Influence of constant lighting on the morphofunctional state and rhythmostasis of the liver of rats

Abstract

BACKGROUND: There are evidences that light pollution, which causes melatonin deficiency and disruption of circadian rhythm, is associated with the development of malignant neoplasms of the liver, non-alcoholic fatty liver disease, biliary cirrhosis, and a number of other pathologies of this organ.
 AIM: The aim of research was to study the features of chronic influence of constant lighting on lability of morphofunctional state of liver of mature Wistar rats and the structure of circadian rhythms of its parameters.
 MATERIALS AND METHODS: The study was conducted on 80 rats divided into 2 groups: a control group kept under a fixed light regime (light/dark 12/12 h, lights on at 8:00 and off at 20:00), and an experimental group kept under constant lighting 24 h a day. The duration of the experiment was 3 weeks.
 RESULTS: Its established that influence of constant light led to an increase in the size of hepatocytes and a decrease in nuclear-cytoplasmic ratio, average ploidy and proportion of binuclear hepatocytes, and also to development of fatty degeneration, a decrease in the expression of Bmal1 and Clock, and an increase in the expression of per2 and p53 in hepatocytes. At the same time, there was a decrease in glycogen content in hepatocytes. Dark deprivation also caused an increase in glucose levels, AST activity, and a decrease in blood levels of total protein and albumin. Constant lighting caused a rearrangement of the circadian rhythms of the area of nuclei, the area of the hepatocyte and nuclear-cytoplasmic ratio, Bmal1, per2, Clock expression, and led to destruction of Ki67 and p53 circadian rhythms in hepatocytes. Under conditions of constant lighting, the circadian rhythms of the content of lipids and glycogen in hepatocytes, ALT activity in the blood, and the content of total and direct bilirubin were also destroyed.
 CONCLUSIONS: It has been established that constant illumination causes a restructuring of the circadian rhythms of a number of studied parameters against the background of morphological and functional changes, indicating a decrease in the adaptive capacity of the liver.