hCG-stimulated ovarian carbonyl reductase in relation to preovulatory ovarian follicular growth.

The relationship between carbonyl reductase, which is localized in the theca and interstitial cells, and ovarian follicular development was evaluated by measuring the enzyme activity and concentration of carbonyl reductase, and examining its immunohistochemical localization in immature rats treated with equine chorionic gonadotrophin (eCG), ovine(o) FSH and hCG. eCG and oFSH were administered s.c. to 26-day-old rats, and the ovaries were isolated 48 and 72 h after treatment. hCG was administered s.c. 48 h (at 28 days of age) after eCG or oFSH, and the ovaries were isolated 6 or 9 h after treatment. Both eCG and oFSH significantly increased the ovarian carbonyl reductase concentration 48 h after treatment compared with the saline-treated group, but the increase with eCG was approximately twice that with oFSH. Seventy-two hours after treatment, eCG further increased both carbonyl reductase activity and its concentration. Ovulation was also induced. oFSH stimulated only ovarian follicular growth without further increase in either activity or concentration. In addition, eCG increased the immunoreactivity to anti-carbonyl reductase antibody in the theca and interstitial cells, but oFSH did not. Treatment with hCG in saline-pretreated rats increased carbonyl reductase activity by 2.8-fold and carbonyl reductase concentration by 4.1-fold after 9 h compared with the 0 h concentration, without producing the large follicles observed with eCG and oFSH. However, the stimulatory effect of hCG on ovarian carbonyl reductase in eCG- or oFSH-pretreated rats was weaker than that in saline-pretreated rats. These results suggest that ovarian carbonyl reductase is induced by LH/hCG but not by FSH and that the enzyme induced by hCG is unrelated to preovulatory ovarian follicular growth.