Plasma levels of 5-HT and 5-HIAA increased after intestinal ischemia/reperfusion in rats

Abstract

Intestinal ischemia/reperfusion (I/R) causes serious systemic injury, mainly from a variety of bioactive substances released from the injured intestine. To assess the possible roles of serotonin (5-hydroxytryptamine, 5- HT), a bioactire amine mainly stored in the intestine, in I/R injury, we assayed the levels of tryptophan, 5HT, and 5-hydroxyindole acetic acid (5- HIAA) in the blood and intestine in a rat I/R model. Plasma 5-HT increased significantly over time after reperfusion; the plateau level was obtained 4h after reperfusion and was associated with an increase in 5-HIAA. Plasma tryptophan levels declined gradually after reperfusion. The ratio of 5- HIAA/5-HT was significantly higher in I/R rats than in control rats, suggesting that elevated 5HT was quickly metabolized in the systemic circulation. In the intestine, 5-HT decreased dramatically, whereas tryptophan increased. This phenomenon was prominent in the severely damaged intestine. These findings suggest that the injured intestine released large amounts of 5HT, whereas its synthesis in the injured intestine was suppressed. An increase in 5-HT in the circulation may be related to various circulatory disturbances observed in humans after intestinal ischemia.