Effect of Prostaglandin F2α on the Number of LH Receptors in Ovine Corpora Lutea

Abstract

An experiment was conducted to determine if injections of prostaglandin (PG) F2 .alpha. influenced the number of receptors for LH [lutropin] in ovine luteal tissue and to compare the time course of change in the numbers of LH receptors and progesterone secretion. Ewes on day 9 of the estrous cycle were given 2 injections of PGF2 .alpha.-tham salt (6.7 mg, i.m.) at 4 h intervals. Corpora lutea were removed from each of 6 ewes at 2.5, 7.5 and 22.5 h after the initial injection of PGF2 .alpha. and from 6 control ewes on day 10 of the cycle. Jugular blood samples for analysis of progesterone were collected at 20 min intervals for 1 h prior to treatment and at 0.5, 1 or 2 h intervals in ewes in which corpora lutea were collected at 2.5, 7.5 and 22.5 h after injection of PGF2 .alpha., respectively. Luteal wt, luteal progesterone concentrations and total number of luteal LH receptors and the number of receptors occupied by endogenous LH were determined. Serum concentrations of progesterone were not decreased at 2.5 h after the initial injection of PGF2 .alpha., but had decreased by 7.5 and 22.5 h (P < 0.01). There was no change in luteal wt, luteal concentration of progesterone, total number of LH receptors or the number of receptors occupied by LH at 2.5 or 7.5 h when compared to luteal tissue from control ewes. Each of these parameters had decreased by 22.5 h. The affinity of the receptor for LH did not differ at any of the times studied. Progesterone secretion by the corpus luteum after PGF2 .alpha. administration decreased well before (7.5 h) decreases in the number of occupied or unoccupied receptors for LH could be detected (22.5 h).