Equine cardiodilatin atrial natriuretic peptide - Primary structure and immunohistochemical localization in auricular cardiocytes

Cardiodilatin (CDD)/atrial natriuretic peptide (ANP) is a 28-amino acid pep tide hormone known to be synthesized in the heart of a large number of diff erent vertebrates. It plays an important role in the regulation of blood pr essure and natriuresis/diuresis. Since the cardiovascular system of the hor se has to meet the highest requirements concerning its physiological perfor mance, we intended to characterize the cardiodilatin/atrial natriuretic pep tide system of this species. By means of immunohistochemistry and immunoele ctron microscopy, we precisely identified auricular cardiocytes as the loci of CDD/ANP synthesis. Using aortic smooth muscle relaxation assay and CDD/ ANP-ELISA, we succeeded in isolating the biologically active prohormone. We subsequently cloned the equine cDNA of the CDD/ANP precursor protein and d educed its primary sequence. The entire precursor protein is in good agreem ent with the CDD/ANP prohormones of other mammals. The deduced theoretical average M-r of equine CDD/ANP-1-126 is 13,764, corresponding to the molecul ar weight of purified peptide determined by ESI-MS. Our findings suggest th at equine CDD/ANP is produced in auricular cardiocytes and the predominant storage form of CDD/ANP in the auricle is the prohormone CDD/ANP-1-126.