Experimental basis of the long-term therapy of arterial hypertension with calcium antagonists

In vascular smooth muscle (as in myocardial fibers) a transmembrane supply of Ca++ ions is required for active tension development. In consequence, Ca++ antagonists, which restrict transmembrane Ca++ delivery, possess a wide scope of action against practically all types of vasoconstrictor or spastic reactions on coronary, pulmonary, cerebral, renal or mesenteric arteries. Another important target of Ca++ antagonists is the resistance vessels of systemic circulation in both animals and humans. Thus, Ca++ antagonists are successfully used for the treatment of acute hypertensive crises as well as for long-term antihypertensive therapy. Spontaneously hypertensive rats (SHRs) also respond to suitable Ca++ antagonists with a dramatic fall in blood pressure. The acute spasmolytic effects of Ca++ antagonists can be directly visualized by ophthalmoscopic examination of the arterioles in the ocular fundus. In untreated SHRs these arterioles are always heavily constricted, and aneurysm-like luminal protuberances develop. In contrast, after 1 adequate Ca++ antagonist dose, blood pressure instantaneously falls to its normal level while the retinal arterioles dilate. A further important effect of Ca++ antagonists that we have demonstrated in experiments on SHRs is the prevention of progressive arterial Ca++ overload, which otherwise produces severe calcinotic or arteriosclerotic damage of the arterial walls. However, with the help of Ca++ antagonists, arterial integrity can be totally preserved. Interestingly, this anticalcinotic arterial protection by Ca++ antagonists may also manifest itself independent of any blood pressure change. This is true of arterial calcinosis in normotensive rats because of advanced age, alloxan diabetes or intoxication with overdoses of vitamin D3, dihydrotachysterol or nicotine.