The nature of the pressor response to carotid artery occlusion in the hexamethonium-treated rat.

1. The blood pressure monitored from the cannulated right carotid artery and heart rate responses to occlusion of the intact left carotid artery were investigated in rats. 2. Hexamethonium abolished the response to ganglion stimulants but not that to carotid occlusion, although the time course and nature of the response were altered. 3. The pressor response to carotid occlusion in the presence of hexamethonium was not abolished by carotid sinus denervation, vagal section, tubocurarine, atropine, ethyl alcohol or an angiotensin II antagonist, but it was abolished by high doses of phenoxybenzamine. In six out of eight experiments the response was not abolished by cervical cord section. 4. It was concluded that the pressor response to carotid occlusion in the presence of hexamethonium in the rat involves an adrenergic mechanism which is at least in part independent of the autonomic ganglia, and which is mediated by an agent liberated from the brain, possibly under conditions of cerebral ischaemia.