Interaction between body temperature and ventilatory responses in the face of hypercapnia in three species of rodents

Author(s)

Renata Cristina Habenchus Barros

• Document type: Master's Dissertation
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 1998-08-14

Examining board members

Luiz Guilherme de Siqueira Branco; Jose Eduardo Pereira Wilken Bicudo; Anette Hoffmann

• Advisor: Luiz Guilherme de Siqueira Branco

Abstract

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 (VE) and oxygen consumption (VO2) during hypercapnia (5 or 10% CO2). Wistar rats were also used to assess the participation of the nitric oxide (NO) pathway in hypercapnia-induced hypothermia and hyperventilation. VE was measured by plethysmography, Tb by inserting a probe into the colon, and VO2 by a close-flow system. ln the Wistar rats, measurements were performed before and after NO synthase bocker Nω-nitro-L-arginine (L-NNA) injection (intraperitoneally) and after 5% CO2 inhalation. During air breathing, VE did not differ between the three rodents, Wistar Tb was elevated compared to P. yonenagae, and the VO2 values of P. yonenagae and P. iheringi were significantly lower than those of Wistar rats. Hypercapnia caused hyperventilation in the three species, hypothermia in P. yonenage and Wistar rats, but no change in VO2 was observed in any of the rodents. A significant drop in body temperature was measured after L-NNA (40 mg-kg-1), accompanied by a reduction in VO2. Hypercapnia had no effect on L-NNA-induced hypothermia and the ventilatory response to hypercapnia was not changed by L-NNA. Comparisons of the two spiny rat species suggest little adaptation of P. yonenagae to hypercapnia in burrows. The two responses elicited by hypercapnia, i.e., hyperventilation and hypothermia, do not share NO as a common mediator. However, the L-arginine-NO pathway participates, although in an unrelated way, in respiratory function and thermoregulation. (AU)