Fig. 2.

Levels of lipid peroxidase [LPO; nmol malondialdehyde (MDA)/mg protein] in heterophils from young and old ringdoves in basal, control and antigen-induced conditions in non-treated animals (a), and after 3 days of treatment 1 h before lights out with 0.25 mg/kg b.w. and 2.5 mg/kg b.w. melatonin in young and old ringdoves, respectively (b); or after 3 days of treatment 1 h after lights on with 300 mg/kg b.w. tryptophan in old ringdoves (c). Each value represents the mean ± standard deviation of six determinations performed in duplicate. Lower case letters indicate P < 0.05: a vs values obtained in the diurnal period, b vs values obtained in their respective basal groups, c vs values obtained in the corresponding control groups, d vs values obtained in young animals, e vs values obtained in the corresponding non-treated groups