Redox behavior of cytochrome oxidase in the rat brain measured by near-infrared spectroscopy

Hoshi, Yoko, Osamu Hazeki, Yasuyuki Kakihana, and MamoruTamura. Redox behavior of cytochrome oxidase in the rat brain measured by near-infrared spectroscopy. J. Appl.Physiol. 83(6): 1842-1848, 1997.Usingnear-infrared spectroscopy, we developed a new approach for measuringthe redox state of cytochrome oxidase in the brain under normalblood-circulation conditions. Our algorithm does not require theabsorption coefficient of cytochrome oxidase, which differs from studyto study. We employed this method for evaluation of effects of changesin oxygen delivery on cerebral oxygenation in rats. When fractionalinspired oxygen was decreased in a stepwise manner from100 to <10%, at which point the concentration of oxygenatedhemoglobin([HbO₂])decreased by ~60%, cytochrome oxidase started to be reduced.Increases in arterial PO₂ underhyperoxic conditions caused an increase in[HbO₂], whereas further oxidation of cytochrome oxidase was not observed. The dissociation of the responses of hemogloblin and cytochrome oxidase wasalso clearly observed after the injection of epinephrine under severelyhypoxic conditions; that is, cytochrome oxidase was reoxidized withincreasing blood pressure, whereas hemoglobin oxygenation was notchanged. These data indicated that oxygen-dependent redox changes incytochrome oxidase occur only when oxygen delivery is extremelyimpaired. This is consistent with the in vitro data of our previousstudy.