ISSN 1214-0287 (on-line)
ISSN 1214-021X (printed)

Volume 6 (2008), No 4, p 177-186

The effect of tryptophanadministration on the circadian rhythms of melatonin in plasma and the pineal gland of rats

Soledad Sanchez, Cristina Lucia Sanchez, Sergio Damian Paredes, Ana Beatriz Rodriguez and Carmen Barriga

Address: Soledad Sanchez Mateos, Department of Physiology, Faculty of Science, University of Extremadura, Avda de Elvas s/n, 06071 Badajoz, Spain

Received 4th September 2008.
Revised 6th November 2008.
Published online 28th November 2008.

Full text article (pdf)

Most physiological processes that take place in the body have a circadian rhythm which is controlled by an internal biological clock located in the suprachiasmatic nucleus. The indole melatonin synthesized in the pineal gland, acts to synchronize these biological rhythms, and also it is synthesized and released following a circadian rhythm. The present study analyzed the levels of melatonin over a 24-hour period in Wistar rats in both basal and control conditions and after the oral administration of 125 mg/kg tryptophan, the amino acid that is the precursor of this indole, 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. The results indicated that the tryptophan administration provoked raised levels of melatonin at all hours studied in both plasma and pineal. Of 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), as well as an advanced acrophase with respect to the basal and control groups. In summary, our findings confirm that tryptophan intake one hour before lights-off increases melatonin levels in plasma and pineal over a 24-hour period, as well as advancing the peak of its synthesis.

circadian rhythms; melatonin; pineal gland; plasma; rat; tryptophan

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