Circulatory mechanisms underlying adaptive increases in thermogenic capacity in high-altitude deer mice.

We examined the circulatory mechanisms underlying adaptive increases in thermogenic capacity in deer mice () native to the cold hypoxic environment at high altitudes. Deer mice from high- and low-altitude populations were born and raised in captivity to adulthood, and then acclimated to normoxia or hypobaric hypoxia (simulating hypoxia at ∼4300 m). Thermogenic capacity [maximal O consumption (), during cold exposure] was measured in hypoxia, along with arterial O saturation (a ) and heart rate (). Hypoxia acclimation increased by a greater magnitude in highlanders than in lowlanders. Highlanders also had higher a  and extracted more O from the blood per heartbeat (O pulse=/). Hypoxia acclimation increased , O pulse and capillary density in the left ventricle of the heart. Our results suggest that adaptive increases in thermogenic capacity involve integrated functional changes across the O cascade that augment O circulation and extraction from the blood.