[Effect of long-term adaptation of rats to hypoxia on the proliferation of bone marrow erythroid cells. I. An increase in cell flows and a decrease in the duration of mitosis].

A 60 day adaptation of Wistar rats to hypoxia (six times a week, 6 hours a day) leads to: (1) the increase in cell flow from any phase of the erythroid cell life cycle to the next phase; (2) the change in the duration of the life cycle phases, corresponding to erythroblasts, basophilic normoblasts, and polychromatophilic normoblasts of the third type, (3) the shortening of the duration of all the mitotic phases by, in average, 1.8 times, and (4) the shortening of the radiation G2-block from 60 to 10 minutes. The changes in the mitotic index within a 24 hour period may be explained by non-periodic changes in the value of the cell flow from phase G2 to the mitosis every 6 hours, provided the duration of mitosis being constant. For cell populations with the daily rhythm of the mitotic index the calculation of the length of mitosis was made more exactly using the colchicine method.