Abstract
In the past the hypothesis was advanced that plasma tryptophan fractions mediate behavioural
and neuroendocrine effects of exercise. To assess changes in free and total plasma
tryptophan levels during and after exercise over a time period, and possible functional
implications, 6 male volunteers were subjected to an endurance test of 1 hour duration
on a bicycle ergometer at a work load below the 4 mmol/1 lactate threshold. Total
and free plasma tryptophan were determined by high-performance liquid chromatography
with electrochemical detection, prolactin by radioimmunoassay, glycerol and nonesterified
fatty acids (NEFA) by enzymatic methods. No significant changes in total tryptophan
were found. Free plasma tryptophan increased significantly (23%, p < 0.01) from 40
to 60 minutes of exercise. Highest levels were observed after 10 minutes of recovery
(50% against preexercise). Prolactin levels correlated with free plasma tryptophan
throughout the test (r = 0.77, p < 0.001, all measured values) and during recovery
(10 minutes: r = 0.88, p < 0.05; 20 minutes: r = 0.86, p < 0.05). These findings may
further support the hypothesis that changes in peripheral amino acid concentrations
may influence physiological reaction of exercise mediated by brain systems.
Key words
Exercise - fatty acids - tryptophan - prolactin
