Nitric oxide synthase inhibitors 7- and 6-nitroindazole relax smooth muscle in vitro

7-Nitroindazole induced concentration-dependent relaxation of precontracted rabbit aorta, dog middle cerebral artery, rat anococcygeus muscle and rat stomach fundus. Relaxations to 7-nitroindazole in rabbit aorta were unaffected by nitric oxide synthase blockade or endothelial removal. 6-Nitroindazole also caused concentration-dependent relaxation in dog middle cerebral artery and rabbit aorta, being equipotent with 7-nitroindazole in both tissues. These data suggest that indazole derivatives can induce an endothelium- and nitric oxide synthase-independent relaxation of smooth muscle in vitro.