Adrenoreceptor-mediated effect of neuropeptide Y decreases cardiac inotropic responses

Abstract

The effect of neuropeptide Y on the number and affinity of catecholamine receptors in the ventricular myocardium was investigated. Receptor binding studies showed that incubation of cardiac membrane in the presence of neuropeptide Y (NPY, 10 −7 M) decreased the number of α/β-adrenoceptor binding sites ( B max) without affecting the affinity ( K D) of these receptors. Although not able to modulate the contractility by itself, NPY was able to decrease the positive inotropic effects of phenylephrine and isoproterenol in the isolated, perfused myocardium. Ca 2+ Mg 2+- ATPase activity, measured from the sarcolemma, sarcoplasmic reticulum and myofibrils, was unaltered whereas the activity of sarcolemmal Na + K +- ATPase was decreased when NPY was included in the media. On the other hand, NPY was shown to increase the phosphoinositide-phospholipase C associated with the sarcolemma. These findings support the hypothesis that NPY modulates postsynaptic adrenergic receptors in the myocardium and can affect the adrenergic-induced, inotropic response.