Desensitization by neuropeptide Y of effects of sympathetic stimulation on cardiac vagal action in anaesthetised dogs

Abstract The effects of a long-lasting intravenous infusion of neuropeptide Y (NPY, 180 ± 8 min, 53 ± 4 μ g/kg/h) on the prolonged inhibition of cardiac vagal action evoked by cardiac sympathetic nerve stimulation and bolus intravenous injections of NPY were investigated in anaesthetised dogs. Sympathetic stimulation and NPY injection were performed on four separate occasions: once in control conditions, then once early and again late in the period of NPY infusion, and then on a final occasion 60–90 min after the cessation of NPY infusion. The maximum inhibition of cardiac vagal action evoked by an injection of NPY was significantly less late in the NPY infusion when compared with the other three injection groups (ANOVA, P P P P