| Abstract: | Hydroxyurea, when administered intraperitoneally as three consecutive and varying doses into 7-day-old rats, showed no inhibitory effect on thymidine kinase activity in the cerebral region of the brain. However, when injected intraperitoneally as a single dose into pregnant rats, the activity was found to be significantly inhibited in 16-day-old embryonic cerebrum. The inhibitory effect of the drug was time-dependent. The drug, however, showed no effect on thymidine kinase activity in vitro in either case. On the basis of these results along with our earlier observation regarding the action of hydroxyurea on thymidine kinase activity in 7-day-old cerebellum (1), we conclude that the inhibitory action of hydroxyurea on thymidine kinase activity is dependent on the proliferative stage of cells under study. We further speculate that there may be different forms of thymidine kinase in rapidly dividing and non-dividing cells. |
