In vitro effect of a fish gonadotropin on aromatase and 17 beta-hydroxysteroid dehydrogenase activities in the ovary of the rainbow trout (Salmo gairdneri Rich.).

Aromatase activity has been studied in the rainbow trout ovary in a perifusion system. During early vitellogenesis, as in other stages of the annual cycle, the ovaries were capable of aromatizing androstenedione and testosterone. Aromatase activity increased from the postovulatory stages to exogenous vitellogenesis. When highly purified salmon glycoprotein maturational gonadotropin was added to the medium (50 ng/ml), the androstenedione/testosterone ratio was reduced by half. This indicates a stimulation of 17 beta-hydroxysteroid dehydrogenase activity favourizing the formation of testosterone. At a concentration of 50, 150 or 300 ng/ml, the gonadotropin inhibited between 13 and 38 p. 100 of the aromatase enzymatic activity.