Depression of ventilation by dopamine in goats--effects of carotid body excision.

Dopamine (DA) given IV by bolus injection (5, 10, 20 micrograms/kg) and by slow IV infusion (20 micrograms . kg . min) depressed VE significantly in awake normoxic goats. These responses were attenuated but not eliminated during hypoxia (FIO2 = 0.14) and hyperoxia (FIO2 = 1.0). After administering haloperidol (0.3 mg/kg) or removing the carotid bodies (CBE) there was greater attenuation of the response to DA. In normal goats haloperidol also caused a significant increase in ventilatory response to acute hypoxia and exaggerated depression of VE after 3--5 breaths O2 during steady-state hypoxia. After CBE haloperidol caused mild hypoventilation (delta PaCO2 = +2.5 Torr). CBE induced hypoventilation in goats (delta PaCO2 = +7.8 Torr) and reduced, but did not totally eliminate, peripheral chemoreceptor responses to acute stimuli (NaCN injection, transient N2 and transient O2 breathing). Attempted aortic body denervation did not eliminate these residual responses. We conclude: (1) DA may function as a modulator of carotid body (CB) function in the goat, (2) there may be central excitatory DA receptors in the goat, (3) the CB is important in regulating resting ventilation in the goat.