To elucidate the secretory form of atrial natriuretic polypeptide from the atrium, the molecular form of atrial natriuretic polypeptide in the perfusate from the isolated beating rat heart and in plasma taken at the coronary sinus of 10 patients during cardiac catheterization has been investigated using high performance gel permeation chromatography and reverse phase high performance liquid chromatography coupled with radioimmunoassay for atrial natriuretic polypeptide. Atrial natriuretic polypeptide in the perfusate from the rat heart showed a single peak eluting at the position of a low molecular weight form of atrial natriuretic polypeptide, without any detectable amounts of atrial natriuretic polypeptide with high molecular weights. The major component of atrial natriuretic polypeptide in the rat heart perfusate co-migrated with rat α-atrial natriuretic polypeptide in reverse phase high performance liquid chromatography. In 9 out of 10 patients atrial natriuretic polypeptide in plasma taken at the coronary sinus revealed a single peak of atrial natriuretic polypeptide emerging at the position of human α-atrial natriuretic polypeptide in gel filtration. Only one plasma sample had a small quantity of high molecular weight forms with the predominant low molecular weight form of atrial natriuretic polypeptide. The major component of atrial natriuretic polypeptide in the plasma extract from the coronary sinus was identified with human α-atrial natriuretic polypeptide. These results indicate that α-ANP, a 28-amino acid polypeptide, is secreted as a cardiac hormone into the coronary blood stream from the atrium.
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