AJP - Regulatory, Integrative and Comparative Physiology, Vol 246, Issue 1 49-R55, Copyright © 1984 by American Physiological Society
CO2 balance of a heterothermic rodent: comparison of sleep, torpor, and awake states
P. E. Bickler
CO2 homeostasis of different thermal states have been compared in a
heterothermic ground squirrel, Spermophilus tereticaudus. Gas exchange
(MO2, MCO2), lung ventilation (VE), and body temperature (Tb) were
simultaneously measured during sleep, shallow torpor (Tb 25-29 degrees C),
deep torpor (Tb 11-15 degrees C), awake heterothermia (Tb 30-42.5 degrees
C), and transitions between these states. CO2 retention (falling MCO2/MO2
and VE/MCO2) accompanied entrance into sleep and torpor. CO2 retention
lowered MO2 in sleeping and torpid squirrels beyond that caused by reduced
Tb. In torpor at steady state, MCO2/MO2 (R) and ventilation returned to
control values, and no further CO2 retention occurred. Arousal from sleep
or torpor was accompanied by transiently high VE/MCO2 and R values as CO2
was released from the body fluids. R and VE/MCO2 values during
heterothermia in awake squirrels (Tb 32-42.5 degrees C) showed that total
body CO2 content remained unchanged until Tb reached 40 degrees C with
onset of hyperventilation. Altered CO2 content of the body fluids is thus
not a general feature of mammalian heterothermy. The difference in CO2
homeostasis of torpid and heterothermic awake animals may have implications
for the difference in metabolic intensity of these states.
