Glucose transporter 2 concentrations in hyper- and hypothyroid rat livers

The deterioration of glucose metabolism frequently observed in hyperthyroid ism may be due in part to increased gluconeogenesis in the liver and glucos e efflux through hepatocyte plasma membranes. Glucose transporter 2 (GLUT 2 ), a facilitative glucose transporter localized to the liver and pancreas, may play a role in this distorted glucose metabolism. We examined changes in the levels of GLUT 2 in livers from rats with L-thyr oxine-induced hyperthyroidism or methimazole-induced hypothyroidism by usin g Western blotting to detect GLUT 2. An oral glucose tolerance test revealed an oxyhyperglycemic curve (impaired glucose tolerance) in hyperthyroid rats (n=7) and a flattened curve in hyp othyroid rats (n=7). GLUT 2 levels in hepatocyte plasma membranes were sign ificantly increased in hyperthyroid rats and were not decreased in hypothyr oid rats compared with euthyroid rats. The same results were obtained with a densitometric assay. These findings suggest that changes in the liver GLU T 2 concentration may contribute to abnormal glucose metabolism in thyroid disorders.