Urinary excretion of deoxycytidine in rats after x-irradiation: dose-response and effect of age.

Abstract

SummaryRats were exposed to various doses of whole-body x-rays, from 10 R to 400 R, and 24-hour urinary deoxycytidine (CdR) excretion was determined by combined ion exchange and paper chromatographic methods. The baseline 24-hour urinary CdR excretion (non-irradiated rats) was 86·6 ± 13·9 μg; while after exposure to 28 R and 223 R, a significant increase of 70 per cent and 260 per cent, respectively, was observed. The highest rate of CdR excretion occurred during the first 24 hours after irradiation, 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 per cent 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 per cent increase in 24-hour urinary CdR content over that of non-irradiated age controls; for 12-week-old animals the increase was 123 per cent; in 14-month-old rats, the increment was only 47 per cent. 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.