Objective: Limited data are available on the effects of the menstrual cycle on the hypothalamic-pituitary-adrenal axis (HPA) function. This study evaluates HPA axis reactivity to insulin-induced hypoglycaemia over the menstrual cycle.
Patients: Twelve normal women were randomized to placebo and evaluated during three successive menstrual cycles. Menstrual phase was documented by menstrual diary and by oestradiol and progesterone levels at the time of each insulin tolerance test (ITT). Six normal men were included as a comparison in the statistical analysis.
Measurements: Afternoon ITTs were performed initially on the second or third day of menses in women, then seven more ITTs followed at one or two week intervals during the next 10 weeks. Serum measurements of glucose, adrenocorticotrophin (ACTH) and cortisol were obtained.
Results: The glucose and ACTH responses to the ITTs were similar between men and women. Cortisol levels at baseline and during the test were higher in men than in women, although the amount of change was similar. Glucose, ACTH and cortisol response to insulin-induced hypoglycaemia did not vary over the menstrual cycle or during repeat testing in men or women.
Conclusions: These data show that it is unnecessary to control for menstrual cycle during insulin tolerance tests performed at 1600 hours. It is, however, necessary to control for the effect of sex on cortisol levels. Repeat testing more than one week apart does not appear to influence the glucose, ACTH or cortisol response to insulin stress.