In hyperthyroidism, although hepatic insulin resistance is well established, information on the effects of insulin on glucose uptake in skeletal muscle is variable.Methods:
To investigate this, a meal was given to nine hyperthyroid (HR) and seven euthyroid (EU) subjects. Blood was withdrawn for 360 min from a forearm deep vein and the radial artery for measurements of insulin and glucose. Forearm blood flow (BF) was measured with strain-gauge plethysmography. Glucose flux was calculated as arteriovenous difference multiplied by BF and fractional glucose extraction as arteriovenous difference divided by arterial glucose concentrations.Results:
Both groups displayed comparable postprandial glucose levels, with the HR having higher insulin levels than the EU. In the forearm of HR vs. EU: 1) glucose flux was similar [area under the curve (AUC)0-360 673 ± 143 vs. 826 ± 157 μmol per 100 ml tissue]; 2) BF was increased (AUC0-360 3076 ± 338 vs. 1745 ± 145 ml per 100 ml tissue, P = 0.005); and 3) fractional glucose extraction was decreased (AUC0-360 14.5 ± 3 vs. 32 ± 5%min, P = 0.03).Conclusions:
These results suggest that, in hyperthyroidism, insulin-stimulated glucose uptake in muscle is impaired; this defect is corrected, at least in part, by the increases in BF.