The oral administration of tryptophan improves nocturnal rest in young animals: Correlation with melatonin

摘要

The amino acid tryptophan has a clear mechanism inducing a hypnotic function by way of synthesis of the hormone melatonin. Certain concentrations of the amino acid are known to raise the circulating levels of melatonin, but its possible effects on the activity/rest cycle have yet to be fully elucidated. Tryptophan was administered orally at the pharmacological dose of 300 mg/kg b.w. for 7 days at the start (09:00, one hour after lights on) and at the end (19:00, one hour before lights off) of the light period to ringdove (Streptopelia roseogrisea), a diurnal and monophasic animal, of less than six months in age. The activity/rest rhythms were evaluated during the entire 7 days of the treatment, and plasma melatonin was determined on days 1, 3, and 7. The tryptophan administration led to a decline in nocturnal activity, independently of the time of administration. The circulating levels of melatonin at 02:00 h (the acrophase of this hormone in basal conditions) were raised on all three days on which they were measured. These results indicate that tryptophan administration reduces nocturnal activity at the same time as increasing the nocturnal levels of melatonin, the hormone responsible for regulating the sleep/wake rhythm. Oral supplementation of this essential amino acid during the first months of life is suggested as an aid to improving nocturnal rest.