Hormonal modulation of structural alteration of rat ovarian luteinizing/human chorionic gonadotropin receptors

The structure-stabilizing effect of homologous and heterogeneous desensitiz ation and albumin on rat ovarian LH/hCG receptors was analyzed by thermal p erturbation technique. HCG-induced down-regulation shifted the heat inactiv ation profile of hCG-binding sites to a temperature lower by about 7 degree sC (T-50 values). In heterogeneous desensitization, which also involves unc oupling of receptors from adenylyl cyclase system, only follicle stimulatin g hormone (FSH) changed the stability of ovarian LH/hCG receptors. Stimulat ion of other hormonal receptors, which belong to the family of membrane spa nning G protein-linked receptors, i.e. beta -adrenergic, glucagon, serotoni n and prostaglandin E (PGE) had no effect on the stability of the LH/hCG re ceptor. Reduction of the stability of the LH/hCG receptor by about 3 degree sC after PGF(2 alpha) injection to luteinized rats may be connected with sp ecific process of luteolysis. On the other hand, albumin had a stabilizing effect on the receptor. The receptor destabilizing action of oleic acid inc orporated into ovarian membranes along with calcium stimulation of endogeno us phospholipase A (PLA) activity and reversal of these effects when BSA wa s used as fatty acid scavenger, may indicate that free fatty acids are resp onsible for the thermal instability of hCG-binding sites. Fluorescence quen ching studies indicated that extraction of free fatty acids by albumin elev ated the accessibility of fluorophores for acrylamide, and suggest that mod ificated lipid-protein interactions may affect the stability of the LH/hCG receptor structure.