Modulation of LH/hCG receptors and physical state of ovarian membranes in rat pseudopregnancy.

Previous investigations have demonstrated that increased ovarian function during pseudopregnancy in the rat may be associated with alterations of the physical state of membranes. Changes in rigidity of membrane lipids were observed during the formation as well as regression of corpora lutea. The effects of cyclooxygenase inhibitors (indomethacin and acetylsalicylic acid (ASA)) and of selected steroids (estradiol, testosterone and dihydrotestosterone) on the functional state of luteinized ovaries were studied. The compounds were administered to the animals in silastic capsules on different days after hCG injection. ASA and indomethacin administration on days 10 and 11 after hCG injection resulted in an increase in the LH/hCG receptor binding activity and rigidity of ovarian membrane lipids, as determined by fluorescence polarization of 1,6-diphenyl-1,3,5 hexatriene (DPH) probe. This effect was apparent within 7 days after indomethacin and ASA treatment. Both estradiol and testosterone significantly increased the ovarian LH/hCG binding activity, however estradiol did not affect the membrane lipid rigidity. Unlike testosterone, the administration of dihydrotestosterone induced a decrease in membrane lipid rigidity and reduced the accessibility of the LH/hCG receptor. Inhibitors of prostaglandin F2alpha (PGF2alpha) synthesis, as the endogenous mediator of luteolysis, were shown to delay the regression of the corpora lutea and to prolong the luteal activity in pseudopregnant rats.