In vivo analysis of cellular replication.

The number of previous cell replications that a metaphase cell has undergone in the presence of BrdUrd can be determined by the differential fluorescent patterns of metaphse chromosomes stained with Hoechst dye 33258. To examine if this technique could be applied to analyzing cell cycle kinetics in vivo, we infused Wistar rats with BrdUrd for 7.5-33 hr at concentrations of the nucleotide analog that did not inhibit cellular replication. Examination of the frequency of one, two, and three or more replication cycle cells as a function of BrdUrd infusion time indicates that cell replication times for rat bone marrow cells are relatively homogeneous. Analysis of this data with a computer simulation model produced a mean cell cycle duration of 9.2 hr, which is compatible with the fastest times obtained with radioisotope studies. These results support the potential of nonradioisotope analysis of cell replication in vivo.