Reactivity of the stress-realizing system under changing light conditions in the experiment

The effect of the duration of light exposure (model 18:6) on the hormonal indicators of the stress-releasing system in the blood of laboratory animals was studied. The activity of the central part of the stress-relieving system was estimated on the basis of data on the concentration of adrenocorticotropic hormone, melatonin and $\beta$-endorphin in blood serum obtained by enzyme immunoassay. The response of the peripheral link of the stress-releasing system was evaluated in blood smears by quantitative counts of catecholamine granules in erythrocytes. It was found that the fluctuations of stress system hormonal indices in laboratory animals depended on the duration of the trigger factor. When the duration of the experiment increases up to 21 days, the most pronounced decreases in serum melatonin, $\beta$-endorphin and increases in adrenocorticotropic concentrations, as well as a sharp increase in catecholamine levels are observed. These hormonal changes develop as a result of the failure of the compensation mechanisms of the stress-releasing systems against the background of melatonin rhythm disturbances, which indicates the stage of development of the general adaptation syndrome.