Insulin Sensitivity during the Menstrual Cycle*

Sensitivity to insulin (euglycemic clamp technique) and serum estradiol and progesterone levels were measured in seven normal nonobese women, aged 19-23 yr, during the follicular and luteal phases of the menstrual cycle. The mean serum progesterone level was 1.2 +/- 0.1 (+/- SE) nmol/liter in the follicular and 24.2 +/- 7.7 nmol/liter in the luteal phase (P less than 0.02). Mean plasma insulin was maintained at 84 +/- 6 and 86 +/- 3 mU/liter and mean plasma glucose at 4.6 +/- 0.1 and 4.6 +/- 0.1 mmol/liter during the insulin clamps in the follicular and luteal phases, respectively. The rate of glucose metabolism averaged 9.0 +/- 1.3 mg/kg X min in the follicular phase and 9.2 +/- 1.6 mg/kg X min (P = NS) during the luteal phase. These results indicate that insulin-mediated glucose metabolism, as determined by the euglycemic clamp technique, is unaffected by the phase of the menstrual cycle in normal women.