DIRECT ACTION OF MELATONIN ON HEN OVARIAN GRANULOSA-CELLS TO LOWER RESPONSIVENESS TO LUTEINIZING-HORMONE

The presence of a melatonin-binding component in the membrane fraction of the ovarian granulosa cells of hens that has characteristics of a receptor such as high affinity, limited capacity, reversible binding, and binding specificity was demonstrated by radioligand binding assays , When the cells were incubated in vitro with various concentrations o f luteinizing hormone (LH) in the presence and absence of melatonin (1 and 5 nM), the dose-response curve for the LH-stimulated progesterone production was shifted to a higher concentration of LH: ED50 of LH wa s approximately two times greater in the presence of melatonin, The re sults suggest a direct action of melatonin on the ovarian granulosa ce lls of the hen to lower the responsiveness to LH for progesterone prod uction.