Proceedings of The Physiological Society

Puerto de la Cruz, Tenerife (2003) J Physiol 548P, P172

Poster Communications

Effect of tryptophan on circulating levels of melatonin and the innate immune response

S. Sánchez, S.D. Paredes, A.B. Rodríguez, M.I. Martín and C. Barriga

Department of Physiology, Faculty of Sciences, University of Extremadura, 06071 Badajoz, Spain


One of the important physiological functions of melatonin, the principal hormone secreted by the pineal gland, is its immunoregulatory action (Skwarlo-Sonta, 1996; Rodríguez et al. 1999). The hormone is synthesized during the period of darkness from tryptophan, an essential amino acid in the diet. We therefore studied whether the oral administration of tryptophan influences either circulating melatonin levels or the innate immune response by evaluating the phagocytic activity of macrophages.

To this end, we used 4-month old male Wistar rats subjected to a 12 h light-12 h dark cycle. The experimental group consisted of animals (n = 6) administered tryptophan (125 mg kg-1) via an orogastric cannula half an hour before the start of the dark period (19.30 h). The control group consisted of animals under identical conditions but administered saline solution. Plasma was isolated from blood samples taken from the tail at 09.00, 21.00, and 02.00 h at the beginning of the treatment, half-way through (day 11), and at the end (day 21). On the last day, when the blood sample was taken, the animals were killed by decapitation, and macrophages were collected from the peritoneal cavity. All experiments were carried out according to the guidelines of the European Community Council Directive 86/6091 EEC. Data are expressed as mean values ± S.D. and were compared by Student's unpaired t test. Values of P

Where applicable, experiments conform with Society ethical requirements