Cyclic fluctuation in blood granulocyte DNA labeling: comparison of tritiated thymidine and radiophosphorus.

DNA labeling studies with 3HT and 32P 27 hr. Simultaneous labeling studies have been done in horses. Frequent in the same animals have produced sampling has defined cyclic fluctuablood granulocyte DNA labeling curves tions in blood granulocyte DNA label that are nearly identical indicating content with a cycle time of around significant reutilization of 3HT. F LUCTUATION IN THE PERCENT OF LABELED CELLS in the blood of dogs after a single injection of tritiated thymidine (3HT) has been reported by Patt and Maloney,’ and Fliedner et al.2 have reported that a single injection of 3HT in man is followed by fluctuations in blood granulocyte DNA label concentration as indicated by radioautographic measurements of grain counts. The fluctuations, apparent only after maximum labeling was achieved, were visible in the labeling index for all labeled cells and also in the labeling index for classes of cells defined by any particular range of grain counts. Fluctuations of blood granulocyte DNA label concentration have also been observed in orthoradiophosphate (32P) labeling studies of rabbits.3 Assessment of detailed changes in blood granulocyte DNA label content requires sampling at intervals as short as feasible with as little perturbation of the system as possible. To accomplish this studies were done in the horse, an animal from which blood can be obtained relatively easily and in which perturbations due to the volume of blood removed for sampling should be minimal. Fluctuations in blood leukocyte DNA label concentration which were cyclic were demonstrated both with tritiated thymidine and orthoradiophosphate. Tritiated thymidine has been considered to represent a pulse or flash label with an availability of less than an hour4 while it has been shown that 32P as orthophosphate is available in significant concentration for several days after a single intravenous injection.5 These studies compare leukocyte labeling with 3HT and 32P simultaneously in the same animal to eliminate all variables other than the labeling characteristics of these two sub-