Atriopeptin distribution in the developing rat heart

The embryonic distribution of atriopeptin (atrial natriuretic factor) in the Sprague-Dawley rat heart was mapped by immunoperoxidase staining of embryonic and neonatal hearts using rabbit antiserum to atriopeptigen purified from adult rat atrium. During the period of cardiac septation (days 14 and 16), immune serum reacted strongly with myocardial cytoplasmic granules in two sites: the inner cell layer along the cephalic curvature of the atria and the trabeculae of the incompletely divided ventricles. The youngest hearts studied (gestational day 11) displayed only nonspecific diffuse peroxidase reactivity within blood cells, indistinguishable from control sections incubated with normal rabbit serum. One week following birth, intense anti-atriopeptin reactivity was widely distributed through both atria. In addition, immunoreactive cytoplasmic granules were found at several sites in the ventricular myocardium. Along the fiber tracts of the concentric layers of the ventricular walls and interventricular septum, scattered granular foci were seen between nuclei of contiguous elongated myocytes. Positive staining was also seen within the papillary muscles and trabeculae carnae, regions shown by Alcian blue/periodic acid-Schiff base staining of sister sections to be relatively rich in glycogen. These patterns of antibody reactivity suggest the coupling of early atriopeptin secretory activity with developing cardiac function.