Regulation of breathing and body temperature of a burrowing rodent during hypoxic?hypercapnia

Abstract

Burrowing mammals usually have low respiratory sensitivity to hypoxia and hypercapnia. However, the interaction between ventilation (V), metabolism and body temperature (Tb) during hypoxic–hypercapnia has never been addressed. We tested the hypothesis that Clyomys bishopi, a burrowing rodent of the Brazilian cerrado, shows a small ventilatory response to hypoxic–hypercapnia, accompanied by a marked drop in Tb and metabolism. V, Tb and O2 consumption (V̇O2) of C. bishopi were measured during exposure to air, hypoxia (10% and 7% O2), hypercapnia (3% and 5% CO2) and hypoxic–hypercapnia (10% O2+ 3% CO2). Hypoxia of 7% but not 10%, caused a significant increase in V, and a significant drop in Tb. Both hypoxic levels decreased V̇O2 and 7% O2 significantly increased V/V̇O2. Hypercapnia of 5%, but not 3%, elicited a significant increase in V, although no significant change in Tb, V̇O2 or V/V̇O2 was detected. A combination of 10% O2 and 3% CO2 had minor effects on V and Tb, while V̇O2 decreased and V/V̇O2 tended to increase. We conclude that C. bishopi has a low sensitivity not only to hypoxia and hypercapnia, but also to hypoxic–hypercapnia, manifested by a biphasic ventilatory response, a drop in metabolism and a tendency to increase V/V̇O2. The effect of hypoxic–hypercapnia was the summation of the hypoxia and hypercapnia effects, with respiratory responses tending to have hypercapnic patterns while metabolic responses, hypoxic patterns.