Foetal haemopoiesis during the hepatic period. III. Erythroid cell kinetics.

Serial sections of haemopoietic liver from 12 to 17 days old mice embryos were studied. The percentual values of cycling erythroid cells, located at vascular level, show a continuous decay through the entire hepatic phase of erythropoiesis. Since the 15th day onwards no differences were found in the cellular blood composition between the general circulation and the vascular channels of the central area of the growing lobes. Nevertheless, other more peripheric areas of the liver have a slowed decrease of circulating young cells, when compared with the former. On the contrary, in the marginal zones, interstitial proerythroblasts increase their percentual values towards the 13th day, coinciding with the moment on which they predominate all over other more mature demes. This increment is not explainable by self renewal only, since their mitotic indexes undergo a decay, which is unexpected in a growing population. Interstitial non erythroid cells seem not to play a role in the increment of proerythroblasts in the proliferating areas.