TRANSMURAL REGULATION OF MYOCARDIAL PERFUSION BY NEUROPEPTIDE-Y

In vivo studies have shown that sympathetic nerve stimulation improves the transmural distribution of myocardial perfusion by increasing the endocardial/epicardial flow ratio; however, the mechanism of this eff ect is unknown. During nerve stimulation both norepinephrine (NE) and neuropeptide Y (NPY) are released, either or both of which may exert v asoconstrictor effects. The present studies were performed to examine the effects of these two cotransmitters on the transmural distribution of myocardial perfusion in a canine model. In anesthetized open-chest dogs, during maximal coronary vasodilation with intracoronary adenosi ne, both neuropeptide Y (29.7 mu g/min) and norepinephrine (0.5 - 2.0 mu g/min) reduced myocardial perfusion to a greater extent in the epic ardium than in the subendocardium. The endo/epi ratio with adenosine a lone was 1.11 +/- 0.02. Norepinephrine increased this by 80 %, neurope ptide Y by 20 %, and the combination of the two by 76 % (P < 0.05 for all three vs. adenosine). Neuropeptide Y alone constricted the coronar y vasculature but did not alter transmural flow. Thus neuropeptide Y p referentially reduces myocardial perfusion in the epicardium. We specu late that neuronally released neuropeptide Y contributes importantly t o the transmural distribution of myocardial perfusion during sympathet ic nerve stimulation.