Effect of hyperglycemia on serum T4 and T3 levels in rats

In order to elucidate the effect of hyperglycemia on serum thyroid hormone levels, serum T4 and T3 concentrations were measured in rats with continuous intravenous glucose infusion. 30% glucose solution was infused into the left jugular vein at a rate of 1 ml/hr for 12 hr, and serum glucose level was maintained at 400 mg/dl. Serum T4 levels were slightly but not significantly decreased and serum T3 levels were significantly decreased by infusion of glucose for 12 hr. The ratio of serum T3 to T4 was not significantly changed in rats with glucose infusion. These results suggest an inhibitory effect of hyperglycemia on thyroid hormone release.