Effect of misonidazole on the tolerance of the rat spinal cord to daily and multiple fractions per day of X rays.

The effect of misonidazole on the induction of early and late delayed radiation damage in the rat cervical spinal cord has been determined for single doses, daily, and multiple fractions per day of X rays. Paralysis occurred in two separate waves, which could be attributed to histologically different types of damage. Administration of misonidazole before irradiation did not modify the early and late delayed radiation response of the spinal cord. This suggested that the targets for misonidazole and radiation toxicity in the central nervous system are different. Comparison of different types of anaesthesia, Nembutal and Ethrane, with or without breathing oxygen, indicated that hypoxia was not induced in the spinal cord by the experimental conditions. Irradiation with two or three fractions a day showed a reduction in spinal cord tolerance, but this reduction became less with decreasing doses per fraction.