Effect of insulin on renal sodium handling and renal haemodynamics in insulin-dependent (type 1) diabetes mellitus patients

The effects of insulin on renal haemodynamics and renal sodium handling were studied in eight insulin-dependent (type 1) diabetic patients (aged 30+/-3 years). Seven healthy men (aged 38+/-4 years) served as controls. The type 1 diabetic patients were resistant to insulin-stimulated glucose disposal as estimated by a 45% lower metabolic (P<0.01) clearance of glucose as compared with controls. However, type 1 diabetic patients were still sensitive to the distal tubular antinatriuretic effect of insulin, as indicated by an increase in distal sodium reabsorption (95.5%+/-0.5% to 96.9%+/-0.4%; P<0.05) during insulin infusion compared with controls (95.5%+/-0.6% to 97.4%+/-0.3%; P<0.05). In control subjects insulin infusion was associated with 9% increases (P<0.05) in lithium clearance and in renal plasma flow, whereas no significant increases in lithium clearance and in renal plasma flow were observed in the type 1 diabetic patients. In both groups, the changes in renal plasma flow in response to insulin infusion were positively correlated with that in lithium clearance (r=0.80 and r=0.90, respectively; P<0.05-0.01). In conclusion, the present result demonstrates an intact distal tubular sodium retaining effect in conjunction with a blunted decrease in proximal tubular sodium reabsorption following insulin infusion, which could be the result of an impaired renal vasodilation in type 1 diabetes mellitus.