Effects of endotoxin on tryptophan metabolism in pigs

Background Inflammatory processes are associated with depletion of the essential amino acid tryptophan, the precursor of serotonin (5-HT). We evaluated the peripheral responses of tryptophan and both peripheral and brain metabolism of 5-HT to intravenous lipopolysaccharide (LPS) administration in pigs. Methods In 6 crossbread barrows Escherichia Coli LPS was infused. Six pigs served as controls. Arterial and cerebrovenous levels of plasma tryptophan, 5-hydroxyindoleaetic acid (5-HIAA) and platelet 5-HT were assessed 4, 24 and 120 h after infusion. Results In LPS treated pigs plasma tryptophan levels were depleted 4 and 24 h after infusion with no arterial-venous differences. 5-HT levels were enhanced in LPS exposed pigs with again no arteriovenous differences. Venous 5-HIAA levels were enhanced compared to arterial levels 120 h after LPS infusion. Plasma tryptophan levels correlated positively with with 5-HIAA levels 4 h after infusion in the LPS group. Discussion Following LPS there is an increased metabolism of peripheral and brain 5-HT.