Some Theoretical Considerations of Changes in Tissue Enzyme Activity after Whole-Body X-Irradiation of Animals

To allow proper interpretation of enzyme changes, it is recommended that in vivo studies of the effects of x irradiation on tissue enzymes, particularly in the spleen and thymus, be carried out with the following considerations in mind. The weight and nitrogen changes in the organs should be reported as well as the specific activity of any enzyme studied, based preferably on nitrogen content, for each post-irradiation period examined. This would facilitate the interpretation of the changes in the specific and total activities of the enzyme and permit a comparison of results obtained in different laboratories. In addition, it is recommended that studies be carried out, if possible, using a variety of radiation doses and time intervals after irradiation, and each study should be assessed according to the principles outlined. It should be noted that many of the spleen enzymes which have been studied thus far exhibit moderate increases in specific activity following wholebody irradiation of rats and mice. These increases reflect, for the most part, only an increased concentration or enrichment of the enzymes with respect to nitrogen due to the marked loss of general cell nitrogen which accompanies splenic involution. We conclude, then, that increases in the specific activities of spleen enzymes may be more the rale than the exception and that many of these increases are only an indirect expression of the effect of whole-body x irradiation on the spleen. (auth)