Autonomic reflexes and the cardiovascular effects of propylene glycol

The effect of i.v. propylene glycol in doses of 160-800 mg kg-1 on heart rate, arterial pressure and efferent sympathetic activity were observed in anaesthetized paralysed, artificially ventilated dogs. Within 3-5 s of the commencement of the injection of propylene glycol there was an immediate mean decrease in heart rate of 22.7 and 72.1 beat min-1 and in arterial pressure of 27.2 and 58.8 mm Hg at doses of 400 mg kg-1 and 800 mg kg-1, respectively, together with a gross reduction of sympathetic activity and a subsequent increase in heart rate above control values. All these effects were transient and at a dose of propylene glycol 800 mg kg-1, heart rate and arterial pressure returned to control values by 1 min, and sympathetic activity by 2 min. Blocking the vagus nerves with atropine prevented the observed changes in heart rate and arterial pressure, whereas sympathetic blockade with bretylium tosylate had little effect. It was concluded that propylene glycol causes powerful reflex stimulation of the cardiomotor vagus and transient inhibition of efferent sympathetic activity within 5 s of injection, and that the origin of the reflex is likely to be intrathoracic.