description:
We tested the hypothesis that endocrine disrupting chemicals (EDCs) that alter fish reproduction will also modulate activity of the steroidogenic enzyme aromatase. There are two distinct isozymes of aromatase that have been characterized in fish, one predominating in brains and another in ovaries. The pharmaceutical, 17ß trenbolone (ß TBOH), an androgen, and 17ß estradiol (E2), an estrogen, affect fish reproduction in laboratory exposures. Sheepshead minnow (Cyprinodon variegatus) were exposed in the laboratory in two experiments to ß TBOH (0.01, 0.04, 0.2, 1.0 and 5.0 μg/L) or E2 (0.012, 0.03, 0.08, 0.2 and 0.5 μg/L) using early life stage and chronic exposure guidelines. Multi generational experiments began with three week exposures of actively spawning adults (F0) and continued through the first (F1) generation. Brains (♂ and ♀) and ovaries of both F0 and the F1 generations were dissected and flash frozen. Brain (♂ and ♀) and ovary microsomes were isolated and assayed for aromatase activity using the tritiated water method. In the ß TBOH exposed F0 generation, results indicate a significantly lower aromatase activity in F0 ♂ brains for all doses, while there were no significant differences in aromatase activity in F0 ♀ brains at any dose. In theß TBOH exposed F1 generation, there was a significantly lower aromatase activity in ♂ and ♀ brains. Ovarian aromatase activity was significantly higher in the F0 generation exposed to ß TBOH, but, not in the F1 generation. On the other hand, sheepshead minnow ovaries exposed to E2 had a significantly lower aromatase activity in both the F0 and F1 generations. In summary, our results show that exposure of sheepshead minnow to ß TBOH: 1) alters ♂ brain aromatase activity in both the F0 and F1 generations; 2) alters ♀ brain aromatase activity in the F1 generation, but not F0 generation; and 3) alters ovary aromatase activity in the F0 generation, but not the F1 generation. Exposure to E2 alters ovary aromatase activity in both the F0 and F1 generations. Our results suggest that EDCs that alter fish reproduction may differentially affect the aromatase activity of the two distinct isozymes of aromatase in sheepshead minnow.