l‐Arginine dilates rat pial arterioles by nitric oxide‐dependent mechanisms and increases blood flow during focal cerebral ischaemia

l‐Arginine (≥ 30 mg kg−1, i.v.), but not d‐arginine (300 mg kg−1) administered 5 min after unilateral common carotid/middle cerebral artery occlusion increased regional cerebral blood flow (rCBF) within the dorsolateral ischaemic cortex in spontaneously hypertensive rats. l‐Arginine (300 mg kg−1) increased rCBF from 22 ± 2.7 to 33 ± 4% of baseline as measured by laser‐Doppler flowmetry. This increase may explain the ability of l‐arginine to reduce infarct size following focal cerebral ischaemia, as reported previously. The mechanism appears to be mediated by nitric oxide since topical l‐NAME (1 μm), a nitric oxide synthase inhibitor, decreased pial arteriole calibre from 115 ± 2.2 to 106 ± 0.9% of baseline following l‐arginine infusion (300 mg kg−1).