Haematological acclimation and re-acclimation to hypoxia in the mouse

•The haematological responses to initial acclimation (IA) and of re-acclimation (RA) to hypoxia were studied in mice.•The serum [EPO] response was blunted in all RA groups compared to IA but the resulting reticulocyte response was similar in all experimental groups.•Erythropoietic regulation is altered during RA in a manner that is dependent on the paradigm of initial exposure.

Haematological responses throughout 4 w of initial acclimation (IA) and three paradigms of re-acclimation (RA) to hypoxia (FIO2=0.12) were examined in female mice. We hypothesised that (i) haematological responses would be increased during re-exposure, resulting in greater O2-carrying capacity in RA compared to IA; and (ii) further improvements would occur when abbreviating the de-acclimation period to 1 w (RA↓DA) or extending the IA period to 8 w (RA↑IA). The serum [EPO] response was blunted in all RA groups compared to IA but the resulting reticulocyte response was similar in all experimental groups. The [Hb] response was the same in RA and RA↓DA as in IA but was blunted in RA↑IA due to a reduction in mean corpuscular Hb. The sensitivity of EPO-producing cells appears blunted but the sensitivity of erythroid precursors to EPO is enhanced by recent hypoxic exposure. Erythropoietic regulation is altered during RA in a manner that is dependent on the paradigm of initial exposure.