Luteal phase defects in the rhesus monkey: the significance of serum FSH:LH ratios

Luteal phases of an abbreviated duration or suboptimal progesterone secretion were identified in the rhesus monkey. Characterization of menstrual cycles with short luteal phases (8 days) in 5 monkeys revealed the following deviations from normal: a. a failure of serum FSH to decline progressively from an early follicular phase high to a preovulatory nadir; b. a commonly inadequate, or absent, preovulatory FSH surge; c. subnormal serum LH concentrations during both the follicular and luteal portions of the menstrual cycle; d. ratios of serum FSH:LH which did not progressively decrease during the follicular phase; and e. serum estradiol concentrations below normal values during the luteal portion of the menstrual cycle. One monkey had abnormally low serum concentrations of progesterone, although the luteal phase was 19 days in duration. Serum gonadotropin and estradiol patterns in this latter monkey were identical to those observed in monkeys with short luteal phases. It is concluded that inappropriate ratios of serum FSH:LH during the follicular phase of the menstrual cycle result in impaired corpus leteum function. The data document the usefulness of the nonhuman primate for investigating those luteal phase defects which also occur in the woman.