The mechanisms of hypertension and the role of ACE inhibitors.

Hypertension, a condition characterized by narrowing of the arteriolar lumen, is related in part to vasoconstriction and in part to vascular hypertrophy. Complex and interlocking mechanisms involving the autonomic nervous system and both circulating and local vasoconstrictor and vasodilator hormones contribute to this narrowing. Endothelin, 5-HT (serotonin), the kinins and ouabain may all participate by altering sodium, potassium and calcium fluxes in vascular smooth muscle cells. Recently the concept of insulin resistance as a mechanism of hypertension has emerged. Insulin may be a vascular growth factor as well as a local hormone facilitating a rise in intracellular sodium concentration. The observation that ACE inhibitors lower BP when plasma renin and angiotensin levels are low has led to an increased interest in local non-circulating renin-angiotensin systems. These systems probably influence arteriolar tone as well as vascular hypertrophy, and their inhibition leads to reduction in BP and some reversal of arteriolar thickening. Thus the ACE inhibitors represent a logical and effective method of treating hypertension and their use is likely to increase in the next few years.