Neural reflexes of cardiac origin manifested during myocardial ischemia and reperfusion can lead to hemodynamic alterations, arrhythmias, nausea, vomiting and angina. Reactive oxygen species are thought to play an important role in local tissue injury during ischemia and reperfusion. Nicotine may attract neutrophils, a source of reactive oxygen species, to the myocardium. The hypothesis of this proposal is that during myocardial ischemia free radicals are produced, their concentrations are enhanced by the presence of nicotine and that H2O2, and species derived from H2O2, particularly .OH, are capable of activating sympathetic and vagal afferents from the myocardium to reflexly alter heart rate, myocardial contractility and peripheral vascular resistance. Initially we will measure directly the production of .OH during ischemia and reperfusion using phenylalanine to trap.OH in the myocardium before and during infusion of nicotine. Secondly, H2O2 will be applied to the epicardial surface of the anterior or inferoposterior regions of myocardium to develop a dose-response curve (i.e., an H2O2 vs cardiovascular response relationship). The response to H2O2 will be determined before and after vagotomy and/or stellectomy. The importance of free reactive oxygen species will be examined using the scavenger, dimethylthiourea (DMTU), while the role of .OH will be studies with deferoxamine (DEF) to chelate iron and to inhibit the Haber Weiss reaction. Thirdly, single unit cardiac sympathetic afferent activity will be recorded to evaluate the types of afferent nerves stimulated during regional myocardial ischemia/reperfusion in the presence and absence of nicotine, and to document the role of reactive oxygen species, using DMTU, and .OH, using DEF, which may be involved in the activation of the afferent nerve endings. The role of other chemical metabolites, including lipoxygenase and cyclooxygenase products, adenosine and bradykinin, as mediators of the response to reactive oxygen species will be studies by employing selective receptor antagonists. We expect that our studies will demonstrate a central role for reactive oxygen species in activating sympathetic afferent nerve endings during anterior ischemia whereas vagal afferent endings will be preferentially stimulated by these species during inferior myocardial ischemia. Furthermore, we will document reflex activation of the cardiovascular system. Nicotine will increase the production of reactive oxygen species in ischemic and particularly in reperfused myocardium. Metabolites, such as arachiadonic acid products, adenosine or kinins, will not be required for the reactive oxygen species- induced stimulation of cardiac afferents during ischemia/reperfusion. Such information will provide clinicians with a better understanding of potentially dangerous cardiac reflexes and may suggest therapeutic approaches designed to limit these untoward events.
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