Generation of nitric oxide and superoxide during reperfusion after focal cerebral ischemia in rats

We investigated the levels of nitrosyl hemoglobin (HbNO) in rat jugular blood by electron spin resonance (ESR) spectroscopy during and after middle cerebral artery occlusion. The levels of plasma nitric oxide (NO) end products, nitrite plus nitrate, were compared with the levels of HbNO. Small amounts of HbNO were detected in sham-operated rats (n = 4) and those subjected to 2 h of occlusion (n = 4), whereas nitrite plus nitrate was increased only in the latter (P < 0.01; vs. sham). Upon reperfusion after 2 h of occlusion, both HbNO and nitrite plus nitrate clearly increased after 15 min (n = 4) and 30 min (n = 6) reperfusion (P < 0.01; vs. occlusion). Administration of superoxide dismutase (5 mg/kg) significantly increased HbNO (P < 0.05) but not plasma nitrite plus nitrate (n = 5). The increase in HbNO and nitrite plus nitrate after 30 min of reperfusion was suppressed by administration of N-G-nitro-L-arginine methyl ester (20 mg/kg; n = 4, P < 0.01), and this suppression could be reversed by L-arginine (200 mg/kg) (n = 4). The present study clearly showed that the L-arginine-NO synthase pathway was activated during reperfusion after focal cerebral ischemia and indicated the involvement of a reaction between NO and superoxide during early reperfusion.