Radioimmunoassays of plasma thymidine, uridine, deoxyuridine, and cytidine/deoxycytidine

Abstract

Radioimmunoassay techniques have been developed for the assay of thymidine, uridine, deoxyuridine, and deoxycytidine. Plasma levels of the first three nucleosides have been measured, and an upper limit has been determined for the plasma concentration of deoxycytidine. The assays involve displacement of a [ 3H]pyrimidine nucleoside from the appropriate labeled rabbit immunoglobulin. By assaying a mixture of uridine and deoxyuridine in the presence and absence of borax, the concentrations of both nucleosides have been measured. In seven healthy adults, plasma levels of uridine were 21.1 ± 8.4 μ m (mean ± SD) and of deoxyuridine were 0.62 ± 0.39 μ m. In cancer patients, thymidine levels were 7.5 ± 2.7 × 10 −7 m. The upper limit for plasma deoxycytidine levels in six healthy adults was 0.71 ± 0.1 μ m.