The Effect of Ionizing Radiation upon Mitochondria of the Central Nervous System.

The respiratory rate in the presence of substrate + ADP (state 3) and after the conversion ADP yields ATP (state 4) was studied in the mitochondria of the rat brain after irradiation of the rats' heads with an electron linear accelerator. After 20,000 rads irradiation there was a transient diminution of respiratory control (state 3/state 4) when glutamate was used as the substrate, but no abnormalities were seen when succinate was the substrate. Irradiation with 10,000 rads had no effect upon the respiratory rate or respiratory control. The addition of DPNH to irradiated mitochondria had no effect upon mitochondrial respiration as compared to controls. Irradiation of the brain with 20,000 rads failed to produce significantly greater peroxidation than in sham irradiated mitochondria and failed to produce greater swelling in irradiated mitochondria, even in the presence of FeNH4SO4 or ascorbate. The slight and transient changes in respiratory control produced by irradiation in brain mitochondria are in marked contrast to the susceptibility of mitochondria from other organs. The comparative radioresistance of brain mitochondria may be the result of greatly diminished radiation-induced perioxidation of mitochondrial membranes. (Author Modified Abstract)