Cellular localization of monoamine oxidase A and B in human tissues outside of the central nervous system

We studied the localization of monoamine oxidase (MAO) A and B in human hea rt. liver, duodenum, blood vessels and kidney by immunohistochemistry. The primary antibodies used were mouse monoclonal antihuman MAO-A (6G11/E1) and anti-human MAO-B (3F12/G10/2E3). Samples were obtained from six routine au topsy cases and fixed in 2% paraformaldehyde. All cardiomyocytes and hepato cytes showed MAO-A and MAO-B immunoreactivity. In the duodenum, both immuno reactivities were present in all cells of the villi, Lieberkuhn crypts, mus cularis mucosae and muscular layers, whereas Brunner glands were devoid of MAO-A and MAO-B staining. Endothelial cells of lymphatic vessels showed MAO -A but no MAO-B immunoreactivity, whereas arteries and veins presented MAO- A and MAO-B staining in muscular layers and fibroblasts but not in endothel ial cells. In the kidney, renal tubuli showed MAO-A and MAO-B immunoreactiv ities, whereas collecting ducts and the Bowman's capsule showed only MAO-A staining. These data represent the first study of the cellular distribution of MAO-A and MAO-B in these human tissues. They show that both enzymes hav e a widespread distribution in the human body with a matching pattern in ma ny, but not all tissues, and with strong differences from the pattern of di stribution in rodents.