L-NIO is a non-selective inhibitor of all NOS isoforms. The Ki values for nNOS (rat), eNOS (bovine), and iNOS (mouse) are 1.7, 3.9, and 3.9 μM, respectively. L-NIO inhibits endothelial-dependent relaxation induced by acetylcholine in rat aortic rings and hypotensive responses to acetylcholine and bradykinin.