Early hCG-induced desensitization of rat ovarian LH/hCG receptors is associated with altered physical state of membranes.

Injection of pseudopregnant rats with pharmacological doses of hCG produced desensitization of adenylylcyclase and steroidogenic systems in ovarian membranes and luteal cells. Membrane lipid rigidity, as determined by fluorescence polarization of DPH, decreased as early as 0.5 h after injection of hCG. Desensitization also modified the differential scanning calorimetric profile characteristic of control membranes. The accessibility of ovarian LH/hCG receptors was unchanged. The results indicate that the hCG-induced decrease of membrane lipid rigidity is preceded by the process of desensitization of the rat ovary.