Aim: 

The present study analyzed the effect of administration of tryptophan on circadian rhythms of melatonin in plasma and pineal gland in rats.

Methods: 

We used male Wistar rats of 14 2 weeks of age (n = 360), maintained under conditions of 12 hours light and 12 dark. Animals were treated for 7 consecutive days with a single daily oral dose (125 mg / 1 ml saline solution) of L-tryptophan at 19:00 (one hour before light turn off) using a gavage needle. Control rats received only 1 ml of saline solution with the same schedule as the tryptophan-treated animals. The tryptophan was administered for 7 days. The levels of melatonin in the plasma and the pineal gland were measured by radioimmunoassay every hour during the night, and every 4 hours during the day.

Results: 

The results indicated that the tryptophan administration provoked raised levels of melatonin at all hours studied in both plasma and pineal. Regarding the chronobiological parameters studied, there were also increases in the values of the melatonin MESOR with respect to the values obtained in the basal and control groups (the respective increases being 45% and 52% in plasma, and 46% and 47% in the pineal gland), as well as an advanced acrophase with respect to the basal and control groups.

Conclusion: 

Our findings confirm that tryptophan intake one hour before lights-off increases melatonin levels in plasma and pineal gland over a 24-hour period, as well as advancing the peak of its synthesis.