Release of Thymidine from X-irradiated Spleen in the Rabbit as Determined by a New Bioassay

Summary

Plasma collected from the spleen of rabbits 2 to 4 hr after selective splenic irradiation decreased from 75 to 95% the uptake of ¹²⁵I-labeled 5-iodo-2′-deoxyuridine by a suspension of bone marrow cells from untreated rabbits. The factor responsible for the decreased uptake was found to be dialyzable and, on paper chromatography in 4 different solvent systems, had the same R_F values as did thymidine. Serial dilutions of this factor gave a dose-related response in the bone marrow suspensions that was identical to that obtained with thymidine, 0.01 to 0.25 µg/ml, confirming the chromatographic identification of the plasma factor as thymidine. The extent of thymidine release as measured by this sensitive method may be useful in evaluating early cell damage following X-irradiation.