COMPARISON OF ESTIMATES OF INSULIN SENSITIVITY IN PREMENOPAUSAL AND POSTMENOPAUSAL WOMEN USING THE INSULIN TOLERANCE-TEST AND THE FREQUENTLY SAMPLED INTRAVENOUS GLUCOSE-TOLERANCE TEST

OBJECTIVE: We assessed insulin sensitivity in women comparing the insu lin tolerance test (ITT) with the intravenous glucose tolerance test w ith frequent sampling and computer modeling (FSIVGTT) and evaluated th e effects of hormonal therapy in postmenopausal women using both metho ds. METHODS: This prospective study tested 18 premenopausal women and ten postmenopausal women randomized to receive either estrogen alone o r estrogen with a sequential progestin for 6 months at a menopause res earch clinic. All subjects received an ITT and an FSIVGTT within 48-72 hours of each other in random sequence. Postmenopausal women were the n randomized to receive either 0.625 mg conjugated equine estrogen for 6 months or 0.625 mg conjugated equine estrogen with medroxyprogester one acetate, 10 mg, for 10 days each month for 6 months. Both the ITT and the FSIVGTT were repeated following hormonal therapy at 2 and 6 mo nths. Plasma insulin and glucose were measured; insulin sensitivity wa s calculated after the ITT (Kitt) and the FSIVGTT (Si) at each visit i n each group. RESULTS: A close correlation was found between Kitt and Si values at initial testing in both pre- and postmenopausal women and following both types of hormonal therapy (r = 0.76 for all tests, P < .001). A reduction in insulin sensitivity was observed in postmenopau sal compared to premenopausal women; this occurred in five of ten post menopausal women using the Kitt measurement and in four of ten women u sing Si. Estrogen replacement had a beneficial effect on insulin sensi tivity. While Kitt increases by 24.2+/-9.6% (P < .05), the increase in Si (6.7+/-18%) was not significant because of the variability with th is measurement. An attenuation in insulin sensitivity was seen with ad ded progestin. Kitt values decreased by 17.7+/-7.7% and Si values by 3 1.9+/-12%. Similar findings were noted at 2 and 6 months. CONCLUSIONS: The ITT and FSIVGTT provide quantitatively similar information regard ing insulin sensitivity in healthy women. A mild degree of insulin res istance appears to be present in some healthy postmenopausal women. Es trogen appears to improve insulin sensitivity, while added progestin m ay attenuate this beneficial effect.