The hearts of different mammalian and submammalian species that have so far been examined all appear to be the source of a novel peptide hormone, variously termed atrial natriuretic peptide (ANP), cardiodilatin (CDD) and/or cardionatrin. Despite the well-established role of ANP as an important
and electrolyte homeostasis in mammals, the regulator of body fluid endocrine nature of the avian heart has not yet been fully elucidated. In this
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study, five leghorn chicken hearts were examined. The intensity, distribution and ANP immunoreactivity of the myoendocrine cells in the different heart regions of the heart were investigated with light and electron microscopy, and through immunogold labeling of ANP with goat anti-human O-ANP antiserum. We have confirmed the existence of myoendocrine cells in the different regions of the avian heart. Myoendocrine cells were randomly scattered within the different heart regions without any predictable localization pattern. They had very small numbers of mature secretory granules and an atrophied secretory apparatus. In comparison to controls weak to nrgative ANP immunoreactivity was seen. These results might indicate a difference in amino acid sequence between avian and human ANP, or diminished role of ANP as a regulator of body and electrolyte homeostasis in birds.