Hemodynamic and counterregulatory effects of calcium antagonists in hypertension.

Increased systemic vascular resistance in essential hypertension depends on increased calcium influx. Calcium antagonists lower cytosolic free calcium concentrations mainly through a reduction of transmembraneous calcium influx and are potent arterial vasodilators. Dihydropyridine calcium antagonists are pharmacologically more potent with respect to arterial vasodilatation than verapamil- or diltiazem-type calcium antagonists and have less or no clinically detectable negative inotropic effects, but this seems to be of importance only in patients with reduced cardiac function. All calcium antagonists lower high blood pressure through a reduction of elevated systemic vascular resistance without clinically relevant activation of sympathetic reflexes or the renin-angiotensin-aldosteron system. However, subtle changes of sympathetic nervous system activity may codetermine the acute and chronic blood pressure response. They do not lead to volume retention because of improved intrarenal hemodynamics and a diuretic effect. Interference with angiotensin and sympathetically mediated vasoconstrictor mechanisms probably also contributes to their antihypertensive effect. This hemodynamic profile is similar for all calcium antagonists but the degree of acute sympathetic stimulation seems to be greater for dihydropyridines. Their overall favorable hemodynamic and neurohumoral profile and their proven efficacy and lack of serious side effects have made calcium antagonists a valuable addition to the armanentarium available for monotherapy of hypertension.