1. Actions of Captopril, Enalapril, Lisinopril, and Other ACE Inhibitors
As outlined earlier, during heart failure the body tries to maintain blood pressure at all costs in order to satisfy the needs of the brain and organs. If the blood pressure falls or the volume of blood reaching the kidneys falls, as occurs during bleeding or heart failure, the renin-angiotensin enzyme system is activated and angiotensin is produced. Angiotensin is a powerful constrictor of arteries and increases blood pressure, but this increases the work of the heart and worsens heart failure. Captopril and enalapril block a ‘‘converting enzyme’’ that converts angiotensin to its active component. This new group of vasodilators are therefore called angiotensin-converting enzyme (ACE) inhibitors. These drugs cause dilatation of the arteries, which reduces blood pressure and heart work. In addition, these drugs cause the kidneys to return less sodium and water to the blood, further reducing the work of the heart. ACE inhibitors conserve potassium, and as mentioned, a normal potassium level is essential for the prevention of digitalis toxicity and the maintenance of the electrical stability of the heart. Available ACE inhibitors include captopril, enalapril, and lisinopril. (See chapter entitled Angiotensin-Converting Enzyme Inhibitors/Angiotensin Receptor Blockers.)

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