Effects of the dopamine antagonists haloperidol and domperidone on the normoxic ventilatory response to CO2 in cats.

We investigated the effects of the dopamine antagonists haloperidol and domperidone on the ventilatory response following square-wave changes in end-tidal CO2 during normoxia in chloralose-urethane anaesthetized cats. In 7 cats these responses were measured before (control, 28 runs) and after the administration of 1 mg/kg haloperidol i.v. (26 runs) and in 8 other cats before (39 runs) and after 0.5 mg/kg domperidone i.v. (34 runs). Each response was separated into a slow central and a fast peripheral part by fitting two exponential functions to the measured ventilation. These functions have as parameters a CO2 sensitivity, a time constant, a time delay and an apnoeic threshold B (extrapolated PETCO2 of the steady-state response curve at zero ventilation). Haloperidol significantly diminished the peripheral (Sp) and the central (Sc) ventilatory sensitivity to CO2 and the B-value (P less than 0.001). The ratio Sp/Sc, the time constants and the time delays were not significantly changed. Domperidone only diminished the B-value significantly (P less than 0.001). Since domperidone does not readily cross the blood-brain barrier, its effect was a CO2 independent increase of the ventilation mediated by the peripheral chemoreceptors. Haloperidol exhibited, besides the peripheral stimulatory effect a depressant central effect due to an action on the central integrative structures, resulting in a proportional decrease of Sp and Sc.