AUTONOMIC REFLEXES AND THE CARDIOVASCULAR EFFECTS OF PROPYLENE GLYCOL

The effect of i.v. propylene glycol in doses of 160–800mg kg^–1. on heart rate, arterial pressure and efferentsympathetic activity were observed in anaesthetized paralysed,artificially ventilated dogs. Within 3–5 s of the commencementof the injection of propylene glycol there was an immediatemean decrease in heart rate of 22.7 and 72.1 beat min^–1and in arterial pressure of 27.2 and 58.8 mm Hg at doses of400 mg kg^–1 and 800 mg kg^–1, respectively, togetherwith a gross reduction of sympathetic activity and a subsequentincrease in heart rate above control values. All these effectswere transient and at a dose of propylene glycol 800 mg kg^–1,heart rate and arterial pressure returned to control valuesby 1 min, and sympathetic activity by 2 min. Blocking the vagusnerves with atropine prevented the observed changes in heartrate and arterial pressure, whereas sympathetic blockade withbretylium tosylate had little effect. It was concluded thatpropylene glycol causes powerful reflex stimulation of the cardiomotorvagus and transient inhibition of efferent sympathetic activitywithin 5 s of injection, and that the origin of the reflex islikely to be intrathoracic.