DISTRIBUTION OF NITRIC-OXIDE SYNTHASE ACTIVITY IN ARTERIOLES AND VENULES OF RAT AND HUMAN INTESTINE

NO is produced within peripheral blood vessels through the action of t he differentially distributed constitutive and inducible NO synthase i soforms in the vessel wall. As in other sites in the periphery, NO exe rts local vasodilatory actions in the gastrointestinal microvasculatur e and is proposed to play a role in enteric vasomotor regulation. Usin g NO synthase histochemistry and endothelial cell immunohistochemistry , we provide the first anatomic evidence of NO synthesis in both endot helial and smooth muscle cells of submucosal blood vessels in the rat and human intestine. The findings of this study indicate that 1) as in the periphery, both the endothelial and vascular smooth muscle cells of the microvessels irrigating the rat and human intestinal wall posse ss NO synthesis potential, 2) NO synthase activity is predominantly lo calized to discrete subcellular patches, and 3) the source of NO withi n the vascular wall, either intimal or medial, should be a considerati on in future studies in terms of the relative contribution of these so urces to vasomotor tone in the rat and human gut wall.