Changes in oestrogen biosynthesis in preovulatory rat follicles after blockage of ovulation with pentobarbitone sodium.
Follicles isolated 1 and 2 days after pentobarbitone sodium injection at pro-oestrus were incubated with C-21 steroids or aromatizable C-19 steroids. Addition of testosterone or androstenedione (50 ng/ml) increased oestradiol production by ovulation-blocked follicles, while addition of progesterone or 17 alpha-hydroxyprogesterone was ineffective. LH-stimulated oestradiol production was lower in follicles isolated 1 and 2 days after pentobarbitone sodium injection, but progesterone production was elevated compared to pro-oestrous follicles. Total steroidogenesis, measured by pregnenolone production in the presence of inhibitors of pregnenolone conversion, did not differ on the 3 days. The activity of C17-20 lyase, measured in follicular homogenates, decreased between pro-oestrus and the next day. Aromatase and 17 alpha-hydroxylase activities also decreased, but the activity of these enzymes was always considerably higher than that of C17-20 lyase. It is concluded that the decrease in follicular oestradiol production after injection of pentobarbitone sodium was due primarily to a decrease in the activity of the enzyme system responsible for the conversion of 17 alpha-hydroxyprogesterone to androstenedione, thereby limiting the amount of substrate available for aromatization to oestrogen.
D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase / Q000378:metabolism; D000446:Aldehyde-Lyases / Q000378:metabolism; D000818:Animals; D001141:Aromatase / Q000378:metabolism; D004958:Estradiol / Q000096:biosynthesis*; D004971:Estrus; D005260:Female; D066298:In Vitro Techniques; D007986:Luteinizing Hormone / Q000494:pharmacology; D006080:Ovarian Follicle / Q000187:drug effects / Q000378:metabolism*; D010060:Ovulation / Q000187:drug effects; D010424:Pentobarbital / Q000494:pharmacology; D011247:Pregnancy; D011284:Pregnenolone / Q000096:biosynthesis; D011359:Proestrus; D011374:Progesterone / Q000096:biosynthesis; D051381:Rats; D011919:Rats, Inbred Strains; D013254:Steroid 17-alpha-Hydroxylase / Q000378:metabolism
D011374:Progesterone; D004958:Estradiol; D011284:Pregnenolone; D007986:Luteinizing Hormone; D001141:Aromatase; D013254:Steroid 17-alpha-Hydroxylase; D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase; D000446:Aldehyde-Lyases; D010424:Pentobarbital