The auricular myocardiocytes of the heart constitute an endocrine organ. Characterization of a porcine cardiac peptide hormone, cardiodilatin-126.

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 gel-permeation and ion-exchange chromatography, and high performance liquid chromatography. During the isolation procedure, other peptides of smaller molecular weight were also found, which, in relation to cardiodilatin-126 (CDD-126), are shorter at their N-terminal. Among these, CDD-88 has also been isolated and characterized, and has been established as a prominent member of the cardiac hormone family. The N-terminal and C-terminal segments of the 126 amino acid-containing molecule were synthesized and used to raise region-specific 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, cardiodilatin-126 and cardiodilatin-88 possess qualities of a significant hormone family regarding the regulation of extracellular fluid volume and blood pressure.