LUTEINIZING-HORMONE RECEPTORS AND PROGESTERONE CONTENT IN PORCINE CORPORA-LUTEA AFTER PROSTAGLANDIN-F2-ALPHA

The effect of prostaglandin F2.alpha. (PGF2.alpha.) on luteinizing hormone (LH) receptors, weight and progesterone content of corpora lutea (CL), and serum progesterone concentrations was studied in gilts. Fifteen gilts were hysterectomized between Days 9 to 11 of the estrous cycle. Twelve gilts were injected i.m. with 10 mg of PGF2.alpha. and 3 with saline on Day 20. Ovaries were surgically removed from each of 3 gilts at 4, 8, 12 and 24 h following PGF2.alpha. treatment and from the 3 control gilts 12 h following saline injection. Jugular blood samples for progesterone analysis were collected from all gilts at 0, 2 and 4 h following treatment and at 8, 12 and 24 h for gilts from which ovaries were removed at 8, 12 and 24 h, respectively. Mean serum progesterone and CL progesterone concentrations decreased within 4 h after PGF2.alpha. treatment (P < 0.05) and remained low through 24 h after treatment. The number of unoccupied LH receptors decreased by 4 h (P < 0.05) and this trend continued through 24 h. There were no differences in luteal weight or affinity of unoccupied LH receptors of luteal tissue at 4, 8, 12 and 24 h after PGF2.alpha. when compared to luteal tissue from controls. During PGF2.alpha.-induced luteolysis in the pig, luteal progesterone, serum progesterone concentrations and the number of LH receptors decrease simultaneously.