Effects of dopaminergic blockade upon carotid chemosensory activity and its hypoxia-induced excitation

The effects of domperidone, antagonist of D₂ receptors, on arterial chemoreceptor activity were studied in spontaneously breathing and pentobarbitone anesthetized cats, in which recordings of chemosensory impulse activity were obtained simultaneously from both cut carotid (sinus) nerves. Intravenous injections of domperidone 50 μg/kg produced a maintained increase in the basal frequency of chemosensory discharges, after which hyperoxic tests (breathing 100% O₂ for 30 s) evoked larger falls in the rate of chemosensory impulses. Chemosensory responses evoked by hypoxic hypoxia (100% N₂ tests) and by cytotoxic hypoxia (i.v. injections of NaCN) reached higher impulse rates after domperidone treatment. The effects of domperidone reveal that a resting release of dopamine from glomus cells maintains a low level of basal chemosensory activity under normoxic conditions. Domperidone turns off such restraining dopaminergic control and enhances the transient chemosensory responses to hypoxic stimuli. Present data support a modulatory role for dopamine within the chemoreceptor process, but not its participation as excitatory transmitter between glomus cells and sensory nerve endings.