P-31 NMR IN-VIVO STUDY OF THE ACUTE EFFECTS OF DIFFERENT DOSES OF GAMMA-RADIATION ON RAT-BRAIN PHOSPHATE-METABOLISM

Changes in relative levels of brain phosphates and intracellular pH at selected time intervals after total gamma-irradiation of a rat at a s ingle dose of 6.5 or 300 Gy were studied by P-31 NMR in vivo. Irradiat ion yielded only minor changes in the spectra. Irradiation at a dose o f 6.5 Gy caused a reversible decrease in P-i and an alkaline pH shift of 0.2 units after day 1, with no change in ATP. The signal, which con sisted of alpha-ATP, alpha-ADP, NAD(+)/NADH and diphosphodiesters, dec lined after day 6, possibly due to a fall in NAD(+)/NADH concentration . Irradiation at a dose of 300 Gy led to all increase in ATP from 10 t o 13% of total phosphates after day 1. Homeostasis of brain energy met abolism was characterized by the Z-index (normalized sample correlatio n coefficients averaged over the correlation matrix for NMR-measured p hosphomonoesters, P-i, pH, phosphocreatine, gamma-ATP + beta-ADP, alph a-ATP + alpha-ADP + NAD(+)/NADH + diphosphodiesters and beta-ATP). The Z value rose from -0.18 +/- 0.02 to -0.02 +/- 0.02 by day 6 or from - 0.19 +/- 0.02 to -0.07 +/- 0.02 by day 1 after irradiation at a dose o f 6.5 or 300 Gy, respectively. This may indicate a pathological state of brain energetics as a system and a decrease in its stability.