Potentiation and antagonism of serotonin effects on intracranial and extracranial vessels

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Abstract
The vasoconstrictor action of serotonin and its interaction with drugs (methysergide, pizotifen, cyproheptadine, ergotamine, dihydroergotamine) that have serotonin-antagonistic properties and that are used in the treatment of migraine were studied on isolated feline and human intracranial and extracranial arteries in vitro. The intracranial vessels were more sensitive to serotonin than the extracranial ones. The serotonin antagonists caused the expected impairment of the serotonin-induced contraction. In minute doses, the various compounds potentiated the contraction produced by serotonin. There is reason to believe that the mechanism responsible for this interaction is selective for tryptaminergic agents. This dual action of the serotonin antagonists may contribute to a beneficial effect in migraine by an interference during both the vasoconstrictory and vasodilatory phase.