LUTEOLYTIC ACTION OF PROSTAGLANDINS IN SWINE AND THE EFFECTS OF CLOPROSTENOL ON LUTEINIZING HORMONE RECEPTORS AND MEMBRANE STRUCTURE OF PORCINE CORPORA LUTEA

Abstract

The luteolytic action of prostaglandin F2α (PGF2α), 15-keto-PGF2α, 15-methyl-PGF2α, and cloprostenol was evaluated in cycling gilts and sows after intramuscular injection on day 13 of the estrous cycle. Only cloprostenol significantly shortened the mean cycle length (18.5 vs. 20.3 d, P < 0.05). Cloprostenol also caused a more rapid decline in serum progesterone concentrations than did the other prostaglandins. Serum concentrations of the prostaglandin metabolite 13,14-dihydro-15-keto-PGF2α (PGFM), showed rapid transitory peaks after PGF2α or 15-keto-PGF2α and a lower, later rise after cloprostenol. A second experiment examined luteal luteinizing hormone (LH) receptors and luteal membrane ultrastructure during the estrous cycle and pregnancy and the effect of cloprostenol on these parameters during the estrous cycle. The number of unoccupied luteal LH receptors, as measured by specific 125I-hCG binding, dropped significantly from mid to late pregnancy and from mid to late cycle. Cloprostenol lowered serum progesterone concentrations but did not affect hCG binding. X-ray diffraction showed no correlation of gel or liquid-crystalline phase lipids in luteal microsomes with the stage of the estrous cycle or pregnancy or cloprostenol treatment. Key words: Swine, luteolysis, estrous cycle, prostaglandins, luteal LH receptors