Morphogenesis and reaction to hypoxia of atrial myoendocrine cells in chick embryos (Gallus gallus)

Ultrastructural and stereomorphometric study of the chick embryo right atrium at the 14th day of incubation has shown cardiomyocytes to divide mitotically and to be at different stages of differentiation. The cytoplasm of some muscle cells contains secretory granules that by sizes and morphology can be classified as formed, mature, and dissolved forms. By the 18th day of incubation the majority of cardiomyocytes is already differentiated, and the amount of their secretory granules increases. Under conditions of hypoxia, after three days, in myoendocrine cells there are noted features of accelerated secretion of the peptides that are synthesized earlier and are accumulate in the granules, while after one weak—features of acceleration of their synthesis. It can be concluded that in chick embryos, at least from the 14th day of incubation, the system of the heart natriuretic peptides participates in regulation of hemodynamics and of water—salt balance and responds to hypoxia.