DIETARY RESTRICTION REDUCES LUTEINIZING-HORMONE (LH) PULSE FREQUENCY DURING WAKING HOURS AND INCREASES LH PULSE AMPLITUDE DURING SLEEP IN YOUNG MENSTRUATING WOMEN

To determine the effect of dietary energy restriction on gonadotropins, we assayed LH and FSH in samples drawn at 10- and 60-min intervals, respectively, over 24 h from seven young women (mean +/- SE gynecological age, 7.7 +/- 1.2 yr) on day 9, 10, or 11 of two menstrual cycles. Cortisol was measured in samples collected at 30-min intervals. During the 4 previous days and the day of sampling, dietary energy intake was set at either 45 or 10 Cal/kg lean body mass day in random order. Beginning 2 days before treatment, blood was sampled daily at 0800 h and assayed for TB, insulin-like growth factor-I, and insulin. Estradiol was measured in samples collected daily and at 6-h intervals on the day of frequent sampling. By the day of frequent sampling, dietary restriction had reduced T-3 20% (P < 0.01), insulin-like growth factor-I 58% (P < 0.001), and insulin 54% (P < 0.001). Twenty-four-hour transverse means for LH (P = 0.3), FSH (P = 0.2), estradiol (P = 0.3), and cortisol (P = 0.13) were unaffected, but LH pulse frequency was reduced 23% (P < 0.01), especially during waking hours, whereas LH pulse amplitude was increased 40% (P = 0.05), especially during sleep. These results support the hypothesis that LH pulsatility depends upon energy availability in women, as it does in other mammalian species.