Tumour cell recruitment of the JB-1 and L 1210 ascites tumour determined directly by double labelling with [14C]- and [3H]-thymidine.

Tumour cell recruitment of the JB-1 and L 1210 ascites tumour has been demonstrated directly by a double-labelling method with [14C]- and [3H]-thymidine (TdR). After [14C]-labelling of all proliferating tumour cells by multiple injections of [14C]TdR, recruitment of resting cells was stimulated by removal of the majority of tumour cells, i.e. by maximum aspiration of ascitic fluid. The number of recruited resting cells in the remaining tumour that re-enter the cell cycle after stimulation was demonstrated directly by a single injection of [3H]TdR given at different times after stimulation. The increase in the percentage of purely [3H]-labelled cells, i.e. recruited cells, with increasing time after stimulation, shows that recruitment is not a synchronous but a continuous process, the maximum of which occurs earlier in the case of the L 1210 than the JB-1 tumour. This suggests that there seems to be a relationship between the time required for maximum recruitment and the corresponding cell cycle parameters of the unperturbed tumour. There is a transitory increase of the growth fraction to about 100% and a considerable shortening of the cycle time at the maximum of recruitment.