Dysfunction of nitric oxide in the spastic basilar arteries after subarachnoid hemorrhage

The function of nitric oxide in spastic cerebral arteries after subarachnoid hemorrhage (SAH) was angiographically investigated in dogs. On days 4 and 7, after two intracisternal injections of autologous blood, higher concentrations of L-arginine than those of endogenous L-arginine in the cerebrospinal fluid produced a transient vasodilation of the spastic basilar artery, whereas NG-monomethyl-L-arginine (L-NMMA) produced no significant vasoconstriction. The vasodilator effect of L-arginine after SAH was stronger on day 4 than day 7, but less than that in intact dogs. Vasopressin, which is known to activate the endothelial L-arginine pathway, could induce a vasodilation only after the treatment with L-arginine. Intracisternal injection of superoxide dismutase (SOD), which caused no effect by itself, enhanced the duration of the vasodilator effect of L-arginine on the basilar artery on day 4 and both the magnitude and duration of that effect on day 7. Thus, the basal release of nitric oxide was impaired after SAH, but the ability to synthesize nitric oxide in the vascular wall was not abolished. Enhancement of L-arginine's effect by SOD suggested that the inactivation of nitric oxide by superoxide anion contributed to the development of vasospasm.