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 μg/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. Copyright 2005 by The Gerontological Society of America.