Intracarotid administration of ionic contrast material and nicotine in conscious, unsedated dogs caused similar biphasic reflex responses consisting of initial decreases followed by increases in heart rate and pressures. Both phases were characterized by increases in respiratory amplitude. The initial hypotension was not observed when heart rate was maintained constant. The initial bradycardia was absent after denervation of the carotid body and cholinergic blockade. The tachycardia was attenuated after ligation of the internal carotid artery and beta adrenergic blockade. However, the hypertension persisted after denervation of the carotid body and ligation of the internal carotid artery but was attenuated after alpha adrenergic blockade. Nonionic contrast material caused almost no reflex hemodynamic effects.
Like noxious substances such as nicotine, ionic contrast materials cause complex hemodynamic effects as a consequence of actions on the cardiovascular centers of the brain, carotid body chemoreceptors, and chemosensitive tissue in the external carotid circulation.