The inhibitory effect of theophylline on the incorporation of 3H-deoxycytidine and 3H-thymidine into thymocyte DNA.

In short term cultures of rat thymic lymphocytes, theophylline caused an early inhibition of incorporation of 3-H deoxycytidine into DNA without influencing the incorporation of 3-H-thymidine. Over a 4-hr incubation period, the inhibitory effect of theophylline on 3-H-deoxycytidine uptake into DNA remained at approximately 40%, while the suppression of 3-H-thymidine uptake increased to 20%. The results indicate that since there is a difference in the effect of the ophylline on the incorporation of 3-H-deoxycytidine and 3-H-thymidine into the DNA of thymus lymphocytes, inhibition of uptake of these deoxynucleosides by theophylline does not necessarily reflect inhibition of DNA synthesis or cell turnover.