URINARY EXCRETION OF DEOXYCYTIDINE: A POTENTIAL BIOCHEMICAL RADIATION DOSIMETER

Rats were exposed to various doses of whole-body X rays, from 10 R to 400 R, and 24-hour urinary deoxycytidine (CdR) excretion determined by combined ion exchange and paper chromatographic methods. The baseline 24-hour urinary CdR excretion (nonirradiated rats) was 86.6 plus or minus 13.9 Micrograms; while after exposure to 28 R and 223 R, a significant increase of 70% and 260%, respectively, was observed. The highest rate of CdR excretion occurred during the first 4 hours postirradiation, and returned to baseline levels by the second day. A linear dose-response relationship was found for 24-hour CdR excretion at radiation doses over the range of 10 R to 223 R. For a given radiation dose, CdR excretion was considerably lower in rats previously splenectomized; thus, at 100 R the spleen appeared to contribute 82% of the excreted CdR. Age of the rats was an important determinant of CdR excretion: after exposure to 100 R, 5-week old rats showed a 312% increase in 24-hour urinary CdR content over that of nonirradiated age controls; for 12-week old animals the increase was 123%; while in 14-month old rats, the increment was only 47%. The biochemical origin of the excreted CdR as a degradation product derived from the polydeoxyribonucleotides, previously shown to be released in spleen and thymus at early times after irradiation, is suggested. It is concluded that urinary CdR excretion may be potentially useful as a biochemical index of radiation exposure. (Author)