J. Kolena et al., Hormonal modulation of structural alteration of rat ovarian luteinizing/human chorionic gonadotropin receptors, GEN PHYSL B, 19(3), 2000, pp. 295-303
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.