Luteinizing hormone (LH) and chorionic gonadotropin regulate the secretion of progesterone from the corpus luteum. Sheep luteal cells will be used for studying physical events accompanying human chorionic gonadotropin or ovine luteinizing hormone binding to the luteinizing hormone receptor. The goals of this research are to study luteinizing hormone receptor aggregation, distribution, and molecular motions on sheep luteal cells during the luteal phase of the estrous cycle and to study how the physical behavior of the receptor is affected by its interactions with the hormones. First, LH receptor aggregation will be examined on viable cells before and after hormone binding using fluorescence energy transfer and measurements of LH receptor rotational motions. Receptor distribution will be examined using computer-enhanced low light microscopy and electron microscopy. Second, the roles of the subunits of the hormones and of their associated carbohydrates in modifying lateral and rotational motions of hormone-occupied LH receptors will be determined. Third, cytoskeletal interactions with the LH receptor before and after hormone binding will be characterized. Finally, interactions of the hormone-occupied LH receptor with other luteal cell membrane proteins will be examined. Progesterone secretion from the corpus luteum is required to maintain uterine conditions for embryonic development in early pregnancy. LH and chorionic gonadotropin regulate progesterone secretion, but much remains to be learned about their cellular mechanisms of action. The proposed biophysical characterization of hormone-occupied receptors on the membranes of luteal cells and an analysis of the interactions of the hormone-receptor complex with other plasma membrane constituents is a first step in understanding the mechanisms by which these hormones regulate luteal cell function.
