Effect of acetylcholine and vasoactive intestinal peptide on cerebral blood flow

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Abstract
To determine whether the neurotransmitters acetylcholine (ACh) and vasoactive intestinal peptide (VIP) increase cerebral blood flow (CBF), dogs and rabbits were studied. In anesthetized dogs infusion of very large doses of ACh (500 .mu.g/min) into the carotid artery increased CBF (measured with microspheres) 50%. Anatomical limitations prevented adequate testing of cerebrovascular responses in dogs. In anesthetized rabbits infusion of ACh (10 .mu.g/min) into the carotid artery produced a 2-fold increase in CBF. Vessels in gray matter were more responsive than vessels in white matter. ACh did not alter cerebral O2 consumption, which indicates that the dilator effect of the drug is not an indirect effect mediated through an increase in metabolism. The vasodilator response to ACh was attenuated by atropine (1 mg i.v.). Intracarotid infusion of VIP in rabbits increased blood flow to cerebral gray matter; infusion of VIP (10 .mu.g/min) increased flow 33%. Cerebral vasodilator responses to ACh and VIP are larger than previously recognized. Responses to these drugs occur primarily in cerebral gray matter.