Down-regulation of pituitary gonadotropin secretion in postmenopausal females by continuous gonadotropin-releasing hormone administration.

Four normal postmenopausal females were infused with synthetic gonadotropin-releasing hormone (GnRH) iv at a rate of 1 microgram/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 mIU/ml, respectively, to peak values of 50 +/- 5 and 145 +/- 9 mIU/ml at 12 h. Serum LH then fell progressively toward basal levels during the continued iv administration of GnRH. Serum FSH fell below basal levels and remained suppressed between 36-72 h of the study period. Serum estradiol remained at levels less than 25 pg/ml throughout the GnRH infusion. Studies of LH and FSH secretion during the continuous administration of GnRH may be a useful model with which to study paradoxical down-regulation of pituitary gonadotropin secretion.