[The problems of the central regulation of immune system biorhythms: the role of exogenous and endogenous melatonin].
One of the key synchronizers of mammalian circadian rhythm is the hormone melatonin (MT) produced by the pineal gland. MT is characterized by a wide spectrum of biological activity including its immunopotentiating effect. At the same time, the results of studies dedicated to the effects and mechanisms of melatonin immunoactivity seem to be contradictory. Studies conducted by the authors of this article show that diurnal variations in MT content in blood and saliva of healthy humans demonstrate significant individual fluctuations connected with the seasonal factor. The character of MT relations with the immune system varies depending on the phase of the circadian cycle. Patients with immunopathological condition (bronchial asthma--BA) demonstrate a reduced number of correlations between MT level and immunological parameters. After treatment, the positive dynamics of immunological and clinical parameters in BA patients is associated with an increased number of correlations between the immunological status parameters and MT level in blood, which may indicate an increase in its immunoregulatory role. Administration of melatonin and amitriptyline, the inductor of its synthesis, in animals kept under continuous light helped to recover normal circadian rhythmicity in the cell content of lymphoid organs. Solving problems associated with the immunomodulating and synchronizing role of MT could give researchers an insight into the details of neuroendocrine and immune interrelations and help to develop new methods for the prevention and correction of immune status disturbances in diseases and desynchronoses (stresses, jet lags, shift and night work, etc.).