Insulin sensitivity, metabolic clearance rate of insulin (MCR-I) and basal posthepatic insulin delivery rate (BIDR) were investigated by means of euglycemic clamp technique in 8 normal subjects and 8 patients with hyperthyroid Graves' disease. The mean (±SD) steady-state glucose infusion rate (SSGIR) was lower in hyperthyroid Graves' patients than in normal subjects (228.9±57.0 vs. 290.9±49.4 mg/m²/min, p<0.05). Both MCR-I and BIDR were higher in hyperthyroid Graves' patients than in normal subjects (1162.9±517.1 vs. 463.5±103.9 ml/m²/min, p<0.005; 17.7±12.6 vs. 3.6±0.9 mU/m²/min, p<0.01, respectively). Plasma free T₄ levels showed a close correlation with MCR-I (r=0.77, p<0.05) and BIDR (r=0.81, p<0.05), respectively, in Graves' patients. These findings indicate that hyperthyroidism is characterized by not only a decrease in insulin sensitivity, but also an increase in basal insulin secretion and the metabolic clearance rate of insulin, which are correlated with plasma free T₄ levels.
(Internal Medicine 34: 339-341, 1995)