Cyclic change in 3 alpha-hydroxysteroid dehydrogenase in rat ovary during the estrous cycle

3 alpha-Hydroxysteroid dehydrogenase (3 alpha-HSD) activity and content in the rat ovary were measured at various stages of the estrous cycle, and the enzyme protein in the ovary was localized by immunohistochemistry. The cyclic change of ovarian 3 alpha-HSD activity towards 5 alpha-dihydrotestosterone (5 alpha-DHT) as a substrate was characterized by two peaks. The first peak occurred at 0800 h on proestrus; then the reductase activity decreased and reached its minimum at 2000 h on proestrus. Thereafter, it gradually increased, reaching the second peak (170% of the value at 2000 h on proestrus) at noon of estrus. Quantitative analysis by immunoblotting revealed that the alteration in 3 alpha-HSD content in the rat ovary during the estrous cycle was essentially similar to that in 5 alpha-DHT reductase activity. Changes in the reductase activities towards 5 alpha-androstane-3,17-dione and 5 alpha-DHT and in the dehydrogenase activity towards androsterone in the ovary were entirely different from those in the 5 alpha-DHT reductase activity and 3 alpha-HSD content; on the other hand, the change in carbonyl reductase activity towards p-nitroacetophenone was similar to changes in 5 alpha-DHT reductase activity and 3 alpha-HSD content. Therefore, p-nitroacetophenone may be a useful substrate, instead of 5 alpha-DHT, for detection of 3 alpha-HSD activity at a high sensitivity, since the p-nitroacetophenone reductase activity was 10-fold higher than the 5 alpha-DHT reductase activity. The enzyme was primarily localized in the granulosa cells and CL cells. At 2000 h on proestrus, however, the overall intensity of immunostaining in the granulosa cells of the Graafian follicles was markedly diminished. In addition, immunoreactivity in the CL cells at 0800 h on estrus was observed only in the cells outlining the CL in some cases.