Oral Administration of Melatonin to Old Ring Doves (Streptopelia risoria) Increases Plasma Levels of Melatonin and Heterophil Phagocytic Activity

Abstract

We analyzed the effect of oral melatonin (23 microg/0.1 ml/animal/d; 1 h before dark on 12 consecutive days) in old birds, in natural photoperiods, on the hormone's plasma levels, and phagocytosis. Blood collections were performed daily at 2:00 am and 4:00 pm until 5 days after the treatment. From day 1, the melatonin levels were significantly higher than basal levels at both times. Values at 2:00 am were significantly higher than the 4:00 pm values. After treatment, the melatonin levels declined, returning from day 14 to basal values at both hours. At 2:00 am, phagocytosis was significantly greater than that obtained at 4:00 pm and greater than basal values. The 4:00 pm values were only significantly greater than basal on days 6 and 8, parallel to a decline in superoxide anion levels, which were lowest at 2:00 am. Melatonin administered to old ring doves increases the differences between nocturnal and diurnal plasma levels, and, in parallel, increases phagocytosis and reduces superoxide radical levels in heterophils.