CHANGES OF BIOLOGICAL REDUCING ACTIVITY IN RAT-BRAIN FOLLOWING CLOSED-HEAD INJURY - A CYCLIC VOLTAMMETRY STUDY IN NORMAL AND HEAT-ACCLIMATED RATS

Reactive oxygen species (ROS) are normally generated in the brain duri ng metabolism, and their production is enhanced by various insults. Lo w molecular weight antioxidants (LMWA) are one of the defense mechanis ms of the living cell against ROS. The reducing capacity of brain tiss ue (total LMWA) was measured by cyclic vol tammetry (CV), which record s biological oxidation potential specific to the type of scavenger(s) present and anodic current intensity (I-a), which depends on scavenger concentration. In the present study, the reducing capacity of rat bra in following closed head injury (CHI) was measured. In addition, CV of heat-acclimated traumatized rats was used to correlate endogenous cer ebroprotection after CHI with LMWA activity. Sham-injured rat brains d isplayed two anodic potentials: at 350 +/- 50 mV (I-a = 0.75 +/- 0.06 mu A/mg protein) and at 750 +/- 50 mV (I-a = 1.00 +/- 0.05 mu A/mg pro tein). Following CHI, the anodic waves appeared at the same potentials as in the sham animals. However, within 5 min of CHI, the total reduc ing capacity was transiently decreased by 40% (p < 0.01). A second dip was detected at 24 h (60%, p < 0.005). By 48 h and at 7 days, the I-a levels normalized. The acclimated rats displayed anodic potentials id entical to those of normothermic rats. However, the I-a of both potent ials was lower (60% of control, p < 0.001). The I-a profile after CHI was the direct opposite of the normothermic I,profile: no immediate de crease of I-a and an increase from 4 h and up to 7 days (40-50%, p < 0 .001). We suggest that the lowered levels of LMWA in the post-CHI peri od reflect their consumption due to overproduction of free radicals. T he augmented concentration of LMWA found in the brain of the heat-accl imated rats suggests that these rats are better able to cope with thes e harmful radicals, resulting in a more favorable outcome following CH I.