Caloric restriction inhibits steroid-induced gonadotropin surges in ovariectomized rhesus monkeys

We recently reported that caloric restriction inhibited ovulation in rhesus monkeys. The objective of the current study was to determine if caloric restriction affected the positive feedback response to ovarian steroids in non-human primates. Studies were conducted in four long-term ovariectomized rhesus monkeys. Animals were given an estrogen/progesterone challenge while maintained on a normal diet and on a diet that reduced body weight by approx 20%. In all cases, animals were maintained at the desired weight [based on a calculation of body mass index (BMI)] for a minimum of 4 wk before initiating the steroid challenge. Caloric restriction reduced BMI from 23.3±0.3 to 18.9±0.2 kg/m². The estrogen/progesterone challenge elicited an LH and FSH surge in each animal maintained at a normal BMI. By contrast, gonadotropin surges were significantly compromised when monkeys were challenged at a low BMI. In addition to affecting the reproductive axis, caloric restriction stimulated cortisol release and suppressed T₃ secretion. These endocrine effects of caloric restriction are consistent with our findings in ovary-intact monkeys. In summary, our previous reports in ovary-intact animals confirmed an effect of caloric restriction on tonic gonadotropin secretion leading to anovulation. Our current results suggest the effects of caloric restriction on the reproductive axis extend beyond inhibition of tonic gonadotropin secretion to include a disturbance of phasic gonadotropin secretion.