INSULIN SENSITIVITY IN HYPERTHYROIDISM: MEASUREMENT BY THE GLUCOSE CLAMP TECHNIQUE

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Abstract
SUMMARY: Sensitivity to porcine insulin has been compared in overnight fasted hyper‐ thyroid and control subjects using a euglycaemic clamp technique. Basal values for blood glucose, lactate, pyruvate, alanine, serum insulin and C‐peptide were similar in the two groups, whilst blood glycerol (hyperthyroid 0.11 ± 0.02 (mean ± S.E.) vs. control 0.06 ± 0.01 mmol/l,P< 0.01) and blood 3‐hydroxybutyrate (0.28 [0.03–0.79, range] vs 0.09 [0.01–0.29] mmol/l,P< 0.05) were increased in hyperthyroidism. During the 2 hour insulin infusion (0.05 U/kg/h), serum insulin plateaued at the same level (44 ± 4 vs 44 ± 1 mU/l) and insulin metabolic clearance rates were similar (1.21 ± 0.10 vs 1.25 ± 0.03 l/min). Serum C‐peptide levels also decreased by similar amounts (40 ± 8 vs 47 ± 6%). The amount of glucose infused to maintain euglycaemia was identical during the second hour of insulin infusion (290 ± 50 vs 330 ± 30 mg/kg) as were the increments in lactate and pyruvate concentrations. Blood glycerol values decreased in both groups although values in hyperthyroid patients remained significantly higher than in controls. 3‐Hydroxybutyrate concentrations fell to similar values in the two groups. These findings suggest that insulin‐stimulated glucose metabolism and inhibition of ketogenesis are normal in hyperthyroidism.