5-Hydroxytryptamine induces contraction in isolated human mammary artery: effect of ketanserin

5-hydroxytryptamine (5HT) treatment produced dose-related contractions in the human internal mammary artery with an EC50 value of 3.4 X 10(-7) M. The 5HT2 receptor antagonist ketanserin reversed the contractions evoked by 5HT in a competitive manner at a low concentration (10(-8) M), whereas a noncompetitive antagonism was apparent at higher concentrations (5 X 10(-8) M to 5 X 10(-7) M). The alpha 1-blocking component of ketanserin was evaluated by studying the effect of ketanserin upon the contractile response evoked by norepinephrine. Up to 10(-7) M, ketanserin did not influence norepinephrine-induced contractions. These findings indicate that the mammary artery is a vascular tissue sensitive to contractions induced by 5HT and that the drug ketanserin antagonizes this contractile response through the 5HT2 receptor subtype.