Mechanism of action of calcium antagonists in heart and vascular smooth muscle.

Abstract

A transmembrane supply of Ca2+ ions is required for active tension development in both vascular smooth musculature and myocardial fibres. Ca2+ antagonists thus not only damp hyperkinetic myocardial dysfunction but also act against practically all vasoconstrictor or spastic responses of extramural coronary smooth muscle. Clinically important targets of Ca2+ antagonists include the pulmonary, cerebral, mesenteric and renal arteries, as well as the peripheral resistance vessels of the systemic circulation. Ca2+ antagonists are used increasingly to treat acute hypertensive crises as well as for long-term antihypertensive therapy. In physiological experiments, Ca2+ antagonists not only neutralize various vasoconstrictor agents but also greatly reduce the sensitivity of the systemic arteries and arterioles to mechanical stimuli such as extension of the vascular wall by a rise in intraluminal pressure. In human arterial walls, at an advanced age, cytotoxic degrees of Ca2+ overload probably play an important role in the pathogenesis of arteriosclerotic lesions. Severe diabetics and heavy smokers exhibit an even faster progression of age-dependent arterial calcinosis. In rats, the Ca2+ antagonist verapamil not only prevented arterial calcinosis due to overdoses of vitamin D and dihydrotachysterol but also counteracted age-dependent Ca2+ accumulation. Spontaneously hypertensive rats also exhibit progressive arterial Ca2+ overload which responds excellently to the Ca2+ antagonists nifedipine, nimodipine, nisoldipine, nitrendipine, as well as to verapamil and diltiazem. Suitable Ca2+ antagonists could possibly retard or even prevent premature arterial calcinosis in humans. Moreover, Ca2+ antagonists exert a direct cardioprotective effect on the myocardium by preventing intracellular Ca2+ overload.