[Central and peripheral mechanisms of hypotension induced by dl-propranolol in the dog]

The IV injection of 1-2 mg/kg dl-propranolol in dogs elicited a reduction of arterial blood pressure accompanied by a blockade of hypertensive responses to carotid occlusion or stimulation of the central trunk of the vagus. The same fall of blood pressure and identical blockades were seen following propranolol injected in the cisterna magna at a total dose of 2-5 mg. This late treatment also abolished the hypertensive response to KCl injected into the cisterna magna. On the other hand, propranolol failed to modify significantly responses to the electrical stimulation of hepatic and splenic sympathetic fibers and did not influence the hypertensive effects of adrenaline and noradrenaline. These findings are compatible with the notion that propranolol lowers systemic blood pressure via an action on central nervous system vasomotive centers.