INHIBITION OF THYMIDINE KINASE - DNA POLYMERASE ACTIVITY IN THE KIDNEY BY X-RADIATION BEFORE OR AFTER UNINEPHRECTOMY

Rats were exposed to whole-body X radiation 850 rad at various times before or after unilateral nephrectomy, and the other kidney was removed 48 hours later. The kidneys were homogenized in isotonic sucrose-tris buffer, and the homogenate was centrifuged at 105,000xg for 1 hour. The supernatants were assayed in vitro for the DNA polymerase enzymes which catalyze the incorporation of H3-thymidine into DNA. The accumulation of these enzymes was profoundly suppressed in rats irradiated at 10 minutes to 18 hours after uninephrectomy when irradiated between 19 and 24 hours after nephrectomy was a sharp rise in enzyme activity. When irradiation was carried out between 15 minutes and 22 hours before uninephrectomy, enzyme activity was also profoundly suppressed. The data indicate that the early steps in the induction or formation of the thymidine kinase-DNA polymerase enzyme system are highly radiosensitive.