Blockade of alpha 2-adrenoceptors protects the vagal baroreflex system from transient global cerebral ischemia in dogs.

Ifenprodil, phentolamine, yohimbine or idazoxan, 1 mg/kg i.v., administered 5 min prior to 5-min global cerebral ischemia, completely prevented the post-ischemic dysfunction of the vagal baroreflex in anesthetized dogs. Idazoxan, 0.1 mg/kg i.v., was cerebroprotective against mild ischemia, but ineffective against severe ischemia. The post-ischemic administration of idazoxan, 1 mg/kg i.v., failed to restore the damaged vagal baroreflex. These results suggest that blockade of alpha 2-adrenoceptors during ischemia and the early reperfusion period may protect the vagal component of baroreflex from cerebral ischemia.