In vivo insulin action and muscle glycogen synthase activity in Type 2 (non-insulin-dependent) diabetes mellitus: effects of diet treatment

Abstract

Insulin resistant glucose metabolism is a key element in the pathogenesis of Type 2 (non-insulin-dependent) diabetes mellitus. Insulin resistance may be of both primary (genetic) and secondary (metabolic) origin. Before and after diet-induced improvement of glycaemic control seven obese patients with newly-diagnosed Type 2 diabetes were studied with the euglycaemic clamp technique in combination with indirect calorimetry and forearm glucose balance. Muscle biopsies were obtained in the basal state and again after 3 h of hyperinsulinaemia (200 mU/l) for studies of insulin receptor and glycogen synthase activities. Similar studies were performed in seven matched control subjects. Insulin-stimulated glucose utilization improved from 110±11 to 183±23 mg·m-2·min-1 (p<0.03); control subjects: 219+23 mg·m-2·min-1 (p=NS, vs post-diet Type 2 diabetes). Nonoxidative glucose disposal increased from 74±17 to 138+19 mg·m-2·min-1 (p<0.03), control subjects: 159±22 mg· m-2·m-1 (p=NS, vs post-diet Type 2 diabetic patients). Forearm blood glucose uptake during hyperinsulinaemia increased from 1.58±0.54 to 3.35±0.23 μmol·l-1·min-1 (p<0.05), control subjects: 2.99±0.86 μmol·l-1·min-1 (p=NS, vs post-diet Type 2 diabetes). After diet therapy the increase in insulin sensitivity correlated with reductions in fasting plasma glucose levels (r=0.97, p<0.001), reductions in serum fructosamine (r=0.77, p<0.05), and weight loss (r=0.78, p<0.05). Values of muscle glycogen synthase sensitivity to glucose 6-phosphate (A0.5 for glucose 6-phosphate) were similar in the basal state. However, insulin stimulation of glycogen synthase was more pronounced after diet treatment (A0.5: 0.43±0.06 (before) vs 0.30±0.04 mmol/l (after); p<0.03; control subjects: 0.22±0.03 mmol/l). Muscle insulin receptor binding and kinase activity were similar before and after diet treatment and comparable to values in the control group. The data suggest that impaired insulin stimulation of in vivo glucose turn-over and muscle glycogen synthase activity tend to be restored during successful diet treatment of patients with Type 2 diabetes. © 1992 Springer-Verlag.