The effect of papaverine on the fate of thymidine phosphates in isolated mouse thymus cells

The burst of incorporation of 3H into DNA of mouse thymocytes during an incubation at 37° for 5 min. following a preincubation at 4° for 30 min. is markedly inhibited by papaverine (0.1 mM). This event is accompanied by an efflux of 3H into the medium, largely in the form of thymidine. No enhanced efflux of 3H is detected when DNA synthesis is blocked by hydroxyurea (1 mM). While it is uncertain that papaverine has a separate effect on DNA synthesis, the reduced incorporation into DNA could be explained by its ability to increase the breakdown of intracellular thymidine phosphates.