The effect of exogenous dopamine on canine trachea

The response of canine trachea to exogenous dopamine was studied in vivo. Pentobarbital-anesthetized dogs were treated with dopamine through i.v. injection and i.v. infusion. The dopamine-induced constriction of the trachea was evaluated from changes in the intraluminal pressure of a semi-isolated section. The respiratory flow was monitored with a pneumotachograph. Dopamine administered through i.v. infusion (4-12 micrograms/kg/min) increased the blood pressure but decreased the respiratory rate and flow. At infusion rate of 8 micrograms/kg/min or higher, the intraluminal pressure went up gradually and recovered at the end of infusion. Bolus i.v., injection of dopamine (10-100 micrograms/kg) increased the blood pressure and the intraluminal pressure of trachea, but decreased the respiratory rate and flow. The pressure change in the tracheal tube lasted 2 to 3 minutes. These results demonstrate that, in addition to its well known effect on raising blood pressure, exogenous dopamine can induce transient constriction of the trachea in living animals. The constriction is accompanied by changes of respiratory pattern.