EXPRESSION OF HEME OXYGENASE-2 (HO-2)-LIKE IMMUNOREACTIVITY IN RAT-TISSUES

Microsomal heme oxygenase (HO) is a cytochrome P-450-assisted oxidored uctase, which catalyzes the NADPH-dependent decomposition of heme to c arbon monoxide (GO), biliverdin, and iron. Recent evidence suggests th at CO, similar to nitric oxide (NO), may serve as gaseous biological s ignalling molecule, which acts by stimulating soluble guanylate cyclas e in target cells. In the present investigation, we report the HO-like immunoreactivity (LIR) pattern of the constitutive HO isozyme, HO-2, and compare the results with recently published data on constitutive N O-producing nitric oxide synthase (NOS) in rat tissues. HO-2-LIR was m ost consistently observed in connective tissue elements (fibrocytes/-b lasts and fibroblast-like cells, such as interstitial cells in the bow el), blood vessel wall constituents (arterial and venous endothelial c ells, vascular smooth muscle cells), visceral smooth muscle cells (air way musculature, myometrium, muscularis mucosae of the small intestine ), mesothelial cells of serous membranes and in select epithelial cell populations. HO-2-LIR was absent from the striated (skeletal and card iac) musculature. HO-2 had a more widespread distribution and its expr ession largely differs from that of NOS. HO-2-LIR and NOS appear to be co-expressed in vascular endothelial cells and in selected nerve cell populations of certain parasympathetic and probably sensory ganglia. Our data suggest potential CO and NO systems as interrelated regulator y pathways in the local paracrine and autocrine control of diverse fun ctional systems.