Prevention of the postcoital luteinizing hormone surge by ultrashortloop feedback control.

Studies were designed to determine whether the ultrashortloop feedback (USLF) system could prevent the gonadotropin-releasing hormone (GnRH) stimulation and postcoital rise of luteinizing hormone (LH). Unanesthetized castrated female rabbits bearing chronically-implanted venous catheters were subjected to the following: (1) GnRH stimulation. Ten animals received intravenous (IV) bolus injections of 30 microgram GnRH. Two hours prior to GnRH, animals received either 2000 IU human chorionic gonadotropin (hCG) or saline. A second group of ten animals received 20 microgram GnRH. One hour prior to GnRH, an infusion of human luteinizing hormone (hLH) at 2.75 IU/min or of saline was started and continued over 4 hours. (2) Coital stimulation. Ten rabbits were studied with the use of natural coital stimulus. They received either 2000 IU hCG 2 hours before mating or saline as a control group. Both hLH infusion and hCG injection inhibited GnRH stimulation of LH secretion but did not modify the follicle-stimulating hormone (FSH) response. hCG inhibited the coitus-induced LH surge and did not modify coitus-induced FSH secretion. These studies demonstrate that USLF control of LH can modulate LH secretion under both pharmacologic and physiologic conditions.