Influence of Aminoethylisothiouronium Bromide·hydrobromide and Hypoxia on Recovery from Radiation Injury in Mice

Abstract

AMINOETHYLISOTHIOURONIUM bromide·hydrobromide (AET) and hypoxia appear to act as radiation dose reducers; that is, to obtain the same biological response to radiation, higher doses are required in the presence of these agents than in their absence. The ratio of the doses required to elicit the same response in the presence and in the absence of the protectant (protection ratio) is about the same for radiation-induced mortality, changes in the various elements of the haematopoietic system, and changes in spleen, thymus, and body-weights^1,2. The constancy of the protection ratio and recent cell culture studies³ imply that radiation injury produced under the two conditions is equivalent. Recent investigations in this laboratory, however, have suggested that the radiation injury may not be completely equivalent. In sheep, pentobarbital anaesthesia and assumed attendant hypoxia resulted in a mortality protection ratio of 1.4. However, recovery at 30 days as measured by the split-dose technique was significantly less in the anaesthetized group than in animals irradiated without anaesthesia^4,5. The present experiments with AET and hypoxia were conducted to determine the influence of protectants on initial injury and recovery from this injury. The term ‘recovery’ is used here to indicate the gradual return to normal radiosensitivity following a sub-lethal dose.