Down-Regulation of Pituitary Gonadotropin Secretion in Postmenopausal Females by Continuous Gonadotropin-Releasing Hormone Administration*

Abstract

Four normal postmenopausal females were infused with synthetic gonadotropin−releasinghormone (GnRH) iv at a rate of 1 ⁄xg⁄min for 72 h. Serum LH, FSH, and estradiol were measured every 4 h. LH and FSH levels increased from basal values of 23 ° 3 and 94° 27 mlU⁄ml, respectively, to peak values of 50 ° 5 and 145 ° 9 mlU⁄ml at 12 h. Serum LH then fellprogressively toward basallevels during the continued iv administration of GnRH. Serum FSH fell below basal levels and remained suppressed between 36−72 hof the study period. Serum estradiol remained at levels less than 25pg⁄ml throughout the GnRH infusion. Studies of LH and FSHsecretion during the continuous administration of GnRH may be a useful model with which to study paradoxical down−regulation of pituitarygonad