Glycogen synthase activity in two rat models of hypertension

Several studies on both humans and animal models have reported a pathogenetic relationship among hyperinsulinism, insulin resistance, and hypertension. We have previously evaluated whole body glucose disposal and insulin sensitivity in different models of hypertensive rats, showing an increase rather than an impairment of glucose metabolism, which in turn was due to an improved ability of insulin to channel the absorbed glucose towards the nonoxidative disposal. Aiming to confirm our previous findings we performed the direct assay of skeletal muscle glycogen synthase on tissue samples from the previous clamp studies, as a rate limiting step enzyme of glycogen synthesis, under conditions of physiologic hyperinsulinemia and euglycemia. Glycogen synthase was assayed on samples from rectus muscle tissues of spontaneously hypertensive rats and high sodium, one kidney, one figure-8 hypertensive rats. Compared to controls, our data show an increased activity of glycogen synthase in the hypertensive animals, which is consistent with the increased glycogen synthesis previously reported. In conclusion, under our experimental conditions, hypertension and chronic hyperadrenergism are associated with an increased ability of insulin to stimulate glucose uptake and disposal. These latter effects are mainly due to an increase in nonoxidative disposal and glycogen synthase activity.