Demonstration of Luteinizing Hormone/Human Chorionic Gonadotrophin Receptor-Binding Inhibitor in Aqueous Extracts of Frozen Human Corpus Luteum

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Abstract
Aqueous extracts of frozen human corpora lutea were tested for the presence of an inhibitor of luteinizing hormone[lutropin]-receptor site binding (LHRBI) and for the subsequent effect on the stimulatory response of LH on progesterone synthesis by sheep ovarian cells. In the presence of human corpus luteum extract of normal menstrual cycle (30,000 g supernatant), the binding of 125I human chorionic gonadotropin (hCG) to granulosa and luteal cells of sheep ovaries was markedly reduced, but the ability of rat testicular LH receptors to bind labeled hCG was less affected. Extracts of corpora lutea of the 1st trimester of pregnancy appeared to be less inhibitory on the binding of LH/hCG to ovarian cells and had no effect on the binding of rat testicular cells compared to those of normal menstrual cycle. Addition of both extracts separately inhibited the LH-stimulated in vitro progesterone synthesis by granulosa cell cultures and by incubated sheep corpus luteum slices. Evidently LHRBI is present in human corpus luteum.

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