Hyperinsulinemia, insulin resistance and essential hypertension.

Glucose intolerance and noninsulin-dependent diabetes are commonly associated with hypertension. Epidemiological data suggest that this association is independent of age and obesity. Much evidence indicates that the link between diabetes and essential hypertension is hyperinsulinemia. When hypertensive patients whether obese or of normal weight are compared with matched normotensive control subjects, an increased plasma insulin response to a glucose challenge is consistently observed. Studies using insulin glucose clamp techniques in combination with tracer glucose infusion and indirect calorimetry have demonstrated that the insulin resistance in hypertensive subjects is located in muscles and restricted to glycogen synthesis. The relations between hyperinsulinemia and blood pressure do not prove that the relationship is a causal one. However, at least four mechanisms may link hyperinsulinemia with hypertension: Na+ retention, sympathetic nervous system overactivity, disturbed membrane ion transport and proliferation of vascular smooth muscle cells. Diuretics and beta-blockers may enhance insulin resistance, which is not affected by calcium antagonists, but decreased by the ACE inhibitor captopril. Weight reduction and regular physical exercise can improve insulin sensitivity and decrease blood pressure values. These nonpharmacological interventions should be more strongly recommended to diabetic and nondiabetic hypertensive patients.