Comparative aspects of the endocrine myocardium.
Secretory organelles are common features of the myocardium, from cyclostomes to man, and occur in the atria of all vertebrates, in the ventricle of the lower vertebrates and in the embryonic and foetal ventricles of mammals. These organelles constitute the final step in the regulated secretory pathway for the atrionatriuretic polypeptides collectively termed atriopeptins. At birth, however, the mammalian ventricle shifts to constitutive secretion, with low levels of atriopeptins in the normal and elevated levels in the hypertrophied adult ventricle. In the mammalian atria the atriopeptins are costored with the calcium-binding, highly acidic chromogranins A and B, and the secretory organelles account also for the highest subcellular calcium concentration in the myocardium. These similarities between the myocardium and the neuroendocrine system confirm and extend the earlier observations and point to new aspects of the endocrine heart; as a source of prohormones not only for the atriopeptins but also for members of the chromogranin family. A significant role is also apparent for the secretory organelles in the intracellular sequestration of calcium in both the normal and the overstimulated myocardium. Down-regulation of excess in blood volume appears to be mediated by atriopeptins via indirect and direct relaxations of vascular smooth muscle in the aorta and other large arteries. Apart from their natriuretic actions, the atriopeptins also contribute to substantial fluid loss via the gastrointestinal tract.
Aardal
S
S
Department of Physiology, University of Bergen, Norway.
Helle
K B
KB
D000818:Animals; D009320:Atrial Natriuretic Factor / Q000378:metabolism / Q000502:physiology*; D001810:Blood Volume / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002864:Chromogranins / Q000378:metabolism / Q000502:physiology; D003594:Cytoplasmic Granules / Q000378:metabolism; D015536:Down-Regulation; D004702:Endocrine Glands; D006321:Heart / Q000502:physiology*; D006325:Heart Atria / Q000378:metabolism; D006352:Heart Ventricles / Q000378:metabolism; D006801:Humans; D009206:Myocardium / Q000166:cytology*; D011499:Protein Processing, Post-Translational; D014714:Vertebrates / Q000033:anatomy & histology*
D002864:Chromogranins; D009320:Atrial Natriuretic Factor; D002118:Calcium