title: Ovarian regulation of hypothalamic and pituitary progestin-metabolizing enzyme activities.
abstract: Progesterone 5 alpha-reductase activity and 5 alpha-dihydroprogesterone 3 alpha-hydroxysteroid oxidoreductase (3 alpha-HSOR) activities (NADH-linked) were measured in hypothalamic and pituitary tissues from rats during various stages of the estrous cycle and in ovariectomized rats treated with 17 beta-estradiol or vehicle. Enzyme assays were performed using 3H-labeled steroid substrates and reverse isotopic dilution analyses. Pituitary 5 alpha-reductase activity fluctuated over the estrous cycle, with peak levels observed on proestrus, estrus, and metestrus and lowest levels on diestrous 1 and 2 of 5-day cycling rats. Pituitary NADH-linked 3 alpha-HSOR activity also fluctuated over the estrous cycle, paralleling 5 alpha-reductase activity. The pituitary NADPH-linked 3 alpha-HSOR activity and three hypothalamic enzyme activities, the 5 alpha-reductase, NADH-linked, and NADPH-linked 3 alpha-HSOR activities, did not change over the estrous cycle. After ovariectomy (10 days), pituitary 5 alpha-reductase activity was elevated 10- to 12-fold relative to mean levels in intact rats, while the pituitary NADH-linked 3 alpha-HSOR activity was elevated 4- to 5-fold. Treatment for 3 days with estradiol benzoate (10 micrograms/day) significantly reduced both pituitary 5 alpha-reductase and NADH-linked 3 alpha-HSOR activities to about half the levels observed in ovariectomized rats. The pituitary NADPH-linked 3 alpha-HSOR activity was unaffected by ovariectomy. After ovariectomy, a small decrease was observed in the hypothalamic 5 alpha-reductase; no differences were observed in the NADH-linked or NADPH-linked 3 alpha-HSOR activities of the hypothalamus compared to mean levels in cyclic rats. The results suggest a role of the ovary in the regulation of the pituitary and hypothalamic progesterone 5 alpha-reductase and pituitary NADH-linked 5 alpha-dihydroprogesterone 3 alpha-HSOR activities.
mesh_terms: D000818:Animals; D002369:Castration; D004971:Estrus; D005260:Female; D007031:Hypothalamus / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010053:Ovary / Q000502:physiology*; D010902:Pituitary Gland / Q000201:enzymology*; D011247:Pregnancy; D011375:Progesterone Reductase / Q000378:metabolism; D011372:Progestins / Q000378:metabolism*; D051381:Rats; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D011372:Progestins; D009243:NAD; D009249:NADP; D011375:Progesterone Reductase