Respiratory effects of dopamine-induced inhibition of chemosensory inflow.

In pentobarbitone-anesthetized cats, intracarotid injections of dopamin (DA) 0.05--20 micrograms produced transient ventilatory depression, enhanced by section of the contralateral carotid nerve and abolished by section of the ipsilateral one. I.v. injections of DA 0.02--2 micrograms-kg-1 also induced transient hypoventilation; this effect was abolished by bilateral section of the carotid nerves. Slow i.v. infusion of DA 10 micrograms-kg-1-min-1 elicited initially a pronounced hypoventilation followed by a steady-state of mild ventilatory depression; these changes were absent after bilateral carotid neurotomy. Recordings from carotid nerves showed that DA-induced decreases of chemosensory activity to 50% of its control did not modify ventilation, while chemosensory arrests transiently depressed ventilation to 40--75% of its control level. Interactions between the ventilatory and chemosensory depressant effects of hypertoxia and DA administration were also studied. It is proposed that the reflex decrease in ventilation caused by DA injections provides a measure of the tonic chemosensory drive exerted upon the respiratory center.