CYCLIC CHANGE IN 3-ALPHA-HYDROXYSTEROID DEHYDROGENASE IN RAT OVARY DURING THE ESTROUS-CYCLE

3 alpha-Hydroxysteroid dehydrogenase (3 alpha-HSD) activity and conten t in the rat ovary were measured at various stages of the estrous cycl e, and the enzyme protein in the ovary was localized by immunohistoche mistry. The cyclic change of ovarian 3 alpha-HSD activity towards 5 al pha-dihydrotestosterone (5 alpha-DHT) as a substrate was characterized by two peaks, The first peak occurred al 0800 h on proestrus; then th e reductase activity decreased and reached its minimum at 2000 h on pr oestrus. Thereafter, it gradually increased, reaching the second peak (170% of the Value at 2000 h on proestrus) at noon of estrus. Quantita tive analysis by immunoblotting revealed that the alteration in 3 alph a-HSD content in the rat ovary during the estrous cycle was essentiall y similar to that in 5 alpha-DHT reductase activity, Changes in the re ductase activities towards 5 alpha-androstane-3, 17-dione and 5 alpha- DHT and in the dehydrogenase activity towards androsterone in the ovar y were entirely different from those in the 5 alpha-DHT reductase acti vity and 3 alpha-HSD content; on the other hand, the change in carbony l reductase activity towards p-nitroacetophenone was similar to change s in 5 alpha-DHT reductase activity and 3 alpha-HSD content. Therefore , p-nitroacetophenone may be a useful substrate, instead of 5 alpha-DH T, 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, th e overall intensity of immunostaining in the granulosa cells of the Gr aafian follicles was markedly diminished, in addition, immunoreactivit y in the CL cells at 0800 h on estrus was observed only in the cells o utlining the CL in some cases.