The effect of transdermal 17-beta-estradiol on glucose metabolism of postmenopausal women is evident during the oral but not the intravenous glucose administration

To evaluate the effect of transdermal 17-beta-estradiol (50 micrograms/day) on glucose metabolism of postmenopausal women.A frequently sampled intravenous glucose tolerance test (FSIGT), to calculate insulin sensitivity (SI) and peripheral glucose utilization independent of insulin (SG), and an oral glucose tolerance test (75 g; OGTT), were performed in nine postmenopausal women prior to, and after 2 months of, treatment.Estradiol decreased insulin and increased the C-peptide/insulin ratio both during fasting (P < 0.02) and OGTT (insulin levels, P < 0.01; C-peptide/insulin ratio, P < 0.05), but not FSIGT. Glucose levels, C-peptide levels, SI and SG were not affected.In spite of unmodified SI, the reduction of insulin levels and the increase of the C-peptide/insulin ratio, observed during fasting and OGTT, support a beneficial effect of estradiol on glucose metabolism. This effect probably requires the interplay of estradiol with gastrointestinal factors.