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Production of 5‐hydroxyindoleacetic acid from serotonin by cultured endothelial cells

Endothelial cells from bovine aorta and human umbilical vein and fibroblasts from human foreskin were cultured and subsequently evaluated for ability to metabolize serotonin (5‐HT) to 5‐hydroxyindoleacetic acid (5‐HIAA). Cells were incubated for three hours with 4 × 10−6 M [14C] 5‐HT creatinine sulfate. [14C] 5‐HIAA was separated from labeled 5‐HT by column chromatography and measured by scintillation counting. Production of 5‐HIAA by bovine aorta cells was 39.0 ± 7.5 (S.E.M., n = 6) nmoles per 109 cells per hour. Production of 5‐HIAA was markedly inhibited by the presence of 10−4 M iproniazid (an inhibitor of monoamine oxidase) or 10−4 M imipramine (an inhibitor of amine transport). 5‐HIAA was the only product of 5‐HT metabolism detected by thin layer chromatography. Production of 5‐HIAA by human umbilical vein endothelial cells was 5.4 ± 2.0 nmoles per 109 cells per hour (n = 5) and by human foreskin fibroblasts was 3.9 ± 1.4 nmoles per 109 cells per hour (n = 5). The results obtained during incubation in the presence and absence of inhibitors indicate that bovine aorta endothelial cells maintained in tissue culture are able to transport serotonin with subsequent production of 5‐HIAA. By contrast, human umbilical vein endothelial cells and fibroblasts exhibited relatively low rates of 5‐HT uptake and metabolism.