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Adrenomedullin is a new bioactive peptide recently isolated from pheochromocytoma. We report on the rat adrenomedullin distribution and molecular forms in various tissues and plasma. Using a sensitive radioimmunoassay system for rat adrenomedullin, high concentrations of immunoreactive rat adrenomedullin were detected in adrenal gland, lung and cardiac atrium. In lung and atrium, the immunoreactivity concentration in rat was about 610 times higher than that in human. The mean plasma concentration of immunoreactive rat adrenomedullin was 3.60 f 0.34 fmol/ml (mean + S.D.). Analysis in adrenal gland, lung and atrium with reverse-phase and gel-filtration high-performance liquid chromatography showed that most immunoreactive rat adrenomedullin emerged as a single peak at a position exactly identical to that of the authentic rat adrenomedullin peptide, synthesized according to the sequence predicted from the cDNA.

Adrenomedullin (AM) is a novel hypotensive and vasodilator peptide. We previously examined the localization of AM in human, rat, and porcine tissues using a polyclonal antibody against synthetic human AM[40-52]. We demonstrated that AM is widely distributed in the endocrine and neuroendocrine systems, but not in the heart, kidney, or blood vessels, although high levels of AM mRNA were detected in the latter tissues. In this study, we further investigated the distribution of AM by using two newly developed monoclonal antibodies against synthetic human AM peptides, [12-25] and [46-52]. AM immunoreactivity was observed in cardiac myocytes, vascular smooth muscle cells, endothelial cells, and renal distal and collecting tubules. In addition, AM-immunoreactive (IR) cells were found in mucosal and glandular epithelia of the digestive, respiratory, and reproductive systems, as well as the endocrine and neuroendocrine systems. These findings indicate that AM-IR cells are more widely distributed in human tissues and suggest that AM might play multiple biological roles in humans.