title: Human chorionic gonadotropin blocks the estrogen-induced luteinizing hormone release in long-term castrated rhesus monkeys: evidence for an ultrashort-loop negative feedback.
abstract: We studied the effects of human chorionic gonadotropin (hCG) administration on the biphasic response of luteinizing hormone (LH) to estrogen challenge in long-term castrated, female rhesus monkeys. Estradiol benzoate (EB), 400 micrograms, was administered to all animals at time zero; hCG, 2000 IU, was administered either concomitantly or 12 hours after EB. Blood samples were obtained every 6 hours for 58 hours, and then at 72 and 82 hours. Control animals received EB alone. Serum LH and beta hCG were determined by radioimmunoassay. Control animals showed a typical biphasic response to EB: an initial decrease in LH levels, 50% to 70% of baseline, from +6 hours until +30 hours; then a large increase, 150% to 190% of baseline, at +48 hours. Animals treated with hCG at time zero showed an initial decrease in LH, 40% to 70% of baseline, but LH returned to basal levels at +42 hours. Animals treated with hCG 12 hours after EB showed an initial decrease in LH, 45% to 55% of baseline, but LH returned to basal levels at +36 hours. These results suggest that an LH ultrashort-loop negative feedback may exist in the nonhuman primate.
mesh_terms: D000818:Animals; D002369:Castration; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D004967:Estrogens / Q000494:pharmacology*; D005246:Feedback; D005260:Female; D007986:Luteinizing Hormone / Q000378:metabolism*; D008253:Macaca mulatta; D013997:Time Factors
chemical_list: D006063:Chorionic Gonadotropin; D004967:Estrogens; D007986:Luteinizing Hormone