Insulin sensitivity in women: a comparison among values derived from intravenous glucose tolerance tests with different sampling frequency, oral glucose tolerance test or fasting.

OBJECTIVE: To determine the correlation between insulin sensitivity (S(I)) obtained by the minimal model method applied to a frequently sampled (n=33) intravenous glucose tolerance test (FSIGT(33)), and values obtained by reduced FSIGTs, oral glucose tolerance test (OGTT), or fasting. DESIGN: Retrospective analysis on tests performed in prospective studies. METHODS: A total of 78 FSIGT(33), and 59 OGTT were performed in non-diabetic women of which 10 were young cyclic females in the early follicular menstrual phase, 10 were young non-obese subjects with polycystic ovary syndrome (PCOS) and 30 were in post-menopause. Some of these individuals were investigated both prior to and during specified treatments. FSIGT(33) was transformed into FSIGT(22) and FSIGT(12) by removing samples from the analysis. Values of SI derived from reduced FSIGTs or calculations performed on glucose and insulin values observed in fasting conditions and/or during OGTT were related to those of FSIGT(33). RESULTS: S(I) values derived from FSIGT(33) were highly correlated with those derived from FSIGT(22) (r=0.965) or FSIGT(12) (r=0.955), but were only weakly correlated with those derived from fasting or OGTT calculations (r below 0.5). Between-group (PCOS vs normal) or within-group (prior to and during treatment) comparisons showed that reduced FSIGTs were only slightly less powerful than FSIGT(33) in detecting differences in S(I). CONCLUSIONS: In non-diabetic women, reduced FSIGTs but not calculations based on fasting or OGTT values may be used in place of FSIGT(33) to document S(I) and its variation.

Influence of melatonin administration on glucose tolerance and insulin sensitivity of postmenopausal women.

OBJECTIVE: The effect of melatonin on human carbohydrate metabolism is not yet clear. We investigated whether melatonin influences glucose tolerance and insulin sensitivity in aged women. PATIENTS: Twenty-two postmenopausal women of whom 14 were on hormone replacement therapy. DESIGN: After an overnight fast, at 0800 hours on two nonconsecutive days, placebo or melatonin (1 mg) were administered randomly and in a double blind fashion. Forty-five minutes later, an oral glucose tolerance test (75 g; OGTT) was performed in 13 women. In another nine women insulin-dependent (Si) and -independent (Sg) glucose utilization was tested by a frequently sampled intravenous glucose tolerance test (FSIGT). RESULTS: Areas under the response curve to OGTT (AUC) for glucose (1420 +/- 59 vs. 1250 +/- 55 mmol x min/l; P < 0.01), and C-peptide (42,0980 +/- 45,320 vs. 33,528 +/- 15,779 pmol x min/l; P < 0.02) were higher following melatonin than placebo, while Si values were lower (2.6 +/- 0.28 units vs. 3.49 +/- 0.4 units; P < 0.03). Si modifications induced by melatonin were inversely related to Si values of the placebo day (r(2) = 0.538; P < 0.025). CONCLUSIONS: The present results indicate that in aged women administration of 1 mg of melatonin reduces glucose tolerance and insulin sensitivity. The present data may have both physiological and clinical implications.