IN-VIVO RESPONSES OF THE PRIMATE CORPUS-LUTEUM TO LUTEINIZING-HORMONEAND CHORIONIC-GONADOTROPIN

Although it is well established that the secretory activity of the cor pus luteum absolutely depends on the presence of pituitary-derived lut einizing hormone (LH), it is unknown why the life span of the corpus l uteum is extended during early pregnancy by the placental production o f chorionic gonadotropin (CG) but regresses in the presence of LH desp ite the fact that CG and LH have similar actions on the corpus luteum. To compare the responses of the corpus luteum to LH and human CG (hCG ), cynomolgus monkeys whose endogenous gonadotropin secretion was bloc ked during the luteal phase of the menstrual cycle with a gonadotropin -releasing hormone antagonist were i.v. infused with either LH or CG, Infusion of LH at a constant rate overcame the gonadotropin-releasing hormone antagonist-mediated premature luteal regression but failed to prolong the functional life span of the corpus luteum. Continuous infu sions of hCG did not effect a pregnancy-like pattern of gonadotropin s ecretion, but the functional life span of the corpus luteun was extend ed in two of three animals. Infusion of either LH or hCG in an exponen tially increasing manner prolonged the functional life span of the cor pus luteum beyond its normal duration, These results indicate that lut eal regression at the termination of nonfertile menstrual cycles is ca used by a large reduction in the responsiveness of the aging corpus lu teum to LH, which can be overcome by elevated concentrations of either LH or CG.