the auricular myocardiocytes of the heart constitute an endocrine organ characterization of a porcine cardiac peptide hormone cardiodilatin126 a peptide hormone was extracted from the porcine right atrium following a bioassay for differential vasorelaxant effects on smooth muscle strips from aorta and renal and inferior mesenteric arteries the isolation procedure included several steps of gelpermeation and ionexchange chromatography and high performance liquid chromatography during the isolation procedure other peptides of smaller molecular weight were also found which in relation to cardiodilatin126 cdd126 are shorter at their nterminal among these cdd88 has also been isolated and characterized and has been established as a prominent member of the cardiac hormone family the nterminal and cterminal segments of the 126 amino acidcontaining molecule were synthesized and used to raise regionspecific antibodies the natural peptide was then localized within myoendocrine cells of the right atrium where specific atrial granules are located renal effects of cardiodilation were studied in conscious dogs and showed strong diuretic and natriuretic activities according to our functional studies cardiodilatin126 and cardiodilatin88 possess qualities of a significant hormone family regarding the regulation of extracellular fluid volume and blood pressure