Immunohistochemical localization of adrenomedullin in canine heart and aorta

Adrenomedullin (ADM) is a new endogenous hypotensive and vasorelaxing peptide that may play an important role in the regulation of cardiovascular function. Although ADM was originally isolated from pheochromocytoma, ADM-like immunoreactivity has also been widely detected in various tissues, including the cardiovascular system. Based upon the reports that ADM mRNA and ADM-like immunoreactivity are present in the heart, the present study was designed to investigate the immunohistochemical localization of ADM in the canine heart and aorta. In the canine heart, immunohistochemical examination revealed positive immunostaining within the myocardia in both atria and ventricles. ADM immunoreactivity was observed within the cytoplasm of myocardium, and was widely distributed in the peripheral cytoplasm. ADM immunoreactivity was more intense in the atria than in the ventricles. In the canine aorta, vascular smooth muscle cells of the aorta and vasa vasorum were also immunopositive for ADM. ADM immunoreactivity was mostly localized in the perinuclear position within the smooth muscle cells. There was no immunoreactivity in endothelium, endocardium, epicardium, adventitia, or connective tissues. The current study demonstrates for the first time that immunoreactive ADM by immunohistochemistry is present in the cardiovascular system. As ADM has hypotensive and vasorelaxing actions and circulates in the body, ADM is a cardiovascular peptide hormone that may play an important role in the regulation of cardiovascular system.