| Research Abstract |
Adrenomedulin (AM) is a potent vasorelaxant peptide recently isolated from human pheochromocytoma tissue, and is structurally a member of CGRP family. mRNA of AM is highly expressed in several tissues including heart, lung, kindey and vascular wall as well as adrenal medulla. In this project, we have studied the expression and secretion of AM and its signal transduction.
To investigate the sites of production and secretion of AM in heart failure, we measured plasma adrenomedullin levels and peptide and mRNA levels of adrenomedullin in various tissues in rats with heart failure. We also examined whether the heart actually secretes AM into the circulation in patients with heart failure. Plasma AM levels were increased in heart failure rats, correlating with ventricular weight. Tissue AM peptide and mRNA levels were increased in the heart and lungs, but not kidney or adrenals of rats with heart failure. Plasma AM levels were higher in the coronary sinus than in the aorta in patients with h
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eart failure. These results suggest that plasma adrenomedullin levels are increased in heart failure in proportion to its severity and that cardiac production and secretion of adrenomedullin is increased in heart failure rats. Lungs may be another site for increased production of adrenomedullin in heart failure rats.
To elucidate the regulatory mechanism of human AM gene expression, functional elements of 5'-flanking region of AM gene were examined in cultured human aortic endothelial cells (HAEC) by using a luciferase vector. The promoter activity of AM gene 5'-flanking DNA was reduced by losing NF-IL6 site at -85 to -93 bp, AP-2 sites at -33 to -68 bp and TATA box at -21 to -26 bp. These cis-acting elements are supposed to participate in the transcriptional regulation of human AM gene in EC
It is still unclear whether AM-induced vasodilation is endothelium-dependent. Endothelium-denudation of the aortic ring suppressed the dilatory response to AM.Furthermore, pretreatments of the rat aortic rings and isolated kidney with E-4021, a cGMP specific phosphodiesterase inhibitor, significantly enhanced AM-induced vasodilation, suggesting an important role of NO-cGMP in the vascular action of AM.
Proadrenomedullin N-terminal 20 peptide (PAMP-20) is a potent hypotensive peptide processed from the AM precursor. We have identified PAMP-12 (PAMP[9-20]) porcine adrenal medulla as a major product of the AM precursor, and demonstrated that it exhibits a potent hypotensive action. Although the existence of a specific receptors for PAMP remains obscure, PAMP-12 might share a biological functin with PAMP-20 Less
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