Synchronized seasonal variation in plasma melatonin and plasma tryptophan and the immune system
Faculty of Pharmaceutical, Biomedical and Veterinary Sciences. Pharmacy
Faculty of Medicine and Health Sciences
Neuroendocrinology letters. - Weinheim
, p. 139-146
University of Antwerp
The purpose of this study was to examine the seasonal variation in plasma melatonin concentrations in relation to the availability of plasma tryptophan and the absolute number of lymphocyte subtypes in normal humans. Towards this end, 26 normal volunteers (13 men, 13 women) had monthly blood samplings for melatonin, immune and amino-acids assays during one calendar year. A significant seasonal variation is observed in plasma melatonin levels with semiannual and tetramensual rhythms. The seasonal variation in plasma melatonin is synchronized with that in the availability of plasma tryptophan and with that in the number of peripheral blood CD3+ T, CD4+ T, and CD20+ B lymphocytes. The findings suggest that the seasonal variation in plasma melatonin is synchronized by the seasonal rhythm in the availability of plasma tryptophan to the brain, and that melatonin may modulate the seasonal variations in the immune system.