Changes in insulin sensitivity, secretion and glucose effectiveness duringmenstrual cycle

Background. Several clinical conditions suggest an effect of sex steroids o n glucose homeostasis in women. Studies examining this phenomenon have yiel ded controversial results. Methods. To investigate the effect of the menstrual cycle on insulin sensit ivity, glucose effectiveness and acute insulin response to glucose using th e tolbutamide-modified intravenous glucose tolerance test (IVGTT) during th e follicular (day 8 +/- 1) and luteal (day 23 +/- 1) phases of the menstrua l cycle, the authors recruited 12 healthy regularly menstruating women. All had fasting glucose concentration of <100 mu g/dl (89.7 +/- 6.2) with no f amily history of diabetes mellitus; their body mass indices were <25 kg/m(2 ) (22.41 +/- 1.44 kg/m(2)). Results. The mean insulin sensitivity (Si) values decreased during the cycl e. Insulin sensitivity (Si x 10(-4)/min.mU/ml) was higher in the follicular phase (5.03 +/- 0.72) and decreased in the luteal phase (2.22 +/- 0.45) (p <0.001), Glucose effectiveness (Sg min(-1)) did not change as a function o f the phase of the menstrual cycle, SE estimates were 0.0229 +/- 0.00323 in the follicular phase, and 0.0225 +/- 0.00319 (p = NS) in the luteal phase, respectively. Acute insulin response (AIRg mU/ml) was 276.4 +/- 27.8 in th e follicular phase. An adaptive increase (303.4 +/- 51.1) in response to th e insulin resistance during the luteal phase was observed, but this increas e was not statistically significant (p = NS). Conclusions. Knowledge of the variations in insulin sensitivity that occur during the normal menstrual cycle provides a basis of comparison for studie s of other clinical conditions, Also, this phenomenon should be considered if the determination of insulin resistance is the purpose of certain epidem iological studies. (C) 1999 IMSS, Published by Elsevier Science Inc.