Correlation between the circadian rhythm of melatonin, phagocytosis, and superoxide anion levels in ring dove heterophils

A functional role for melatonin is its relationship to circadian timing mec hanisms. In addition, there has recently been assumed to be a functional co nnection between the pineal gland and the immune system in mammals and bird s, with some findings showing melatonin to be a free radical scavenger and general antioxidant. The present study investigates the possible relationsh ip between the circadian rhythm of melatonin and the ingestion capacity as well as superoxide anion levels of ring dove (Streptopelia risoria) heterop hils. In birds, heterophils, with their ability to ingest and kill differen t antigens, play a central role in the host defence mechanism. All determin ations were made during 24 hr periods at 2 hr intervals. Radioimmunoassay s howed an increase of melatonin serum levels during the dark period (from 20 :00 to 07:00 hr) with a maximum at 04:00 hr,and a significant decline durin g the hours of light with a minimum at 16:00 hr. Similary, the phagocytic i ndex was enhanced during the night, with the maximum at approximate to 04:0 0 hr and the minimum at approximate to 18:00 hr. The same was the case in r elation to phagocytic percentage. However, the superoxide anion levels were lower during darkness (minimum at 04:00 hr) and higher during the light pe riod (maximum at 14:00 hr). In conclusion, our findings show that one pinea l-mediated effect on the immune system may be a direct action of melatonin on phagocytosis and the phagocytic biochemical process, and that this neuro hormone might act as an antioxidant.