The immune system function has a circadian rhythm. Exogenous administration of the amino acid tryptophan increases the release of the neurohormone melatonin (Hajak et al. 1991). This pineal hormone increases phagocytosis and decreases oxidative stress (Rodríguez et al. 2002). The purpose of the present work was to evaluate the ingestion capacity and oxidative metabolism in heterophils from ring dove (Streptopelia roseogrisea) after 7 days administration of 125 mg L-tryptophan (kg b.w.)-1.
The birds (n = 15) were maintained under a 12 h light (3000 lux)-12 h dark cycle and handled according to the guidelines of European Community Council Directives 86/6091 EEC. Tryptophan was administrated at 19.00 h (1 h before darkness). Phagocytosis and superoxide anion levels were measured in heterophils (isolated by a density gradient with Ficoll) at 21.00 h (2 h after administration of the amino acid) and at 02.00 h, using MIF plates and the NBT reduction test respectively. All experiments were carried out according to the guidelines of the European Community Council Directive 89/6091 EEC. Data are expressed as mean values ± S.E.M. and were compared by Student’s unpaired t test. Values of P ²le³ 0.05 were considered significant. Results are expressed as a phatocytosis index (PI, number of latex beads ingested by one hundred heterophils), phagocytosis percentage (PP, percentage of heterophils which have phagocytosed at least one latex bead), and phagocytic efficiency (PE, mean number of latex beads phagocytosed by each heterophil that has phagocytosed at least one latex bead). The NBT reduction test results are expressed as the percentage of the absorbency at 525 nm of the stimulated samples relative to the non-stimulated samples.
The results showed the PI after tryptophan administration to be higher (P < 0.05) at 02.00 h (79.38 ± 11.02 vs. 41.86 ± 10.65 control values), due to a greater phagocytic efficiency of the heterophils at that h (PE 2.52 ± 0.6 vs. 1.76 ± 0.18 control values). Superoxide anion levels were significantly lower in the tryptophan group (P < 0.05) at 02.00 h (59.24 ± 4.11) with respect to both the controls (100) and the values obtained at 09.00 h in the tryptophan group (107.77 ± 8.88).
In conclusion we suggest that administration of L-tryptophan increases the phagocytic capacity of heterophils and decreases superoxide anion levels at 02.00 h, at which hour there are elevated levels of melatonin.
The authors thank Elena Circujano Vadillo for technical assistance and the Laboratories Ordesa S.L. for their collaboration. This research was supported by the Ministerio de Ciencia y Teconología AGL 2000-0182-P4-03.