Effect of Head X-Irradiation on the Uptake of Radiophosphorus by Rat Brains. ∗

Conclusions

Whole head irradiation in rats with 20 Krad increases P³² uptake by the brain. These findings confirm the results of Stajic et aL(8), and strongly suggest that ionizing radiation enhances the permeability of the BBB to phosphate. By introducing the time parameter in our study, we also were able to approximate the time of onset of the permeability change. It begins after a delay of at least 24 hours after exposure to irradiation. This delay time explains the negative findings of Florsheim et al(S), who could not have detected the delayed effect because of the temporal arrangement of their experiments. It now must be determined if ionizing radiation of the whole brain or its parts increases the permeability to other molecules, particularly to biogenic amines, and whether whole head irradiation affects the permeability of the brain in toto or whether there are loci of predilection in their reaction to X-ray treatment.