title: Determination of thymidine in serum used for cell culture media.
abstract: Thymidine concentrations in serum used for cell culture media were determined with an assay based on isotope dilution. In this assay, incorporation of (3H)-thymidine into  DNA of cultured cells was measured in the presence of 5 and 20% serum as a function of the concentration of unlabeled thymidine added to the medium. In three batches of horse serum, thymidine concentrations were 0--0.17 micron, while in fetal calf serum values of 0.75--2.1 micron were obtained. Dialysis of serum resulted in a reduction of thymidine levels by factors of at least 10.
mesh_terms: D002478:Cells, Cultured; D003470:Culture Media / Q000032:analysis*; D004247:DNA / Q000096:biosynthesis*; D011865:Radioisotope Dilution Technique; D013936:Thymidine / Q000032:analysis* / Q000378:metabolism
chemical_list: D003470:Culture Media; D004247:DNA; D013936:Thymidine