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 cardiovas cular function. Although ADM was originally isolated from pheochromocy toma, ADM-like immunoreactivity has also been widely detected in vario us tissues, including the cardiovascular system. Based upon the report s that ADM mRNA and ADM-like immunoreactivity are present in the heart , the present study was designed to investigate the immunohistochemica l localization of ADM in the canine heart and aorta. In the canine hea rt, immunohistochemical examination revealed positive immunostaining w ithin the myocardia in both atria and ventricles. ADM immunoreactivity was observed within the cytoplasm of myocardium, and was widely distr ibuted in the peripheral cytoplasm. ADM immunoreactivity was more inte nse in the atria than in the ventricles. In the canine aorta, vascular smooth muscle cells of the aorta and vasa vasorum were also immunopos itive for ADM. ADM immunoreactivity was mostly localized in the perinu clear position within the smooth muscle cells. There was no immunoreac tivity in endothelium, endocardium, epicardium, adventitia, or connect ive tissues. The current study demonstrates for the first time that im munoreactive ADM by immunohistochemistry is present in the cardiovascu lar system. As ADM has hypotensive and vasorelaxing actions and circul ates in the body, ADM is a cardiovascular peptide hormone that may pla y an important role in the regulation of cardiovascular system.