Insulin resistance, hyperinsulinemia and hypertension.

Association between insulin resistance and hypertension: Insulin resistance and reactive hyperinsulinemia occur not only with obesity, impaired glucose tolerance or non-insulin-dependent (type 2) diabetes mellitus, but also in many non-obese, non-diabetic patients with essential hypertension and their currently normotensive, lean young offspring and in some other conditions known to promote hypertension. Insulin resistance impairs glucose tolerance, while insulin resistance and/or hyperinsulinemia promote dyslipidemia, body fat deposition and probably atherogenesis. Therefore, the common coexistence of a genetic predisposition for hypertension with insulin resistance helps to explain the frequent, although temporally often dissociated, occurrence of hypertension as well as dyslipidemia, obesity and type 2 diabetes in a given subject. Pathogenetic mechanisms: In the pathogenesis of hypertension, inappropriate vasoconstriction (due to dysbalance of vasoactive substances and/or raised cytosolic Ca2+) and/or a structural vasculopathy is a very important ultimate causative event. In the presumed mosaic of participating pressor mechanisms, distinct Na+ retention is almost obligatory with diabetes mellitus, while essential and particularly obesity-associated hypertension probably involves a tendency for sympathetic activation. Development of insulin resistance: Insulin resistance may develop as a consequence of an intracellular excess of Ca2+ or decrease in Mg2+, an impaired insulin-mediated rise in skeletal muscle blood flow, increased sympathetic activity or being overweight. Acute hyperinsulinemia on the one hand causes arterial vasodilation and on the other hand enhances renal sodium reabsorption and sympathetic activity. Chronically, hyperinsulinemia may promote cardiovascular muscle cell proliferation and atherogenesis, and it has been proposed that insulin resistance in certain transmembranous cation exchange systems may elevate cytosolic Ca2+. Nevertheless, whether insulin resistance and/or hyperinsulinemia itself contribute to the pathogenesis of hypertension is still unclear.