VASCULAR TONE AND REACTIVITY TO SEROTONIN IN INTERNAL AND EXTERNAL CAROTID VASCULAR BEDS OF DOG

Abstract

The effects of intr-arterial infusions of serotonin on internal and external carotid blood flow were determined in anesthetized dogs by electromagnetic flow measurements. Serotonin decreased flow in the internal carotid and increased it in the external carotid. Both responses were blocked by the serotonin antagonist, methysergide. The .alpha. adrenergic antagonist, zolertine, the ganglionic blocking agent, chlorisodamine and the vasodilator, diazoxide, blocked external carotid dilator responses but did not modify constriction in the internal carotid. Blockade of external carotid responses by the 3 drugs was demonstrated in experiments in which this bed was perfused at a constant rate. The internal and external carotid vascular beds of the dog probably react in opposite ways to serotonin, both responses being mediated through the same type of serotonin receptors, the dilator responses of the external carotid are probably dependent on vascular tone.