Incomplete cerebral ischemia in the rat: vascular and metabolic changes as measured by infrared transillumination in vivo.

Cerebral blood volume, hemoglobin saturation and the cytochrome a, a3 redox state were monitored simultaneously by using three wavelengths of light in the near infrared portion of the spectrum for transillumination of the intact skull of rats. The changes in these parameters following incomplete cerebral ischemia were assessed in Wistar and Long-Evans rats submitted to carotid ligation. Another group of Wistar rats was submitted to vertebral + carotid occlusion. The experiments, performed under N2O/O2 anesthesia, showed that in all three groups carotid occlusion induced a decrease in blood volume, Hb saturation and a reduction of cyt. a, a3. However, the cytochrome redox state tended to normalize during ischemia as a consequence of higher O2 extraction from blood. The primary finding of this study was the marked hyperoxidation of cyt. a, a3 which occurred after reestablishing of the carotid blood supply, in spite of a secondary post-ischemic hypoperfusion of the brain. Although uncoupling of oxidative phosphorylation cannot be excluded the dissociation between blood supply and metabolism could well be due to ischemia-induced hypermetabolism of the central nervous tissue. In view of the marked oxidation of cyt. a, a3 during the reperfusion period as compared with the small extent of its reduction during the ischemic episode, the data also support the hypothesis that under steady state conditions in vivo, cytochrome oxidase is mainly reduced.