ERYTHROPOIETIN AND ERYTHROID PROGENITORS IN RATS EXPOSED TO CHRONIC HYPOXIA

In order to better understand the mechanisms affecting erythropoietin (Epo) synthesis and red cell mass. increase under chronic hypoxia, we examined Epo production and erythroid progenitors (CFUE) in rats expos ed to normobaric hypoxia for four weeks. Hypoxia induced the rise of h ematocrit (Htc), hemoglobin (Hb) concentration and the red blood cell (RBC) number with a plateau in hematocrit values after two weeks. Afte r 24 h of hypoxia, Epo levels were increased 20 ford, followed by a si gnificant decrease. After the first week of hypoxia, the values were s till higher than in the controls, but after two weeks Epo levels did n ot differ significantly from the normal values. The fall of Epo levels coincided with the plateau values of hematocrit, The changes in the C FU-E number followed the changes in Epo concentration: a two fold incr ease after 24 h of hypoxia; a further increase during the next two wee ks reaching a peak on day 14, and then a progressive decrease at the t ime when Epo concentration was at a normal level. Although decreased, but still higher than normal, the CFU-E number during the last two wee ks of hypoxia could be necessary for the maintenance of an achieved st eady state under persistent hypoxic conditions with normal Epo concent ration sufficient to maintain the existing rate of erythropoiesis.