Induction of rat kidney ornithine decarboxylase by nicotinamide without a concomitant increase in DNA synthesis

Four hours after an i.p. injection of 500 mg/kg nicotinamide,there was a decrease in kidney ODC activity, followed by a substantialincrease by 24 h. Exposing rats to 0, 0.67, 6.7 and 30 mM nicotinamidein their drinking water for 7 and 28 days also resulted in astatistically significant increase in kidney ODC activity, butthe rates of DNA synthesis were unaffected, as measured by incorporationof [³H]thymidine into DNA and % labeled proximal tubule nuclei;the total amount of DNA/kidney was also unaffected. The resultsof this investigation demonstrate that nicotinamide, a knownrenal tumor promoter, was able to induce a significant increasein ODC activity in the rat kidney without a concomitant increasein DNA synthesis, suggesting that early stimulation of ODC isassociated with tumor promotion even in the absence of effectson DNA replication.