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Insulin binding to monocytes and in vivo peripheral insulin sensitivity are normal in Graves' disease
P Cavallo-Perin1, A Bruno, C Bozzo
1Istituto di Medicina Interna, Università di Torino, Italy.
Abstract:
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 microU/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 microU/ml, p less than 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 10(7) 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.
Insights
Hyperthyroidism may increase insulin resistance through higher glucose production, not reduced utilization. This study found normal peripheral insulin sensitivity in Graves' disease patients, challenging previous assumptions.
Area of Science:
- Endocrinology
- Metabolic Research
Background:
- Hyperthyroidism is associated with insulin resistance, potentially due to increased glucose production.
- Previous studies lacked in vivo evaluation of peripheral insulin sensitivity in hyperthyroid patients.
Purpose of the Study:
- To evaluate peripheral insulin sensitivity in patients with Graves' disease.
- To compare in vivo and in vitro insulin sensitivity data in hyperthyroid individuals.
Main Methods:
- 20 Graves' disease patients and 20 controls underwent oral glucose tolerance tests and euglycemic-hyperinsulinemic clamps.
- Tracer amounts of D-[3-3H] glucose were infused, and in vitro insulin binding on monocytes was assessed.
Main Results:
- Fasting glucose levels were similar, but insulin levels were higher in hyperthyroid patients.
- Peripheral glucose utilization and total specific insulin binding were not significantly different between groups.
Conclusions:
- In vivo and in vitro data confirm normal peripheral tissue sensitivity to insulin in Graves' disease.
- Insulin resistance in hyperthyroidism may stem from increased glucose production rather than impaired insulin action.