ABSTRACT-5-Hydroxytryptamine(5-HT)-receptor subtypes on pig basilar arteries were investigated by measuring the contractile responses to 5-HT agonists, the effects of antagonists on the responses and by carry ing out a radioligand binding assay with [3H]5-HT. The rank order of contractile agonist potency (accord ing to the pEC50 values) was 5-carboxamidotryptamineThe contractile responses were not affected by endothelial denudation, and the 5-HT induced contractions were antagonized competitively by ketanserin. Methiothepin shifted the 5-HT concen tration-response curves to the right and downwards in a concentration-dependent manner. In the presence of ketanserin (10-6 M), however, methiothepin antagonized the 5-HT-induced contractions competitively.

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