The hypotheses that vasoactive intestinal peptide (VIP) is evenly distributed throughout atrial and ventricular myocardium and is present in postganglionic parasympathetic neurons in the regions of the sinoatrial and atrioventricular nodes were tested in three groups of dogs. Neuropeptide Y (NPY) tissue concentrations were determined in each group. In six sham dogs VIP and NPY concentrations were evenly distributed and were higher in atria compared with ventricles. In nine parasympathectomized dogs, VIP concentrations in sample sites from regions of the sinoatrial and atrioventricular nodes were comparable to those in sham-operated controls. In nine denervated dogs VIP concentrations were significantly decreased in three adjacent sample sites along the atrioventricular groove. In these dogs NPY concentrations were not detectable or were significantly decreased at all sample sites of both atria and ventricles. These data suggest that VIP neurons are evenly distributed in atrial and ventricular myocardium but do not originate in parasympathetic ganglia supplying the sinoatrial and atrioventricular nodes. The data also demonstrate the possible presence of extrinsic VIP neurons in the canine right ventricle and indicate that NPY may be a useful marker of myocardial adrenergic innervation.
Target specificity of neuropeptide Y-immunoreactive cranial parasympathetic neurons
