Fluctuations of BFUe and CFUe cycling after erytrhoid perturbations: correlation with variations of pool size.

The pool size of erythroid burst-(BFUe) and colony-forming units (CFUe) has been evaluated in normal or hypoxia-induced polycythemic mice at sequential times after either transfusion or administration of purified erythropoietin (Ep). The present investigations were focused on the in vitro tritiated thymidine (3H-TdR) suicide index of the erythroid precursors in these two experimental models. After transfusion an early but transient decline of the DNA sythesis index was observed in the BFUe pool, whereas this parameter showed a later, more prolonged decrease within the CFUe population. Symmetric patterns were documented after Ep injection: an early, transient elevation of the 3H-TdR sensitivity at the BFUe level and a late, more persistent rise within the CFUe compartment. In all experiments no modification of this indes was observed within the pool of the CFUe. These fluctuations of BFUe and CFUe cycling were temporally consistent with modifications of their respective pool size, as previously reported. Thus, variations of the pool size may be at least partially mediated by the cycling activity. Furthermore, early fluctuations of BFUe proliferative rate indicate that, after erythroid perturbations, this pool may initially be sensitive to and regulated by modifications of Ep activity. Later, however, compensatory mechanisms allow the BFUe to escape from this early Ep influence, thus leading its cycling activity and pool size to return to normality and stabilize.