Aminophylline may stimulate respiration in rats by activation of dopaminergic receptors

In intact young rats anesthetized with halothane, aminophylline produces an increase in respiratory minute ventilation due primarily to an increase in respiratory frequency. Although the simulation of respiration by inhalation of 10% CO2 is augmented only at high doses of aminophylline, the response to CO2 is increased at doses as low as 3 mg/kg of aminophylline. Division of the ninth cranial nerve together with removal of the carotid body did not alter the response, whereas vagotomy changed the response from one of increased frequency to an increase in tidal volume. Both awake and anesthetized rats evidence a decrease in PaCO2; after aminophylline administration and in awake animals, a decrease in brain stem dopamine content was observed. Since haloperidol, a dopamine antagonist, blocked the response to aminophylline, it seems likely that aminophylline may stimulate respiration by altering dopamine receptor activation in the brain.