Respiratory and metabolic responses of the spiny rats Proechimys yonenagae and P. iheringi to CO2.

The recently described burrow-dwelling Proechimys yonenagae from the Brazilian semiarid caatinga was compared to P. iheringi from the Brazilian rain forest of Mata Atlântica in terms of interactions between body temperature (Tb), ventilation (VE) and oxygen consumption (V(O2)) during hypercapnia (5 or 10% CO2). Wistar rats were also used as a control. VE was measured by plethysmography, Tb by inserting a probe into the colon, and V(O2) by a close-flow system. During air breathing, VE did not differ between the rodents, Wistar Tb was elevated compared to P. yonenagae, and the V(O2) values of P. yonenagae and P. iheringi were significantly lower than those of Wistar rats. Hypercapnia caused hyperventilation in the three rodents, hypothermia in P. yonenage and Wistar rats, but no change in V(O2) was observed in any of the rodents. The hypercapnia-induced hyperventilation may be a major factor producing heat loss. This effect was independent of V(O2). Comparisons of the two spiny rat species suggest little adaptation of P. yonenagae to hypercapnia in burrows.