Changes of tryptophan metabolism in Japanese runners during an ultra-marathon race

Abstract

Purpose: Under the assumption that tryptophan (TRP) metabolism may be modulated by the intensity, duration, and total exercise/energy expenditure of the ultra-marathon, we evaluated the changes in two major TRP metabolic pathway substances [serotonin (5-HT) and kynurenine (KYN)] during a two-day ultra-marathon race. Methods: Blood was sampled at three different time points: before the race (baseline), after running 45 km on the first day, and after running 135 km on the second day. Results: Serum TRP concentrations decreased in proportion to the distance covered, and the levels after running 135 km were significantly lower than at baseline and after running 45 km. Serum serotonin (5-HT) concentrations increased significantly after running 45 km but reduced towards baseline levels after running 135 km. Serum kynurenine (KYN) concentrations hardly changed after running 45 km but increased significantly after running 135 km compared with after running 45 km values. Serum FFAs levels increased significantly after running 45 km compared with baseline values, and they elevated even further after running 135 km. Serum albumin concentrations reduced significantly after running 45 km but remained at almost the same level after running 135 km. Serum 5-HT levels tended to be consistently correlated to the completion times on the first and second days. Conclusions: Serum 5-HT concentrations are known to be associated with central fatigue, and may predict exercise performance. KYN levels appeared to reflect the intensity of physical exercise, and its pathway may play a role in reactive oxygen species scavenging systems during a long-duration exercise.