Potentiation of the cerebrovascular response to intra-arterial 5-hydroxytryptamine

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Abstract
Infusion of 5-hydroxytryptamine [serotonin] (5HT) into the internal carotid artery of normal baboons [Papio ursinus] was not accompanied by alteration of gray matter cerebral blood flow. In animals pretreated with depot estrogen and progesterone (dosage equivalent to oral contraceptive preparations), infusion of 5HT produced a marked decrease in gray matter blood flow. A similar decrease in flow was obtained when the 5HT was infused with a concentrate of .beta.-lipoprotein. Steroid substances appear to enhance the cerebrovascular constrictor responses to 5HT. A further series of 6 experiments has shown that the monoamine oxidase inhibitor tranylcypromine similarly produced constrictor responses to 5HT. It is possible that the steroids, the .beta.-lipoprotein and the tranylcypromine produced constrictor responses to 5HT by the same mechanism (inhibition of cerebrovascular monoamine oxidase). This data may be of use in understanding cerebral vasospasm.