Strenuous exercise increases plasma melatonin, cortisol, and β-endorphin concentrations. Furthermore, a relationship between endogenous opioids and melatonin has been proposed. We measured plasma melatonin, cortisol, and β-endorphin in 46 subjects before and after a 28.5-mile high altitude race. Thirteen of the subjects received the orally active opioid antagonist naltrexone immediately before the race. The mean plasma melatonin, cortisol, and β-endorphin levels were higher after the race than before it; the melatonin results were confirmed by gas chromatography-mass spectrometry assay of 12 subjects. Naltrexone had no effect on the increase in any of the three hormones. The run-induced increases in plasma melatonin, β-endorphin, and cortisol were negatively correlated with finishing time, but only the plasma β-endorphin and cortisol rises correlated with each other. We conclude that prolonged exercise in trained athletes can increase plasma melatonin and that this rise is not due to the concomitant opioid release.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Clinical Biochemistry
- Biochemistry, medical