Inhibition of Thymidine-kinase-DNA-polymerase Activity in the Kidney by X-radiation before or after Uninephrectomy

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Abstract
Rats were exposed to whole-body X-radiation (850 rad) at time-intervals either before or after unilateral (left) nephrectomy; the remaining (right) kidney was removed 48 hours after nephrectomy. The specific activity of the kidney enzymes (thymidine-kinase-DNA-polymerase system) catalysing DNA-synthesis was assayed in vitro. The ratio of enzyme activities in the right versus left kidney was profoundly suppressed in rats irradiated 10 min to 18 hours after uninephrectomy (values < 1); irradiation 19 to 24 hours after unilateral nephrectomy resulted in a sharp rise in these ratios (values up to 6.6). Radiation exposure effected 15 min to 22 hours before uninephrectomy depressed these ratios (1 to 0.05). Further evidence suggests that partial recovery from this latent radiation damage can occur if the time-interval between irradiation and uninephrectomy is sufficiently prolonged. The data indicate that the early steps in the induction of the thymidine-kinase-DNA-polymerase enzyme system are highly radio-sensitive.