Abstract :
Angiotensin-converting enzyme (ACE) inhibitors have shown unexpected benefits in the prevention of ischemic events in patients with hypertension and congestive heart failure. In addition to these clinical observations, there is a growing body of knowledge about the molecular and cellular effects of ACE inhibitors. For example, ACE inhibition prevents stimulation of smooth muscle cell angiotensin II receptors, thereby blocking both contractile and proliferative actions. Angiotensin II blockade also diminishes the production of superoxide anion, which inactivates ambient nitric oxide. ACE inhibition of kininase II inhibits the breakdown of bradykinin, a direct stimulant of nitric oxide release from the intact endothelial cell. Thus, at the cellular level within the vasculature, ACE inhibition shifts the balance of ongoing mechanisms in favor of those promoting vasodilatory, antiaggregatory, antithrombotic, and antiproliferative effects. These effects underlie the potential benefits of ACE inhibition in the therapy of ischemia and atherosclerosis. Some data is available in humans to show that these effects can be sustained for months, thereby maintaining improved endothelial function and, presumably, allowing the initiation of steps that might alter the progression of atherosclerosis. Definitive information is not yet available in humans to show that ACE inhibition clearly alters the progression of atherosclerosis or diminishes coronary events in uncomplicated coronary disease. This promising area of investigation is, however, the subject of multiple clinical trials, which should provide clarification of this important question in coming years.
