Physiological concentrations of melatonin and corticosterone in stress and their relationship with phagocytic activity.

The aim of the present work was to investigate the possible connection between melatonin, corticosterone and the nonspecific immune response under both basal and stressed conditions. The concentrations used in the present study were as determined in an earlier work, and corresponded to the minimum and maximum concentrations of the hormones melatonin and corticosterone over one circadian cycle in mice subjected to stress and in a basal group of mice. The concentrations were 15 pg/ml and 90 pg/ml of melatonin and 50 ng/ml and 200 ng/ml of corticosterone for incubations of the basal group macrophages, and 15 pg/ml and 70 pg/ml and 200 ng/ml and 500 ng/ml of melatonin and corticosterone, respectively, for incubations of macrophages from the group of stressed mice. The results indicate that corticosterone stimulates antigen ingestion at all physiological doses tested in the macrophages from the unstressed mice. The greatest phagocytic stimulation was obtained in macrophages from mice in a basal situation, and which had been incubated with the diurnal concentrations of the two hormones (maximum corticosterone 200 ng/ml; minimum melatonin 15 pg/ml). When the macrophages were from stressed mice, neither corticosterone nor melatonin led to any change in their phagocytic activity.