The effect of in vivo thyroxine treatment on insulin receptors, glucose transport and GLUT4 in rat adipocytes.

Daily i.p. administration of thyroxine (T4; 50 micrograms/100 g BW) to adult male rats for one week doubled the thyroxinemia and induced significant augmentation of glycemia and insulinemia. Hyperthyroxinemia was also manifested by significant elevation of liver malic enzyme activity and by the presence of smaller fat cells. Adipocytes of T4 treated rats displayed significantly lower density of insulin receptors, decreased insulin stimulatory effect on glucose transport and less glucose transporter (GLUT4) protein in plasma membranes after insulin stimulation as those of controls. These results indicate a deleterious effect of hyperthyroxinemia on insulin controlled glucose metabolism in fat cells.