Effect of hCG on the 13,14-dihydro-prostaglandin F2-alpha forming capacity of the ovary after ovulation in PMSG-primed immature female rats

We have examined the change in the ovarian 13,14-dihydro-prostaglandin F2 alpha (13,14H2-PGF2 alpha) forming capacity after the first ovulation induced by injection of pregnant mare serum gonadotropin (PMSG 5 IU, sc) at 26 days of age. After ovulation, the 13,14H2-PGF2 alpha forming capacity in the whole ovary (WO) and in non-luteal ovarian tissues (WO-CL) gradually decreased, whereas a rapid decrease of the synthesizing capacity was observed in corpus luteum (CL). The capacity in WO 4 days after ovulation (33 days of age) was markedly stimulated by human chorionic gonadotropin (hCG 10 IU, ip) administration, whereas CL at 33 days of age did not respond to the stimulatory effect of hCG. A single injection of hCG on day 7 after hypophysectomy resulted 12 hrs later in a significant increase in the forming capacity of 13,14H2-PGF2 alpha in WO-CL. These results indicate that the 13,14H2-PGF2 alpha forming capacity in CL rapidly decreases after the first ovulation and the WO-CL, but not CL, retain the ability to form 13,14H2-PGF2 alpha in response to exogenous gonadotropin for a long time.