Control of metabolic and ventilatory responses to cold in anesthetized cats

Abstract

Interactions between the control of thermogenesis and ventilation were studied during normoxia, hyperoxia, and ambient or CO hypoxia in adult anesthetized intact or carotid-denervated cats. Shivering, metabolic and ventilatory responses to cold stress were studied. In addition, the effects of transient pharmacological stimulation (NaCN) or inhibition (Dopamine) of arterial chemoreceptor activity were studied under different levels of oxygenation. In intact animals, cold exposure provoked increases in V̇ O2 and ventilation which were directly proportional to the intensity of shivering. During ambient or CO hypoxia, V̇ O2 was less than in normoxia for all values of shivering intensity, suggesting that a non-shivering thermogenesis component may also be inhibited by hypoxia. The decrease in V̇ O2 was associated with a smaller decrease in ventilation in ambient than in CO hypoxia because of the presence of the chemoreflex drive during ambient hypoxia. Pharmacological changes in chemoreceptor activity induced transient and opposite changes in ventilation and shivering intensity, confirming their role in the control of thermogenesis. After carotid denervation, when the drug effects were incosistent or absent, changes in levels of oxygenation were still followed by changes in shivering activity and associated changes in V̇ O2 and ventilation. We conclude that control of thermogenesis and ventilation and their interaction may be mediated by chemoreceptors as well as by direct effects upon central, possibly diencephalic structures.