Effect of ketanserin on 5-hydroxytryptamine-induced constriction in isolated, perfused canine basilar arteries exposed to blood.

The blocking effect of ketanserin, a 5-hydroxytryptamine (5-HT)2 receptor antagonist, was examined on responses to intra-luminal 5-HT or potassium chloride (KCl) in isolated and perfused canine basilar arteries before and after extraluminal whole blood by means of the stainless-steel cannula inserting method. Four hours after the application of blood, the constriction to 5-HT was significantly enhanced, while that to KCl was significantly attenuated. The absolute value in the decrease of perfusion pressure for the 5-HT-induced constriction sensitive to ketanserin was much greater after the blood application than that before the application. It is suggested that the augmentation of cerebrovascular responses to 5-HT in the early stage immediately after subarachnoid haemorrhage (SAH) might be mediated by 5-HT2 receptors at least in part. This early constrictor mechanism may be implicated in the aetiology of the following late stage of cerebral vasospasm after SAH.