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

Abstract

3α-Hydroxysteroid dehydrogenase (3α-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 3α-HSD activity towards 5α-dihydrotestosterone (5α-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 3α- HSD content in the rat ovary during the estrous cycle was essentially similar to that in 5α-DHT reductase activity. Changes in the reductase activities towards 5α-androstane-3,17-dione and 5α-DHT and in the dehydrogenase activity towards androsterone in the ovary were entirely different from those in the 5α-DHT reductase activity and 3α-HSD content; on the other hand, the change in carbonyl reductase activity towards p-nitroacetophenone was similar to changes in 5α-DHT reductase activity and 3α-HSD content. Therefore, ρ- nitroacetophenone may be a useful substrate, instead of 5α-DHT, for detection of 3α-HSD activity at a high sensitivity, since the ρ- nitroacetophenone reductase activity was 10-fold higher than the 5α-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.