5-Hydroxytryptamine receptors. Contractile activity and mode of inhibition by methysergide in mammalian intracranial and extracranial vessels.

The contractile effect of 5-HT on intra- and extracranial arteries from rabbit, cat, dog and man and its interaction with methysergide was investigated. ED50 and EAm values for 5-HT from both types of arteries differed. Intracranial arteries stimulated by 5-HT were more sensitive to methysergide than extracranial arteries. In intracranial vessels the methysergide antagonism is non-competitive while in extracranial it is competitive. These differences might suggest a heterogeneity of 5-HT receptors located within the cranial circulation.