VENTILATORY AND METABOLIC RESPONSES TO COLD AND CO-INDUCED HYPOXIA IN AWAKE RATS

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 (V-O2), ventilation (V), shivering (EMG) and colonic temperature (Tc) were made at fixed ambient temperature (Ta) of 25, 15 and 5 degrees C. Animals were exposed to ambient hypoxia (FIO2 of 21, 17, 14, 12 and 10%) or to CO hypoxia (FICO of 0.03%, in air). The results show that: (1) Both ambient and CO-induced hypoxia provoked decreases in V-O2 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-O2 whereas inhibition of shivering seems to result from a decrease in Pa-O2; (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.