BOILY, P.* P.; KNIGHT, F.M.: Cold-induced hyperthermia and maximum metabolic rate in the nine-banded armadillo

In response to cold temperature exposure, the nine-banded armadillo (Dasypus novemcinctus) undergoes an increase in metabolic rate concomitant with an increase in core temperature above thermoneutral values. This physiological response is incompatible with standard models of the control of body temperature in non-hibernating mammals where a negative feedback system inhibits heat production if core temperature rises above the setpoint. One possible explanation for this cold-induced hyperthermia is that resting armadillos are slightly torpid and that cold exposure causes the animals to arouse and increase their core temperature to a higher setpoint in order to increase metabolic heat production capacity. We tested this hypothesis by exposing armadillos to cold temperatures while simultaneously gas exchange rates (VO₂ and VCO₂) and core temperature at four locations (rectal 8cm and 16cm; esophageal 8cm and 16cm). Core temperatures were highly correlated to each other and changed during cold exposure according to the same pattern, thus indicating that cold-induced hyperthermia truly reflects a change in the internal heat content of the animal rather than a decrease in the size of the core. Peak VO₂ occurred approximately at the same time as peak core temperatures, thus supporting the hypothesis that cold-induced hyperthermia favors high metabolic rates. Peak VCO₂ often occurred well after the peak in core temperatures, when animals were hypothermic. This is likely the result of increased CO2 excretion resulting from the buffering of lactate by bicarbonates rather than an increase in the rate of CO₂ production. Funded by NSF (IBN-9723065 and ROA suppl.).