Meeting Abstract
Deer mice (Peromyscus manipulates) typically increase hematocrit during acclimation to high altitude in response to low oxygen tensions. When returning to low altitude, however, excess erythrocytes are unnecessary and costly due to increased viscosity that can increase the cost of circulation. Humans moving from high to low altitude have been shown to shunt excess erythrocytes from the circulating blood to the spleen causing an increased spleen size at low altitude. To determine if this is occurring in deer mice, we acclimated them to either low (390m) or high altitude (3800m) for 9 weeks (n=15 at each altitude). At the end of the acclimation period 8 mice from each altitude were moved to the reciprocal altitude for 48 hours to determine the effect of an abrupt change in oxygen availability on spleen mass and hematocrit. The remaining 7 mice were measured at the acclimation altitude. Spleen mass in the continuously high altitude mice was significantly smaller (28%) than in the continuously low altitude mice. However, hematocrit in the continuously high altitude mice was significantly higher (10%) than in the continuously low altitude group. There was no difference in hematocrit or spleen mass between continuously low altitude and high altitude mice that were moved to low altitude in the previous 48 hours but there was a significant negative correlation of r=0.77 between spleen mass and hematocrit in the high altitude mice moved to low altitude, suggesting that these mice had sequestered the excess erythrocytes in the spleen. Our results show that in addition to changes in lung and heart mass, deer mice possess another avenue of rapid phenotypic flexibility to maintain efficient oxygen delivery to tissues in variable oxygen tensions.
