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Release of Thymidine from X-irradiated Spleen in the Rabbit as Determined by a New Bioassay¹

Departments of Medicine A and Experimental Therapeutics, Roswell Park Memorial Institute, New York State Department of Health, Buffalo, New York 14203, and Onco-hematology Unit, Department of Medicine, University Hospital, 1205 Geneva, Switzerland

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.

¹ Supported by Research Grants CA-5834 and CA-12585 from the NIH, USPHS, and by Grants 3.114.69 and 3.386.70 from the Fonds National Suisse de la Recherche Scientifique.

² Present Address: Centre d'Onco-hematologie, Hôpital Cantonal, 1205 Geneva, Switzerland.

Received 6/12/72. Accepted 9/13/72.