Cholinergic cerebral vasodilator effect of ketamine in rabbits.

To analyze the mechanism of the cerebral vasodilator effect of ketamine in anesthetized rabbits, we measured the internal carotid blood flow with an electromagnetic flowmeter, the arterial pressure, intracranial pressure, end-tidal CO2, and the electroencephalogram. Ketamine injection (1 mg/kg) induced a significant cerebral vasodilatation that was blocked by scopolamine, a cholinergic antagonist. In contrast, the increase in cerebral blood flow after ketamine was additive to the cerebral vasodilator actions of inhaled CO2 and of physostigmine infusion, two procedures that activate cholinergic mechanisms. These observations suggest that in rabbits, ketamine activates a cholinergic cerebral vasodilator system.