The endothelium in coronary artery disease

An increasing body of evidence indicates that the endothelium is crucially involved in the regulation of coronary blood flow and cardiac function. Injury to the endothelium precipitates atherosclerosis by leading to smooth-muscle-cell migration and proliferation, induction of expression of growth factors and impairment in the plasmatic coagulation and endogenous fibrinolysis system. Strategically located between the circulating blood and the vascular smooth muscle, endothelial cells release numerous vasoactive substances regulating the function of vascular smooth muscle and trafficking blood cells. Important endothelium-derived vasodilators are prostacyclin, bradykinin, nitric oxide and, independent of the former, endothelium-derived hyperpolarizing factor. In particular, nitric oxide inhibits cellular growth and migration. In concert with prostacyclin, nitric oxide exerts potent antiatherogenic and thromboresistant properties by preventing platelet aggregation and cell adhesion. These effects are counterbalanced by endothelial vasoconstrictors, such as angiotensin II and endothelin-1, both of which exert prothrombotic and growth-promoting properties. Modern therapeutic strategies in coronary artery disease focus on preserving or restoring endothelial integrity. Whereas nitrates partly substitute deficient endogenous nitric oxide, calcium antagonists counteract angiotensin II and endothelin-l at the level of vascular smooth muscle by reducing Ca2+ inflow and facilitating the vasodilator effects of nitric oxide. Beyond inhibiting the renin-angiotensin system, angiotensin-converting enzyme inhibitors diminish the inactivation of bradykinin, thus leading to an augmentation of nitric oxide release. Furthermore, newly developed specific endothelin antagonists will provide us with greater insight into the beneficial effects of restoring endothelial dysfunction in cardiovascular disease. Thus, drugs can directly affect endothelial function, prevent the action of endothelial mediators, substitute for deficient endothelial factors or indirectly exert protective effects by interfering with cardiovascular risk factors.