EFFECTS OF DOPAMINERGIC BLOCKADE UPON CAROTID CHEMOSENSORY ACTIVITY AND ITS HYPOXIA-INDUCED EXCITATION

The effects of domperidone, antagonist of D-2 receptors, on arterial c hemoreceptor activity were studied in spontaneously breathing and pent obarbitone anesthetized cats, in which recordings of chemosensory impu lse activity were obtained simultaneously from both cut carotid (sinus ) nerves. Intravenous injections of domperidone 50 mu g/kg produced a maintained increase in the basal frequency of chemosensory discharges, after which hyperoxic tests (breathing 100% O-2 for 30 s) evoked larg er falls in the rate of chemosensory impulses. Chemosensory responses evoked by hypoxic hypoxia (100% N-2 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 o f dopamine from glomus cells maintains a low level of basal chemosenso ry activity under normoxic conditions. Domperidone turns off such rest raining dopaminergic control and enhances the transient chemosensory r esponses to hypoxic stimuli. Present data support a modulatory role fo r dopamine within the chemoreceptor process, but not its participation as excitatory transmitter between glomus cells and sensory nerve endi ngs.