Urinary Excretion of Deoxycytidine in Rats after X-irradiation: Dose-response and Effect of Age

Abstract

Rats were exposed to various doses of whole-body X-rays, from 10 R to 400 R, and 24-hr. urinary deoxycytidine (CdR) excretion was determined by combined ion exchange and paper chromatographic methods. The baseline 24-hr. urinary CdR excretion (non-irradiated rats) was 86.6 [plus or minus] 13.9 [mu]g; 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 1st 24 hr. after irradiation, and returned to baseline levels by the 2nd day. A linear dose-response relationship was found for 24-hr. 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-hr. urinary CdR content over that of non-irradiated age controls; for 12-week-old animals the increase was 123%; in 14-month-old rats, the increment was only 47%. The biochemical origin of the excreted CdR as a degradation product derived from the polydeoxyribo-nucleotides, 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.