Anovulatory Menstrual Cycles in the Rhesus Monkey: The Significance of Serum Follicle-Stimulating Hormone/Luteinizing Hormone Ratios

Abstract

Serum concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), 17β-estradiol, and progesterone were determined for samples collected daily from seven mature rhesus monkeys during anovulatory menstrual cycles. Menstrual cycles in four monkeys were characterized by (1) low serum FSH concentrations, (2) a remarkably stable pattern of FSH secretion throughout the cycle, (3) low serum estradiol concentrations which varied little during the intermenstrual interval, and (4) low serum LH concentrations. Two monkeys had high serum FSH concentrations without the normal postmenstrual pattern of declining FSH concentrations to a preovulatory nadir. Estradiol concentrations increased progressively from 70 to 193 pg/ml over the first 18 days of the cycle in one monkey with high FSH levels and then sharply declined, suggesting follicular atresia. The seventh monkey had normal serum FSH levels, a normal pattern of FSH secretion, and normal FSH. LH ratios. The serum estradiol level in this animal increased from 62 to 327 pg/ml over the first 11 days of the menstrual cycle and then declined precipitously without a surge in gonadotropins, suggesting a functional deficiency at the hypothalamic or pituitary level. These data, taken in concert with our previous observations on abnormal corpus luteum function in the rhesus monkey, illustrate that the optimal growth, maturation, ovulation, and luteinization of the follicle are dependent upon (1) sufficient concentrations of both FSH and LH in the serum, (2) an appropriate pattern of FSH secretion, (3) an appropriate ratio of serum FSH:LH, and (4) an ovulatory surge of gonadotropins.