DEPRESSION OF FSH AND LH-SECRETION FOLLOWING PULSATILE GNRH ADMINISTRATION IN OVARIECTOMIZED WOMEN

To investigate the mechanism by which pulsatile administration of gona dotrophin-releasing hormone (GnRH) modifies secretion of luteinizing h ormone (LH) and follicle-stimulating hormone (FSH), we studied three g roups of five women who had been ovariectomized for non-malignant gyna ecological conditions at least 6 months previously, none of whom had r eceived substitutional hormone therapy. Before and after 15 day treatm ent with subcutaneous pulsatile GnRH tone 20 mu g dose every 90 min in group A, one 10 mu g dose every 90 min in group B and one 20 mu g dos e every 120 min in group C), pulsatile secretion of LH and FSH was cha racterized by determining these hormones in 4 mi blood samples taken e very 10 min for 8 h (9.00 a.m. to 5.00 p.m.). For both LH and FSH, mea n serum concentration and pulse amplitude were lower after GnRH treatm ent than before land in the case of LH the decrease depended upon both the size and frequency of exogenous GnRH pulses) but in no group was there a significant change in LH or FSH pulse frequency, We conclude t hat exogenous pulsatile GnRH probably acts by partially desensitizing the pituitary rather than by depressing endogenous GnRH secretion. Suc h partial desensitization would explain reports that exogenous pulsati le GnRH improves ovulation by women with polycystic ovary syndrome.