The transport of cytidine into rat brain in vivo, and its conversion into cytidine metabolites.

Double-labeled cytidine, with a 3H/14C isotope ratio of 20.00, has been intraventricularly injected into the brain of young rats, and its fate followed up to 90 min from administration together time-course of labeling. The injected nucleoside enters the brain as an intact molecule and is immediately utilized without prior degradation. Cytidine is actively converted into uridine and CMP, the latter being then transformed by a stepwise mechanism into CDP and CTP, and finally into CDP-choline and CDP-ethanolamine. The results indicate that administered cytidine represents a compound likely to enter metabolic events, which lead to CDP-choline and CDP-ethanolamine synthesis, and presumably to phospholipid production.