Changes in the Interaction of the Pineal Gland and Immune System Organs in Rats in Response to Administration of Melatonin in Conditions of an Altered Light Regime

The aim of the present work was to use correlation analysis to identify the complex reaction of the pineal gland (PG) and immunocompetent organs in response to administration of melatonin (MT) in conditions of an abnormal light regime. Animals were kept for 14 days with natural or round-the-clock illumination (RTCI). Animals then received 0.9% sodium chloride solution or MT for seven days, after which they were decapitated and measurements were made of body, PG, thymus, and spleen weight. Thymus and spleen lymphocyte subpopulations were assessed by flow cytometry. PG lipofuscin content was determined in terms of autofluorescence intensity on frozen sections at wavelengths over the range 560–600 nm. The number of intraorgan relationships within the immune system was found to increase in response to MT regardless of light regime. Administration of MT to animals subjected to RTCI decreased the number of interorgan relationships, with the appearance of negative correlations between PG lipofuscin content and the cellular composition of the spleen. The most marked synchronizing and adaptogenic effects of MT were seen in RTCI conditions.