Effect of moderate level x-radiation to brain on cerebral glucose utilization

The effect of x-radiation in doses used in treatment of brain malignancies has previously been established largely by histologic examination of the tissue or by observation of a deficit in function. At moderate dose levels such effects are usually delayed and are vascular in origin. We have used the 2-[14C]deoxyglucose method for the quantitative measurement of local cerebral glucose utilization to learn whether x-radiation administered to rat brain in a dose below that which is known to result in any histologic change may nevertheless affect the brain's local rates of glucose utilization. Measurements were made 4 days and 4 weeks after exposure of groups of rats to 1,500 rad. Rates of glucose utilization in 54 gray and eight white matter structures in both groups were compared with rates in sham-irradiated controls. Statistically significantly lower rates were found in 16 structures in rats 4 days after radiation and in 25 structures 4 weeks after radiation exposure. A weighted average rate for the brain as a whole was approximately 15% below that of the controls for both radiated groups, but this difference was short of being of statistical significance. It is clear from this study that the metabolic rates of some brain structures are reduced following moderate doses of x-radiation.