Insulin binding to monocytes and in vivo peripheral insulin sensitivity are normal in Graves’ disease

Insulin resistance in hyperthyroidism seems to depend on increased glucose production rather than on decreased glucose utilization. A decreased insulin binding on different target cells has been reported in patients in whom an in vivo evaluation of peripheral insulin sensitivity was lacking. In 20 patients with Graves’ disease (6 males, 14 females), aged 40.0 ± 2.0 yr, BMI 23.7 ± 0.7, and in 20 well-matched controls we performed the following tests: 75 g o.G.T.T., euglycemic-hyperinsulinemic clamp at 50 μU/ml combined with D-[3-3H] glucose infusion in tracer amounts, in vitro insulin binding on circulating monocytes. Fasting plasma glucose values were similar in the two groups, whereas plasma insulin values were significantly higher in hyperthyroids (21.4 ± 2.5 vs 10.6 ± 0.6 μU/ml, p < 0.01). The values of peripheral glucose utilization (5.61 ± 0.24 vs 6.01 ± 0.22 mg/kg-min) and of total specific insulin binding (4.07 ± 0.20 vs 4.39 ± 0.23 % bound to 10⁷ cells/ml) were not significantly different in the two groups. These results indicate that in vitro and in vivo data, when recorded in the same patients, are concordant to confirm a normal peripheral tissue sensitivity to insulin in Graves’ disease.