Two forms of vasoconstriction in systemic hypertension

Abstract

Clinical, pharmacologic and biochemical evidence characterizes essential hypertension as a heterogeneous spectrum of pathophysiologic substances rather than the single entity it has long been presumed to be. Although the causes of essential hypertension remain obscure, 2 different mechanisms for long-term vasoconstriction that sustain diastolic hypertension in the experimental and clinical forms of primary aldosteronism and renovascular hypertension can also be identified and quantified among patients with essential hypertension. The first mechanism is renin independent, requires antecedent sodium retention and appears related to abnormal membrane transport of calcium. This vasoconstriction is identified by low plasma renin and ionized calcium and is correctable by sodium depletion or calcium channel or α blockade. The second vasoconstrictor mechanism is renin mediated and involves an increase in cytosolic calcium. This mechanism is quantifiable by the plasma renin level or the hypotensive response to an antirenin-system drug (converting enzyme inhibitor, β blocker or saralasin). Depending on the state of sodium balance, these 2 mechanisms contribute reciprocally to maintenance of arteriolar tone in experimental models, in both normal and hypertensive people, and in patients with congestive heart failure. In these situations, at the extremes of the range of plasma renin values, one or the other mechanism predominates, whereas in the medium range of renin values both mechanisms can be operative. These interrelations provide a basis for applying more precisely tailored therapy and for stratifying patients pathophysiologically for further study.