Influence of Protein Nutrition on Dose-Survival Relationship Following Rat Kidney Irradiation

Immediately following unilateral nephrectomy the remaining kidney of juvenile male Sprague-Dawley rats was sham irradiated or irradiated to doses of 14-30 Gy. Following irradiation the animals were placed on isocaloric diets of either 20 or 4% protein. Median life spans for the animals on the low protein diet were significantly increased compared to the median life spans on the 20% protein diet. Serum urea nitrogen (SUN) levels were periodically measured in rats from each of the experimental groups. SUN levels in the irradiated rats fed the 20% protein diet increased significantly over unirradiated controls as a function of time. In contrast animals fed the 4% protein diet showed no significant changes in SUN levels irrespective of the size of radiation dose and time post irradiation. Renal protective factors calculated as the ratio of 80% survival times for animals fed the 20% protein diet compared to animals fed the 4% protein diet can be calculated to be 2.3 at 18 Gy and 2.8 at 22 Gy. Likewise, a SUN protective factor calculated as the ratio of percentage of nonirradiated control SUN values for the two diets$ \smallmatrix \underline{({\rm SUN}\ 20\%\ \text{irradiated})} \\ \underline{({\rm SUN}\ 20\%\ \text{nonirradiated})} \\ \underline{({\rm SUN}\ 4\%\ \text{irradiated})} \\ \underline{({\rm SUN}\ 4\%\ \text{nonirradiated})} \endsmallmatrix $is 2.4 for 18 Gy and 3.9 for 22 Gy.