Effect Of Polycythemia Research Articles

Effect of polycythemia on erythropoietin production in the hypoxic rat.

Effect of polycythemia on erythropoietin production in the hypoxic rat.

Effects of polycythemia and altitude hypoxia on rat heart and exercise tolerance.

Effects of polycythemia and altitude hypoxia on rat heart and exercise tolerance.

Hemopoietic spleen colony studies. II. Erythropoiesis.

The polycythemic repression of erythropoiesis and the restoration of erythropoiesis by specific stimulation were studied in the spleen colony system in irradiated mice. 1. A 5 day period of erythropoietin stimulation (exogenous erythropoietin) or repression (polycythemia) of the bone marrow donor only, does not significantly alter the number or type of colonies formed by the transplanted marrow cells. 2. Erythropoietin stimulation did not alter the number or type of endogenous colonies formed in mice receiving 580 R. Erythropoietin repression (polycythemia) markedly reduced the growth but not the number of erythroid colonies, while not affecting the other types of colonies formed endogenously. 3. Erythropoietin stimulation of the irradiated recipient during colony growth did not alter the number or type of spleen colonies formed by transplanted marrow. Erythropoietin repression by polycythemia during colony growth completely suppressed the appearance of morphologically erythroid colonies without significantly altering the incidence of the other colony types. This effect of polycythemia was completely prevented by exogenous erythropoietin. Irradiated mice are therefore presumed to be secreting sufficient erythropoietin for maximal erythroid colony development. 4. The erythroid colonies suppressed by polycythemia were recognizable as microscopic foci of undifferentiated cells. Exposure of these foci to erythropoietin stimulation at different periods in their development was manifested by different degrees of growth and differentiation, from which it is apparent that erythropoietin stimulates not only morphological differentiation but also rapid mitosis. Retransplantation of either erythroid or of neutrophilic primary spleen colonies gave rise to both erythroid and neutrophilic secondary spleen colonies. The percentage of erythroid secondary colonies was slightly but significantly higher among the progeny of transplanted erythroid primary colonies than among the progeny of transplanted neutrophilic primary colonies. On the basis of these and other results, a working hypothesis is proposed for factors controlling the growth and differentiation of spleen colonies from transplanted bone marrow. It is postulated that most but perhaps not all spleen colony-forming units are pluripotent hemopoietic stem cells. It is further postulated that hemopoietic-inductive microenvironments (HIM) of different kinds exist in both the spleen and the bone marrow, and that these determine the differentiation of pluripotent stem cells into each of the lines of hemopoietic differentiation. Erythropoietin therefore may "induce" erythroid differentiation of only those stem cells under the influence of an erythroid HIM. Alternatively erythropoietin may act only as a growth and function stimulant of those stem cells that have been "induced" by an erythroid HIM into a state of erythropoietin responsiveness. In the latter case morphological differentiation presumably results from the functional activity stimulated by ESF.

Studies on the Regulation of Hemopoietic Spleen Colonies

Abstract The in vivo intrasplenic cloning of haemopoietic cells was used as an experimental system for the study of some aspects concerned with the regulation of erythropoiesis. Experiments on the effects of polycythemia on the formation of erythroid clones demonstrated that the "feedback" suppression of such clones was inhibited if the polycythemic animals were kept under hypoxic conditions. Overloading with oxygen is, thus, an essential factor in the polycythemia-induced suppression of erythroid clones. Polycythemic animals which were transferred to hypoxic conditions for only 48 hours before the termination of the experiment showed the formation of erythroid clones. Analysis of clone formation following such short exposures to hypoxia suggests that the endogenous erythropoietin which had been functioning in this situation acted not upon the single clone-forming cell, but rather on small cell populations which derived from the clone-forming cells in the absence of erythropoietin. There is, therefore, an early, erythropoietin-independent phase of replication of the clone-forming cells. The application of erythopoietin only during this "early" phase of replication resulted in the formation of erythroid clones, which, following the discontinuation of erythropoietin, disappeared from the spleen. Similar results were obtained when the action of endogenous erythropoietin was terminated by subjecting animals to polycythemic conditions a few days after the injection of bone marrow. It appears that in both these cases the reduction in the number of spleen colonies following discontinuation of erythropoietin activity is due to the total maturation of the erythroid colonies, ending in the evacuation from the spleen of the mature red blood cells. The differentiation of the cloned cells is, thus, causally related to the cessation of the replicating effect of erythropoietin.

Effect of polycythemia and chronic hypoxia on heart mass in the chicken.

Effect of polycythemia and chronic hypoxia on heart mass in the chicken.

Effects of polycythemia and anemia on cardiac output and other circulatory factors

Normovolemic anemia and polycythemia were studied in 14 dogs. Cardiac outputs increased with anemia and fell with rises in hematocrit. Although many factors—such as chemical changes—may play an important role in these variations in cardiac output, there was an indication that viscosity alone may have a major effect. There was no significant association between changes in cardiac output and the various pressures—mean arterial, mean right atrial, mean pulmonary and mean circulatory. Although the pressures did not change significantly, there was a significant decrease in total peripheral resistance in anemia and a marked rise in polycythemia. It was also found that the maximum number of red cells present for oxygen transport to the tissues was near the mean normal hematocrit of 40.