Effect of dehydration on erythropoiesis in mice: relevance to the "anemia" of space flight.

Mice deprived of water for 24 h showed an increase in hematocrit and loss of body weight comparable to that seen in men during space flight. The increase in hematocrit was entirely due to a decrease in plasma volume and was associated with suppression of erythropoiesis, but with no significant change in the serum titer of a presumptive humoral regulator of erythropoiesis, Erythroid Stimulating Activity (ESA). Mice deprived of water for 24 h may be a useful model for the study of the early hematological effects of space flight. The suppression of erythropoiesis due to a relative erythrocytosis appears to be independent of ESA.