Ventilatory and metabolic responses to cold and CO-induced hypoxia in awake rats

Abstract

Experiments were carried out in awake rats to compare the effects of ambient and CO-induced hypoxia on thermoregulation and ventilatory control. Measurements of metabolic rate (V̇ O 2 ), ventilation (V̇), shivering (EMG) and colonic temperature (Tc) were made at fixed ambient temperature (Ta) of 25, 15 and 5°C. Animals were exposed to ambient hypoxia (F I O 2 of 21, 17, 14, 12 and 10%) or to CO hypoxia (F I CO of 0.03% in air). The results show that: (1) Both ambient and CO-induced hypoxia provoked decreases in V̇ O 2 and Tc which were more marked at low Ta values; non-shivering thermogenesis was depressed with both types of hypoxia, whereas shivering was depressed only with ambient hypoxia; (2) Ventilatory response to ambient hypoxia was blunted at low Ta values and CO-induced hypoxia did not affect ventilation. It is concluded that: (1) hypoxia affects markedly the control of Tc by altering thermogenesis: inhibition of non-shivering thermogenesis seems to result from a decrease in Ca O 2 whereas inhibition of shivering seems to result from a decrease in Pa O 2 ; (2) during hypoxia, ventilation is controlled by the opposite stimulation from chemoreceptors and inhibition from hypometabolism. However, as revealed by CO-induced hypoxia, another stimulatory factor may also interact with the control of breathing.