Neutrophil chemoattractant production by cultured serotonin-stimulated bovine and human endothelial cells

Recent studies have demonstrated that serotonin (5-HT) is avidly taken up and metabolized by vascular endothelial cells (EC) and have suggested that 5-HT may contribute to inflammatory responses. Because EC can produce neutrophil cytokines among their biologically active molecules, we hypothesized that the interaction of 5-HT and EC might cause production of such a cytokine. Using a modified Boyden chamber assay, we found that cultured bovine aortic (BA), bovine pulmonary arterial (BPA), and human umbilical vein (HUV) EC incubated with 5-HT produced a neutrophil chemoattractant (NCA). The NCA was predominantly chemotactic, was not stored in an active form, appeared within 5 min of incubation with 5-HT, and required de novo protein synthesis for its appearance. The mechanism of NCA production was different in the three types of EC examined. Elaboration of NCA and BAEC and HUVEC was apparently mediated by 5-HT1 receptors and did not require uptake of 5-HT, whereas its elaboration from BPAEC required 5-HT uptake and was apparently mediated by 5-HT2 receptors. Incubation with three different lipoxygenase inhibitors blocked production of NCA, whereas incubation with a cyclooxygenase inhibitor did not. Further characterization of the NCA demonstrated that it was a mixture of several different chemotactic lipids and was distinct from other lipid or phospholipid neutrophil chemoattractants. These studies suggest that the interaction of the platelet-release product, 5-HT, with the adjacent endothelium results in the production of a chemoattractant that could affect neutrophil accumulation at sites of inflammation.