Forearm vascular responses to serotonin are not mediated by products of cyclooxygenase

The involvement of cyclooxygenase-derived substances in the forearm arteriolar responses to serotonin was determined in 10 healthy male volunteers. Serotonin was infused in five incremental doses (0.003-30 micrograms min-1) for 2 min each into the brachial artery of the non-dominant forearm. Forearm blood flow (FBF) responses to each dose were measured by strain-gauge venous occlusion plethysmography. The cyclooxygenase inhibitor indomethacin (100 mg) was administered orally following the serotonin infusions. After 90 min the serotonin infusions were repeated and FBF responses measured. Serotonin caused a biphasic response with vasodilatation occurring at low doses (0.003-3 micrograms min-1, P < 0.01) and vasoconstriction occurring at the highest dose (P < 0.01). There was no significant difference in vascular response to serotonin following cyclooxygenase inhibition. In conclusion, cyclooxygenase products are not involved in the forearm vascular responses to serotonin in healthy human subjects.