BOTH 5‐HYDROXYTRYPTAMINE 5‐HT2A AND 5‐HT1B RECEPTORS ARE INVOLVED IN THE VASOCONSTRICTOR RESPONSE TO 5‐HT IN THE HUMAN ISOLATED INTERNAL THORACIC ARTERY

Abstract

1. The 5-hydroxytryptamine (5-HT, serotonin) receptor subtypes that mediate vasoconstriction in the human internal thoracic artery (ITA), which is frequently used as an arterial graft, remain unclear. The aim of the present study was to elucidate the 5-HT receptor subtypes responsible for 5-HT-induced contraction of the human ITA. 2. The contractile responses to 5-HT of endothelium-denuded human ITA obtained from patients undergoing coronary bypass surgery were examined. In addition, we investigated the effects of sarpogrelate and SB224289, antagonists of 5-HT(2A) and 5-HT(1B) receptors, respectively, on the 5-HT-induced vasoconstriction. Finally, 5-HT(2A) and 5-HT(1B) receptors in the human ITA were immunolabelled. 3. 5-Hydroxytryptamine (1 nmol/L-10 micromol/L) caused vasoconstriction in a concentration-dependent manner. Both sarpogrelate (1 micromol/L) and SB224289 (1 micromol/L) significantly, but not completely, inhibited 5-HT-induced vasoconstriction. 4. Conversely, simultaneous pretreatment with supramaximum concentrations (1 micromol/L for both) of sarpogrelate and SB224289 almost completely inhibited the 5-HT-induced vasoconstriction. 5. Immunopositive staining for 5-HT(2A) and 5-HT(1B) receptors was detected in smooth muscle cells of the human ITA. 6. These results demonstrate that, in human ITA, 5-HT-induced vasoconstriction is mediated by activation of both 5-HT(2A) and 5-HT(1B) receptors. Thus, when the human ITA is used as an arterial graft, a combination of 5-HT(2A) and 5-HT(1B) receptor antagonists would appear to be most useful to prevent 5-HT-induced vasospasm.