Luteal steroidogenesis and regression in the rat: effects of human chorionic gonadotrophin and phospholipase A2 on cells and plasma membranes.

Progesterone production in vitro was measured in response to human chorionic gonadotrophin and phospholipase A2 using dispersed luteal cells from control and prostaglandin F2 alpha (PGF2 alpha)-treated rats. Highly purified luteal plasma membrane suspensions were prepared by partition distribution in dextranpolyethylene glycol, and membrane fluidity was measured by fluorescence polarization using the probe, trans-parinaric acid. Fluorescence polarization was highly dependent upon calcium, and was markedly affected by PGF2 alpha treatment. No support was found for the theory that bulk membrane fluidity has a role in receptor or enzyme hindrance in the induction of luteal cell regression. However, membrane phase transitions induced by calcium interaction with anionic phospholipids and free radical damage may be involved in regression of the rat corpus luteum.