Thiol-containing agents in the management of unstable angina pectoris and acute myocardial infarction.

The development of unstable angina pectoris and acute myocardial infarction is a process of platelet aggregation and thrombus formation associated with local coronary vasoconstriction. Regional deficiencies in endothelial vasodilator function, due to reduced formation of endothelium-derived relaxing factor (EDRF), may predispose to platelet aggregation and coronary vasoconstriction. Nitroglycerin (NTG), frequently utilized in the management of unstable angina pectoris and acute myocardial infarction, undergoes bioconversion, via a sulfhydryl-dependent process, to nitric oxide, which is identical or closely related to EDRF. Other products of the nitrate bioconversion "cascade" are various S-nitrosothiols, which, like nitric oxide, activate soluble guanylate cyclase, inducing increased formation of cyclic guanosine monophosphate. NTG potentially may act to correct a localized deficiency of EDRF effect, at both the vasculature and platelet levels. In patients with unstable angina, hemodynamic effects and therapeutic efficacy of intravenously infused NTG may be attenuated within hours. Combined therapy with NTG and intravenously infused N-acetylcysteine (NAC) results in potentiation of hemodynamic responses to NTG, markedly augments the effects of NTG on platelet aggregation, and reduces the incidence of acute myocardial infarction in patients with severe unstable angina pectoris. The combination of NTG with intermittent NAC infusion may increase the risk of hypotensive episodes in such patients, whereas continuous coinfusion of the drugs is better tolerated. The combination of NTG with thiol-containing agents, such as NAC, may be of therapeutic value in unstable angina pectoris and in evolving acute myocardial infarction. This is currently under investigation.