We sought to determine whether expression of the inducible, calcium-independent isoform of nitric oxide synthase (iNOS) contributes to the tissue damage produced by focal cerebral ischemia. The middle cerebral artery was occluded in halothane-anesthetized spontaneously hypertensive rats. Twenty-four hours later rats received intraperitoneal injections of the iNOS inhibitor aminoguanidine (100 mg/kg twice per day; n = 10) or of aminoguanidine + L-arginine (300 mg/kg four times per day; n = 7), aminoguanidine + D-arginine (n = 7), arginine alone (n = 6), or vehicle (n = 9). Drugs were administered for 3 consecutive days. Infarct volume was determined by image analysis in thionin-stained brain sections 4 days after induction of ischemia. Administration of aminoguanidine reduced infarct volume by 33 +/- 4% (P < 0.05 from vehicle; analysis of variance and Tukey's test), a reduction that was antagonized by coadministration of L- but not D-arginine. Administration of L-arginine alone did not affect infarct size (P > 0.05 vs. vehicle). In separate rats (n = 10), aminoguanidine attenuated calcium-independent NOS activity in the infarct (P < 0.05 vs. vehicle) without affecting calcium-dependent activity (P > 0.05). Aminoguanidine did not affect resting cerebral blood flow or the cerebrovascular vasodilation elicited by hypercapnia, as determined by laser-Doppler flowmetry (n = 4). We conclude that aminoguanidine selectively inhibits iNOS activity in the area of infarction and reduces the volume of the infarct produced by middle cerebral artery occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)
