Regulation of Gonadotropin Release by Luteinizing Hormone-Releasing Hormone and Estrogen in Chimpanzees*

Plasma LH and FSH levels were determined by RIA before and after an iv bolus of LHRH in adult female chimpanzees. The pre-LHRH concentration of 17β-estradiol (E2) was determined by RIA. Menstruating and postpartum chimpanzees (mean E2, 29.8 and 45.0 pg/ml, respectively) showed a monophasic LH response characterized by a 2- to 3-fold increase in LH levels within 15 min of LHRH injection, followed by a slow decline. In animals which had elevated estrogen levels, namely midfollicular animals (mean E2, 73.6 pg/ml), menstruating animals pretreated with 5 /μg estradiol benzoate for 2 days (mean E2, 283.2 pg/ml), and postpartum chimpanzees administered 50 μg mestranol/day for 7 days, LH showed a reduced or similar initial rise, followed by a plateau or slight decline during the first 60 min after LHRH but, thereafter, a progressive secondary increase that continued throughout the second 60 min. This secondary augmentation was greatly exaggerated when a long acting LHRH analog (desGly10-[D-Trp6, Pro9, NEt]LHRH) w...