title: Ovarian C17,20-lyase: changes in intact and hypophysectomized immature rats treated with pregnant mare's serum gonadotropin.
abstract: The steroid C17,20-lyase activity of immature rat ovarian microsomal (105,000 g pellet), mitochondrial (10,000 g pellet) and combined fractions was measured using progesterone and 17-hydroxyprogesterone as substrates. Steroid 17 alpha-hydroxylase was measured, using progesterone as substrate, in some of the preparations for comparison. With progesterone about 3.5 times more product (acetic acid) was formed than with 17-hydroxyprogesterone as substrate. The half-time for lyase activity following hypophysectomy was 51.8 h, while that for 17 alpha-hydroxylase was 51.3 h. Following an intravenous injection of 20 iu of pregnant mare's serum gonadotropin (PMS) into immature hypophysectomized rats lyase activity decreased for 12 h followed by recovery during the next 12 h with a rapid increase between 24 and 72 h. In contrast, a subcutaneous injection of the same dose produced an initial rise in activity with a decline between 12 and 24 h, followed by a second large increase. In intact animals injection (s.c.) of PMS produced an initial fall in lyase activity followed by an increase beginning 12 h later. A dramatic decrease in activity occurred between 48 and 72 h concomitant with ovulation; hypophysectomy at 48 h not only prevented the decrease, but produced an increase in activity. The changes in ovarian C17,20-lyase activity following administration of PMS mimic those of 17 alpha-hydroxylase.
mesh_terms: D000446:Aldehyde-Lyases / Q000378:metabolism*; D000818:Animals; D005260:Female; D006064:Gonadotropins, Equine / Q000494:pharmacology*; D007016:Hypophysectomy; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology; D008928:Mitochondria / Q000201:enzymology; D010053:Ovary / Q000187:drug effects / Q000201:enzymology*; D011374:Progesterone / Q000378:metabolism; D051381:Rats; D012741:Sexual Maturation; D013254:Steroid 17-alpha-Hydroxylase / Q000378:metabolism
chemical_list: D006064:Gonadotropins, Equine; D011374:Progesterone; D013254:Steroid 17-alpha-Hydroxylase; D000446:Aldehyde-Lyases