INSULIN-RESISTANCE AND HYPERTENSION

Insulin resistance and reactive hyperinsulinemia occur not only in patients with obesity, impaired glucose tolerance or non-insulin-dependent (Type 2) diabetes mellitus, but also in many non-obese, non-diabetic individuals with essentiell hypertension and their normotensive, lean young offsprings. The common coexistance of a genetic predisposition for hypertension with insulin resistance helps to explain the frequent occurrence of hypertension as well as dyslipidemia, obesity and diabetes Type 2 in a given individual. In the pathogenesis of hypertension, inappropriate vasoconstriction and/or a structural vasculopathy appears to be an important and ultimate causative event. Several presser mechanisms are discussed and a distinct sodium retention appears to be almost obligatory associated with diabetes mellitus, while essential and particularly obesity-associated hypertension involves predominantly a tendency for sympathetic activation. Acute hyperinsulinemia on one hand causes arterial vasodilation and on the other hand enhances renal sodium reabsorbtion and sympathetic activity. Chronically, hyperinsulinemia may promote cardiovascular muscle cell proliferation and atherogenesis. Insulin resistance affecting certain transmembrane cation transporters might lead to an elevation of intracellular cytosolic calcium levels thereby inducing inappropriate vasoconstriction. Nevertheless, whether insulin resistance and hyperinsulinemia contribute to the pathogenesis of hypertension per se is still unproven. Considering antihypertensive drugs, thiazide diuretics given in medium or high dosage as well as beta-blockers appear to promote insulin resistance, reactive hyperinsulinemia and dyslipidemia. Almost all calcium antagonists and the conventional sympthatolytics are metabolically neutral, while ACE-inhibitors and alpha(1)-blockers tend to improve insulin resistance. In Type 2 diabetic patients, ACE-inhibitors exert in addition to their antihypertensive a potentially useful antidiabetic effect, Nevertheless, the prognostic relevance of the metabolic side effects of antihypertensive drugs awaits further clarification.