Atrial natriuretic factor in the heart of the human embryo

The presence of atrial natriuretic factor (ANF) has been demonstrated in striated myocytes of the human embryonic heart as well as in the adult heart, by immunohistochemical and immunocytochemical methods. The postconceptional age of the embryos ranged from 8 to 9 weeks. At this early stage of development, shortly after the appearance of atrial granules in humans, ANF was localized both in the auricles and remaining parts of both atria. Immunostaining was intensified in the subendocardial areas. No immunoreactivity was observed in the developing ventricles. Immunogold electron microscopy of atrial myocytes showed that the ANF-containing atrial granules were distributed throughout the sarcoplasm, although they tended to accumulate in the paranuclear areas. Neither the Golgi apparatus nor the rough endoplasmic reticulum exhibited ANF immunoreactivity, indicating that immunoreactive ANF of the human embryonic atria is stored in the mature granules. These results indicate an endocrine function of the human embryonic atria.