In vivo glucose turnover in hypo- and hyperthyroid starved rat

The effect of hypo- and hyperthyroidism on glucose turnover in vivo was determined in unanesthetized rats starved for 48 h. Glucose pool and decay rate of specific radioactivity of blood glucose was measured after bolus injection of a mixture of 3H-(2)- and 14C-(U)-glucose under steady state conditions. Compared with euthyroid controls (= 100%), hypothyroidism resulted in a decrease of blood glucose concentration (81%), glucose pool (52%), glucose disappearance rate (39%), and total glucose recycling (12%). In contrast, hyperthyroidism led to an increase of blood glucose concentration (148%), glucose pool (121%), glucose disappearance rate (185%), and total glucose recycling (163%). T 1/2 for glucose was calculated to be 46 min in the hypo-, 34 min in the eu-, and 22 min in the hyperthyroid state. The concentration of circulating glucoregulatory hormones, corticosterone and glucagon were elevated in hyperthyroid rats, while glucagon was diminished in hypothyroid animals. No difference in the level of insulin was found. These data demonstrate that glucose turnover in vivo is a function of the thyroid state being reduced in hypo- and considerably increased in hyperthyroidism.