A lipopolysaccharide and concanavalin A induce variations of serotonin levels in mouse tissues

The administration of an Escherichia coli lipopolysaccharide (LPS), or an endotoxin into mice produced a variation in tissue serotonin (5HT) levels within 4.5 h. 5HT levels in the kidney and lung were decreased by the higher doses of LPS, but those in the liver and spleen were increased even by lower doses of the agent. The increase in liver 5HT was most marked. Such variations in 5HT levels were also produced by the administration of concanavalin A. In vitro experiments using extracts from livers of LPS-treated and non-treated mice indicated that there was no difference in the 5HT formation from 5-hydroxytryptophan between the two groups, but that 5HT formation from tryptophan was higher in the LPS-treated mice. The LPS-induced 5HT increase in liver was suppressed by p-chlorophenylalanine (an inhibitor of tryptophan hydroxylase), actinomycin D, cycloheximide and dexamethasone, but not by Ro 4-4602 (an inhibitor of aromatic amino acid decarboxylase), pargyline (an inhibitor of monoamine oxidase) and indomethacin. A possible mechanism of the 5HT increase in the liver is discussed on the basis of these results.