Heme oxygenase activity and immunohistochemical localization in bovine pulmonary artery and vein

Recent studies suggest that carbon monoxide (CO) derived from heme oxygenase (HO)-catalyzed metabolism of heme plays a role in the regulation of cell function and communication. In blood vessels, CO may regulate vascular smooth-muscle tone through the activation of soluble guanylyl cyclase, in a manner similar to that of nitric oxide. The objective of this study was to determine the relation between HO enzymatic activity and localization of HO protein in bovine pulmonary blood vessels. HO enzymatic activity was determined by quantitating the rate of CO formation in the microsomal fraction of homogenates of bovine pulmonary artery (BPA) and vein (BPV). HO protein was localized by immunohistochemical analysis of paraformaldehyde-fixed tissue by using polyclonal antibodies to inducible HO (HO-1) and noninducible HO (HO-2). HO enzymatic activity was measured in BPA and BPV, which correlated with the presence of HO protein. In BPA, HO enzymatic activity was found in the adventitia and medial layer; HO protein was localized in the nerves and vasa vasorum of the adventitia and was found throughout the smooth-muscle cells in the medial layer. The data clearly demonstrate the presence of HO enzymatic activity for the formation of CO in blood vessels that contain HO protein.