Immunohistochemical localization of cardiodilatin in myoendocrine cells of the cardiac atria.

Region-specific antibodies against synthetic N-terminal fragments of cardiodilatin (CDD) were raised in rabbits and used for the immunohistochemical detection of this new peptide hormone in the myoendocrine cells within the cardiac atria of several species. The peroxidase-antiperoxidase (PAP) and fluorescein isothiocyanate (FITC) immunohistochemical methods gave identical results of cardiodilatin-immunoreactivity (CDD-IR) within the tissue. In addition to the porcine right atrial appendage, myoendocrine cells with CDD-IR were also detected in the left atrium of porcine heart, as well as in other species such as dog and cat. The exact localization of the immunoreactivity in specific secretory granules was mostly related to the Golgi-area which is located on both nuclear poles of auricular myoendocrine cells. The results confirm that cardiodilatin is stored in secretory granules observed through electron microscopical means. This hormone is most likely synthesized and released in myoendocrine cells, exerting its important cardiovascular effects.