Nitric oxide synthase inhibition alters cerebral blood flow and oxygen balance in focal cerebral ischemia in rats.

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Abstract
This study investigated whether the nitric oxide synthase inhibitor NG-nitro-L-arginine-methyl ester (L-NAME) would alter blood flow and oxygen balance in the ischemic cerebrocortex of isoflurane-anesthetized Long-Evans rats. Fifteen minutes after middle cerebral artery occlusion, L-NAME (1.5 mg/min per kilogram) was infused intravenously to the L-NAME group (n = 14), and normal saline was given to the control group (n = 14) for 45 minutes. In each group, regional cerebral blood flow was determined with [14C]iodoantipyrine, and arterial and venous oxygen saturations were determined by microspectrophotometry. In both groups regional cerebral blood flow of the ischemic cortex was significantly lower than that of the contralateral cortex ([mean +/- SD] 55 +/- 13 versus 110 +/- 29 mL/min per 100 g in the control group and 35 +/- 13 versus 90 +/- 24 mL/min per 100 g in the L-NAME group). Compared with the blood flow in the ischemic cortex of the control group, L-NAME significantly reduced ischemic blood flow by 36%. Venous oxygen saturation was significantly increased in the ischemic cortex (41 +/- 1% versus 44 +/- 3%) but decreased in the contralateral cortex (65 +/- 3% versus 61 +/- 4%) by L-NAME. Calculated ischemic cortical oxygen consumption in the L-NAME group was 39% lower than that in the corresponding control group, whereas the difference was only 11% in the contralateral sides between groups. In both groups, the ratio of oxygen supply to consumption was lower in the ischemic than in the nonischemic regions. In the ischemic cortex, this ratio was significantly lower in the control group than in the L-NAME group (1.7 +/- 0.1 versus 1.9 +/- 0.1). In contrast, the ratio tended to be decreased by L-NAME in nonischemic regions. These observations suggest that despite a decrease in cerebral blood flow, inhibition of nitric oxide synthesis mildly improves the oxygen supply and consumption balance in the ischemic cortex.