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 Atlantica in terms of interactions between body temperature (Tb), Ventilation ((V) over dot E) and oxygen consumption ((V) over dot (O2)) during hypercapnia (5 or 10% CO,). Wistar rats were also used as a control. (V) over dot E was measured by plethysmography, Tb by inserting a probe into the colon, and (V) over dot (O2) by a close-flow system. During air breathing, (V) over dot E did not differ between the rodents, Wistar Tb was elevated compared to P. yonenagae, and the (V) over dot (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) over dot (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) over dot (O2). Comparisons of the two spiny rat species suggest little adaptation of P. yonenagae to hypercapnia in burrows. (C) 1998 Elsevier Science B.V. All rights reserved.