The distribution and fate of iododeoxycytidine (ICdR) and iododeoxyuridine (IUdR) have been compared. ICdR was more slowly degraded in the rat than IUdR. IUdR and iodouracil, but not iodocytosine, were identified as degradation products.

Following the administration of ICdR labeled with I131 or I125 to rats or mice, there was incorporation of the radioactive label in the DNA extracted from various organs. In the rat, concentration of radioactivity in the DNA of each organ was appreciably higher at 24 hours than at 1 hour after injection and was increased at the latter interval by pretreatment with 5-fluorodeoxyuridine.

Incorporation of ICdR into DNA of the rat was quantitatively less than that previously reported for bromodeoxycytidine (BCdR) and, except in the testis, less than that of IUdR. In the mouse the amounts of ICdR and IUdR incorporated into DNA were similar.

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Supported by grants CY-4096 and C 6135, National Institutes of Health, U.S. Public Health Service, Washington, D.C.

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