Nitrates and angina pectoris.

This review discusses the mechanisms of action of the organic nitrates, nitrate tolerance, and the effects of nitrates in patients with stable angina pectoris. The nitrates are prodrugs that enter the vascular smooth muscle, where they are denitrated to form the active agent nitric oxide (NO). NO activates guanylate cyclase, which results in cyclic guanosine monophosphate (cGMP) production and vasodilation as a result of reuptake of calcium by the sarcoplasmic reticulum. NO is identical to endothelium-derived relaxing factor (EDRF), which induces vasodilation, inhibits platelet aggregation, reduces endothelium adhesion, and has anticoagulant and fibrinolytic effects. Thus, the nitrates may be more than vasodilators and, in addition to reducing ischemia, may affect the process of atherosclerosis. The vascular effects of nitrates are attenuated during sustained therapy. Although the basis for the phenomenon of nitrate tolerance is not completely understood, sulfhydryl depletion as well as neurohormonal activation and increased plasma volume may be involved. The administration of N-acetylcysteine, angiotensin-converting enzyme (ACE) inhibitors, or diuretics do not consistently prevent nitrate tolerance. At present, intermittent nitrate therapy is the only way to avoid nitrate tolerance. The intermittent administration of nitrates, however, cannot provide continuous therapeutic benefits, and thus monotherapy with nitrates is not suitable for many patients with stable angina pectoris.