Alterations in Plasma Free Tryptophan and Large Neutral Amino Acids Do Not Affect Perceived Exertion and Prolactin During 90 min of Treadmill Exercise

Abstract

It has been hypothesized that fatigue and prolactin (PRL) changes during endurance exercise are influenced by serotonin synthesis, and in turn, release. Such a change is thought to occur through an increase in blood free tryptophan (TRP) and a concomitant decrease in those large neutral amino acids (LNAA) which compete with free TRP for entry into the brain. For further investigation, 10 healthy athletes were randomly subjected to three test units (TU), each consisting of a treadmill run for 90 min. The speed was adjusted to a blood lactate level of 2 mmol/l. During the first 30 min of exercise infusions of 500 ml saline (TU I), 500 ml saline with amino acids (TU II) or 500 ml saline with 30 U heparin/kg following an oral soy oil solution given 1 h before (TU III) were administered. Rate of perceived exertion (RPE), heart rate and running speed were recorded during exercise. Venous blood samples were taken after a 10 h fast, at rest, after 10, 50 and 90 min of exercise as well as 10 and 30 min post-exercise. PRL, insulin, glucose, ammonia, lactate, triglycerides (TG), free fatty acids (FFA) and amino acids were determined in each sample. No significant differences were found in RPE. PRL increased (p < 0.01) in all TU. TG and heparin administration resulted in an increase (p <0.01) in FFA, which correlated (p < 0.01) with free TRP and the ratio of free TRP/TRP. Artificial increase in free TRP in TU III did not affect plasma PRL level. The amino acid infusion in TU II induced an increase in LNAA but had no significant effect on PRL. PRL and ammonia peaked at the end of exercise. We conclude that neither exercise-induced PRL secretion nor RPE are affected by changes in circulating free TRP and LNAA under the present conditions.

Exercise Increases Tryptophan Availability to the Brain in Older Men Age 57–70 Years

“…The present elevations in free TRP/BCAA are in line with previous data obtained in younger men in response to moderate-intensity exercise. That is, when compared with previous studies of at least ~60 min of moderate-intensity exercise, the magnitude of increase in free TRP (-M04%) or free TRP/BCAA (+102%) from baseline levels observed in our study with older men was higher than most results reported in younger individuals (3,24,34). Nevertheless, greater elevations were observed in a study involving a regimen designed to lower muscle glycogen before exercise (40).…”

Peripheral markers of central fatigue in trained and untrained during uncompensable heat stress

“…Other studies have also reported increases in PRL which peaked at EXH with treadmill running (Struder et al 1996), following 5 h of cycling in trained individuals (Struder et al 1999), in heat acclimated men during EHS when hypohydrated (Cheuvront et al 2004), and in moderately (Melin et al 1988) and highly fit (Radomski et al 1998;Watson et al 2005a) individuals during exercise in the heat. Although T c was reported by Melin et al (1988), regression analysis was used to estimate the linear relationship between plasma PRL and T c .…”

Brain serotonergic and dopaminergic modulators, perceptual responses and endurance exercise performance following caffeine co-ingested with a high fat meal in trained humans

“…Previous studies have demonstrated that elevation in plasma [FFA] displaces Trp from binding to albumin and consequently increases the free-Trp:LNAA ratio into the plasma [17,18,30,31]. Since Trp and the other LNAAs share the L-system carrier for crossing the BBB, the elevation in plasma free-Trp:LNAA ratio may favour brain Trp uptake and potentially increase brain 5-HT synthesis [32], and hence central fatigue [15,33].…”