Intermittent exposure to hypobaria overcomes the suppressing effect of transfusion polycythemia on erythropoietin secretion.

Abstract

We have previously shown that transfusion polycythemia (TP) in mice suppresses erythropoietin (EPO) secretion in response to exposure to hypobaria when the hematocrit value is high enough. This effect, however, is not observed in mice with hypoxia-induced polycythemia (HP). In this condition, EPO secretion can be as high as that observed in normocythernic mice. Since HP was induced by intermittent exposure to hypobaric air, the present study was undertaken to explore the effect of daily exposures to hypobaria on EPO secretion in TP mice and rats, in which polycythemia was induced by two consecutive injections of packed homologous red cells. Animals were exposed continuously or intermittently (16 h/d) to hypobaric air in a decompression chamber. Blood was obtained at intervals and plasma immunoreactive EPO concentration (piEPO) determined by RLA. EPO values were taken as EPO production rates. TP blunted hypoxia-dependent EPO production during both continuous and the 3-4 first intermittent exposures. The suppressing effect of TP on EPO production decreased during the next intermittent exposures. These findings suggest that the mechanism controlling EPO gene transcription could be conditioned by intermittent exposure to hypobaria in such a way that makes it insensitive to the suppressing effect of polycythemia on hormone production.