Pressor response induced by local anaesthetics perfused through the cerebral ventricles of dogs.

1 The antihistamines mepyramine and halopyramine which have local anesthetic properties, produced a rise in arterial blood pressure followed by a fall, similar to that seen with procaine, when perfused in a 10 mg/ml solution from the lateral ventricle to the cisterna magna in dogs. 2 The pressor response produced by procaine perfused through the cerebral ventricle is due to an action on structures situated in the caudal half of the floor of the fourth ventricle because a pressor response was obtained when a few microlitres of a 50 mg/ml solution of procaine were applied to a small area of the exposed floor of the fourth ventricle in a region 2 to 4 mm rostral to obex, and after cauterization of this area procaine perfused through the cerebral ventricles no longer raised arterial blood pressure. 3 Bilateral denervation of the carotid sinus did not affect the pressor response obtained with procaine perfused through the cerebral ventricles. 4 The pressor response to procaine is mediated through the sympathetic nervous system. It results partly from an increased adrenaline discharge from the adrenal glands and partly from increased sympathetic vasomotor tone, because the response is abolished or attenuated after removal of the adrenal glands and intravenous injections of hexamethonium and phentolamine.