Nitric oxide synthase inhibition by L-NAME during repetitive focal cerebral ischemia in rabbits

The effects of nitric oxide synthase inhibition on brain acidosis, regional cortical blood flow (rCBF), and NADH redox state were examined using in vivo fluorescence imaging during four 15-min periods of moderate focal cerebral ischemia, each separated by three 5-min reperfusion periods followed by a final 3-h reperfusion period. Fasted rabbits under 1.5% halothane were divided into six groups of seven animals each: nonischemic controls, ischemic controls, and the following drug groups receiving NG-nitro-L-arginine methyl ester (L-NAME) intravenously 20 min before repetitive ischemia (as follows: 0.1 mg/kg, 1 mg/kg, 10 mg/kg, and 1 mg/kg + 5 mg/kg L-arginine). L-NAME at 0.1 and 1 mg/kg prevented the development of significant brain acidosis throughout the four ischemic insults. L-NAME at 10 mg/kg reduced preischemic rCBF by 21% (P < 0.05) and did not mitigate brain acidosis after the third and fourth ischemic insults. Brain intracellular pH returned toward baseline after the 3-h final reperfusion in all groups. NADH redox state was significantly (P < 0.05) elevated from baseline controls in all groups during the last three ischemic insults. During the final reperfusion period, NADH redox state returned toward baseline values only in the 0.1 mg/kg L-NAME and ischemic control group. In conclusion, low-dose L-NAME attenuated brain acidosis independent from rCBF changes during intermittent, moderate focal cerebral ischemia.