Prostaglandins Do Not Appear to Play a Role in hCG-Induced Regression or Desensitization of Rabbit Corpora Lutea1

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Abstract
Prostaglandin [PG] F2.alpha. has been suggested to be a physiological luteolysin in several species. This study determined whether PG are involved in the hCG[human chorionic gonadotropin]-induced desensitization of the luteal LH[luteinizing hormone]-responsive adenylate cyclase or hCG-induced luteal regression. Rabbits were made pseudopregnant by injection of 75 IU of hCG (day 0 of pseudopregnancy). Rabbits (n = 34) were surgically implanted with estradiol-filled Silastic capsules or empty capsules on day 5 of pseudopregnancy. Other rabbits (n = 16) did not receive implants of any kind. On day 6 of pseudopregnancy, all rabbits were injected with sesame oil or indomethacin (70 mg) at 1000 h and with saline or hCG (75 IU) at 1600 h; at 1800 h, the oil and indomethacin injections were repeated. At 1000 h on day 7 of pseudopregnancy (18 h after injection with hCG or saline), the rabbits without implants were killed, blood was collected by cardiac puncture, and the ovaries were removed and corpora lutea dissected free. Luteal homogenates were assayed for adenylate cyclase activity and progesterone [P] content, and the serum obtained was assayed for P. Blood was drawn at 1600 h (24 h after hCG or saline treatment) from the rabbits with estradiol-filled or empty implants. The serum obtained was assayed for P. Injection of hCG caused an increase in basal luteal adenylate cyclase activity but caused decreases in LH-, isoproterenol-, and NaF-stimulated luteal adenylate cyclase activities as well as a decrease in luteal P concentration. Indomethacin treatment alone had no major effect on any parameter measured, but did cause an attenuation of the increased basal adenylate cyclase activity found after hCG injection. Treatment with indomethacin did not prevent hCG-induced desensitization or luteal regression. Estradiol partially protected the corpora lutea from the hCG-induced decrease in serum progesterone.

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