Gene Expression of Adrenomedullin in Canine Normal Tissues and Diseased Hearts
Adrenomedullin (AM), originally isolated from human pheochromocytoma, is a potent endogenous vasodilating and natriuretic peptide. The AM produced by the proteolytic cleavage of its precursor (Prepro-AM) consists of 52 amino acids and a COOH-terminal amide structure, which isthe common structure of the calcitonin gene-relatedpeptide superfamily. The prepro-AM has a unique 20 amino acid residues in the NH2 terminus, proadrenomedullin N-terminal 20 peptide (PAMP). The PAMP, a novel hypotensive peptide, inhibits catecholamine secretion from sympathetic nerve terminus. The purposes of this study were to determine the cDNA sequences of canine AM and PAMP, to investigate their tissue distribution, and to evaluate whether mRNA expression of canine AM increases in association with spontaneous cardiovascular diseases.
Total RNA was extracted from canine normal heart, and was used in the RT-PCR procedure to isolate prepro-AM cDNA. Sequence analysis of the isolated cDNA was conducted. The AM mRNA expressions in various tissues from 2 healthy Beagles were investigated by the RT-PCR. In addition, the mRNA levels of AM in the atria and ventricles obtained from 2 dogs with patent ductus arteriosus (PDA) and 6 dogs with chronic mitral valvular diseases (CMVD) were compared with those from normal dogs.
The canine prepro-AM cDNA sequence and deduced amino acids were 1,541 base pairs and 188 residues, respectively. The cDNA sequences of canine AM and PAMP showed high homologies with those of the other mammalian species. The expressions of AM mRNA were detectable in the various normal tissues. In the cardiac tissues from the dogs with PDA and CMVD, mRNA levels of AM were elevated similar to atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP).