Stimulation of carotid chemoreceptors and ventilation by doxapram in the cat.

Small doses of doxapram (less than 0.5 mg . kg-1 iv) were used to study its effect on carotid chemoreceptor activity and ventilation in cats anesthesized with alpha-chloralose. The effects were studied at several levels of partial pressures of O2 and CO2 in arterial blood (PaO2 and PaCO2). It was found that doxapram stimulated discharge rate of the carotid chemoreceptor afferents by the same magnitude at all levels of PaO2 and PaCO2 studied. However, the ventilatory effect of doxapram was more than additive to the concomitant stimulation by hypoxia or hypercapnia. This ventilatory effect was eliminated by sectioning the carotid sinus and aortic nerves. These results led to the conclusion that the ventilatory stimulus interaction due to doxapram is dependent on the excitatory input from the peripheral chemoreceptors.