Is bradykinin (BK) a physiological vasodilator in the gut?

The physiological role of bradykinin (BK) as a mesenteric vasoregulator was explored. This nonapeptide is a potent vasodilator substance when administered exogenously in multiple in vivo models and is a smooth muscle relaxant when added to in vitro preparations. BK is naturally occurring in the gut wall. The substrate for BK, as well as the biosynthetic and metabolizing systems are present in the blood, the vascular wall, immunological cells, and perivascular neurons. BK B2 and B1 receptors have been characterized with sympathetic agonist and antagonist substances, and the receptors are present on mesenteric endothelial cells and myocytes. BK interacts with multiple endogenous mesenteric vasodilator mediators, such as nitric oxide, prostacyclin, and neuropeptides. Taken together this evidence supports the functional importance of BK as a normal vasodilator in the gut.