Effects of carotid body chemoreceptor stimulation by norepinephrine, epinephrine and tyramine on ventilation in the rabbit

Effects of norepinephrine, epinephrine and tyramine on the carotid body chemoreceptor in the rabbit were studied by measuring reflex ventilatory responses. The basic pattern of the responses was transient inhibition with a decrease in tidal volume followed by sustained excitation, even though the predominant feature was excitation in the epinephrine-induced response. The initial inhibition which was either unaffected or slightly potentiated after phenoxybenzamine was completely blocked by haloperidol. The late excitation was enhanced after mecamylamine and haloperidol treatments and was abolished following administration of phenoxybenzamine. The results indicated possible participation of inhibitory dopamine receptors for the induction of the initial depression and reduction of blood flow in the vessels of the carotid body by vasoconstriction for the excitatory response.