[Effect of ionizing radiation on cerebral phosphodiesterase]

The authors examined the influence of x-ray irradiation on phosphodiesterase system in the brain of rats and the sensitivity of the enzyme to inhibitors (caffeine, theophyline, thyopental) and activators (imidozol). The animals (Wistar with weights of 150--200 gm/were irradiated singly with a dose of 737 r. Phosphodiesterase activity (PD) was determined by the method of Filburn and Carn (1972) at two substrate concentrations (1 and 100 microM). X-ray irradiation did not change PD with high Km, while the enzyme with low Km was reduced significantly and transitionaly. Caffeine, theophyline and thyopental inhibited more PD with low Km in the irradiated rats in comparison with the control nonirradiated rats. The activating effect of imidazol on PD with low Km was more marked in irradiated rats. These data could be interpreted in the light of the molecular mechanisms, determining the altered action of some drugs after x-ray irradiation.