Effect of CO(2) on labelling of nerve and liver cells by nucleic acid precursors.

In vivo experiments in mice demonstrated that 5% CO(2) content in the air inhaled did not change the labelling in autoradiograms from animals injected with [(3)H]uridine, [(3)H]orotic acid, [(3)H]hypoxanthine, [(3)H]lysine or [(3)H]cytidine. At 20% CO(2) content there was a significant decrease in labelling of brain cells with [(3)H]uridine and [(3)H]cytidine, but not following [(3)H]lysine; there was no labelling of nerve cells with [(3)H]orotic acid or [(3)H]hypoxanthine, but a control group was not included. The labelling of choroid plexus and hepatocytes was independent of the CO(2) concentration. A comparison of in vivo and in vitro experiments at 20% CO(2) content showed a similar significant decrease in labelling of brain cells with [(3)H]uridine and [(3)H]cytidine. It is concluded that a metabolic change is the most appropriate explanation of the CO(2) effect.