Abstract
The cardiac hormone atrial natriuretic peptide (ANP) is known to be produced by the atrial myocardiocytes. In the ventricles, the concentrations of ANP are very low and are often undetectable by immunocytochemistry. Apart from recent reports of ANP in the various Purkinje cell types, the histological distribution of the small amounts of ANP in the ventricular myocardium has not been well established. In this study, the distribution of ANP immunoreactivity in the ventricles of normotensive adult rats was examined with a modified version of an immunostaining procedure. ANP immunoreactivity was present, in addition to typical myocardial cells, in the myocardiocytes surrounding the arteries and arterioles, particularly at their bifurcations. The specificity of the immunostaining was confirmed with pre-absorption controls. Such a distribution indicates that in addition to being an endocrine hormone ANP may have a paracrine function. The periarterial myocardiocytes may be able to sense the pressure and/or volume changes of the surrounded blood vessels and to release ANP, which may in turn affect these blood vessels and thereby regulate coronary perfusion. The physiological and pathological significance of periarterial ANP distribution warrants further investigation.