EFFECTS OF A CONTINUOUS-INFUSION OF DOPAMINE ON THE VENTILATORY AND CAROTID-BODY RESPONSES TO HYPOXIA IN CATS

1. We investigated how a continuous infusion of dopamine (DA; 5 mu g/k g per min), which is often used clinically, would affect the ventilati on and carotid chemoreceptor neural activity in anaesthetized cats. 2. In anaesthetized, spontaneously breathing cats, tidal volume (V-T) an d respiratory frequency (f) were continuously monitored at five levels of inspired oxygen (P-IO2 = 110, 130, 150, 170, 760 mmHg) during Da o r saline infusion. V-T and f were sampled for 1 min after 3 min exposu re to each level of P-IO2. Time control study was also performed. 3. D A infusion significantly lowered V-T under both normoxia and hypoxia i n seven of eight cats. Respiratory frequency was not affected by DA in fusion. Depression of ventilation during post-hypoxic hyperoxia was au gmented by DA infusion, Chemodenervation abolished the ventilatory res ponse to hypoxia and DA did not further affect the ventilatory respons e to hypoxia. 4. In a second group of artificially ventilated cats, ca rotid chemoreceptor neural activity was recorded at five levels of art erial oxygen tension. DA infusion significantly depressed carotid chem oreceptor neural activity during normoxia and hypoxia in six of seven cats. 5. These findings suggest that changes in ventilation during low dosage of DA infusion closely correlate with carotid body neural outp ut, A predominant effect of this dosage of DA (5 mu g/kg per min) was depression in the ventilatory response to hypoxia due to an inhibition of carotid body neural output.