In vivo measurement of superoxide in the cerebral cortex during anoxia-reoxygenation and ischemia-reperfusion.

Abstract. The exact time profile of superoxide generation during anoxia-reoxygenation and ischemia-reperfusion was assessed in the feline cerebral cortex in vivo using a chemiluminescence technique with a probe specific for superoxide, 2-methyl-6-[p-methoxyphenyl]-3,7-dihydroimidazo[1,2-alpha]pyrazin-3-one (MCLA). MCLA solution was superfused on the cortex throughout the protocol, and MCLA chemiluminescence was measured using a newly developed photon counting system. Reflectance at 398 nm was simultaneously measured to compensate for hemodynamic artifacts resulting from cerebral blood volume changes. In 19 animals, a 90-second anoxia was induced by the inhalation of 100% nitrogen followed by a 40-minute reoxygenation. The chemiluminescence decreased during the period of anoxia (p < 0.01) and then exceeded the baseline level at 15 and 20 minutes after reoxygenation (p < 0.05). In six animals, superoxide dismutase (SOD) was continuously superfused and anoxia-reoxygenation was performed in the same manner. The chemiluminescence decreased during the period of anoxia (p < 0.05) but did not exceed the baseline level during the reoxygenation period, indicating that an increase in superoxide production was the main cause of the chemiluminescence increase. In eight animals, a 15-minute forebrain ischemia was induced by the occlusion of the bilateral common carotid arteries with systemic hypotension (systolic blood pressure less than 50 mmHg) followed by a 30-minute reperfusion. The chemiluminescence decreased during the period of ischemia (p < 0.01) and then increased at 20 and 25 minutes after reperfusion (p < 0.05). These results indicate that superoxide generation decreases during anoxia and ischemia and then increases within 20 minutes after reoxygenation or reperfusion.