Abstract
Prostaglandin F2α has been suggested to be a physiological luteolysin in several species. It was the intent of the study reported herein to determine whether prostaglandins are involved in the hCG-induced desensitization of the luteal LH-responsive adenylyl 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 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 lutes dissected free. Luteal homogenates were assayed for adenylyl cyclase activity and progesterone content, and the serum obtained was assayed for progesterone. 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 progesterone. Injection of hCG caused an increase in basal luteal adenylyl cyclase activity but caused decreases in LH-, isoproterenol-, and NaF-stimulated luteal adenylyl cyclase activities as well as a decrease in luteal progesterone concentration. Indomethacin treatment alone had no major effect on any parameter measured, but did cause an attenuation of the increased basal adenylyl cyclase activity found after hCG injection. Treatment with indomethacin did not prevent hCG-induced desensitization or luteal regression. Estradiol, on the other hand, partially protected the corpora lutea from the hCG-induced decrease in serum progesterone.
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