Physiological concentrations of melatonin and corticosterone affect phagocytosis and oxidative metabolism of ring dove heterophils

A functional connection between the neuroendocrine and the immune systems has been established. Of particular interest is the finding that hormones such as melatonin and corticosterone are able to exert modulating effects on the immune function. Therefore, after determining the circadian rhythms of melatonin and corticosterone, we evaluated the in vitro effect of physiological concentrations of melatonin and corticosterone, separately and together, on the phagocytic function and superoxide anion levels of heterophils in ring dove ( Streptopelia risoria ). Trials were performed with concentrations corresponding to the nocturnal and diurnal levels reached by each of the hormones (50:300 pg/mL and 100:10 ng/mL for melatonin and corticosterone, diurnal:nocturnal, respectively). The phagocytes were incubated with the hormones both alone and concurrently. At the highest (nocturnal) concentration, melatonin augmented phagocytic function and at the same time inducing a fall in superoxide anion levels. At the highest (diurnal) concentration, corticosterone also enhanced phagocytic function, but without modifying the phagocyte oxidative metabolism. In the presence of both hormones, however, whether with nocturnal or diurnal concentrations, there was a greater increase in phagocytic function and a decrease in superoxide anion levels than was produced by either of the hormones alone. In conclusion, our findings suggest that melatonin and corticosterone may have an additive effect in the modulation of phagocytic function.