Endogenous thromboxane A2 does not contribute to the contractile response of human umbilical artery strips to 5-hydroxytryptamine

Abstract 1. 1. To investigate the possible role of endogenous thromboxane A 2 (TXA 2 ) in 5-hydroxytryptamine (5-HT)-induced contraction, human umbilical artery strips were suspended in isolated organ chambers for measurement of isometric force. 2. 2. In endothelium intact strips, arachidonic acid (AA;1 μM) potentiates the contractile response to 5-HT, whereas the response was reduced by indomethacin (INDO;10 μM). De-endothelialized strips showed reduced responses to 5-HT. 3. 3. Arachidonic acid-induced potentiation of the responses to 5-HT was prevented by INDO, and the TXA 2 synthase inhibitor dazoxiben (DAZ;1 μM and 10 μM) was without effect on the responses to 5-HT in endothelium intact strips. 4. 4. Taken collectively, these results suggest that, in human umbilical artery strips, the contractile response to 5-HT is at least partly dependent on the 5-HT-induced release of an endothelium-derived contracting factor (EDCF), which is a cyclooxygenase metabolite. The lack of effect of DAZ indicates that TXA 2 is not the EDCF released during the contractile response of human umbilical artery strips to 5-HT.