The effect of dark deprivation on the morphofunctional state and rhythmostasis of the liver under CCl₄ toxic exposure has been studied. The relevance of this study is due to the fact that the hepatotoxic effect of carbon tetrachloride on the liver is well studied, but there are very few data on the relationship between CCl₄ intoxication and circadian biorhythms, and most of the studies consider the susceptibility of the organism in general and of the liver in particular to the influence of CCl₄ in some separate periods of the rhythm, but not the influence of this chemical agent on the structure of the whole rhythm. In addition, earlier studies indicate that light disturbance causes certain changes in the morphofunctional state of the liver and the structure of the circadian rhythm of a number of parameters. As a result of this study, we found that the effect of CCl₄ in conditions of prolonged dark deprivation causes more significant structural and functional changes in hepatocytes, as well as leading to significant changes in the circadian rhythms of a number of parameters, which was not observed in the action of CCl₄ as a monofactor. We assume that the severity of structural and functional changes is due to the light-induced deficiency of melatonin, which has hepatoprotective properties. Thus, the mechanisms of CCl₄ action on CRs under conditions of light regime violations leave a large number of questions requiring further study, including the role of melatonin in these processes.

Background: Chronic exposure to artificial light at night (light pollution) causes circadian desynchronosis and melatonin deficiency, which is considered an independent driver of metabolic disorders and accelerated aging. However, the long-term effects of chronic desynchronosis on systemic metabolism and liver structure throughout the life cycle, as well as the potential of preventive melatonin administration, remain poorly understood. Objective: To evaluate the effects of chronic dark deprivation and prevention of metabolic disorders by exogenous melatonin on plasma melatonin levels, metabolic profile, liver function, and morphological changes in rats over a 24-month experiment. Methods: A 24-month experiment was conducted on 360 male Wistar rats divided into three groups: control (standard 10:14 h light/dark photoperiod), dark deprivation (DD, constant illumination), and correction (DD+Mel, constant illumination + melatonin 10 mg/kg five times per week). Animals were sacrificed at 6, 12, 18, and 24 months. Plasma melatonin was assessed by ELISA. Biochemical parameters (ALT, AST, LDH, total protein, albumin, bilirubin, glucose, triglycerides, and cholesterol), body weight, liver weight, relative liver weight, and histological parameters (steatosis, fibrosis, nuclear area, nuclear/cytoplasmic ratio, and binucleated hepatocytes) were analyzed. Results: In the DD group, a persistent progressive melatonin deficiency was detected (5.1-fold decrease by 6 months, p < 0.0005), accompanied by hypertriglyceridemia (Cohen’s d = 6.40), hypercholesterolemia (d = 4.59), biphasic dysglycemia (hypoglycemia followed by hyperglycemia), elevated ALT and AST activity (d = 2.60 and 2.46, respectively), hypoproteinemia (d = 5.33), hypoalbuminemia (d = 3.34), and hyperbilirubinemia (d = 3.22–4.37), as well as progressive steatosis (2.8 ± 0.3 points, d = 7.20) and pericellular fibrosis (1.8 ± 0.4 points, d = 4.50). In the DD group, a decrease in relative liver weight during the first 12 months was observed (metabolic disproportion, d = 2.31), reflecting disproportionate body weight gain. In the DD+Mel group, exogenous melatonin restored the biochemical parameters to values that did not differ statistically from the control values (Cohen’s d < 0.2 for most parameters), prevented steatosis (0.8 ± 0.3 points, d = 0.80) and fibrosis (0 points), increased relative liver weight by 24 months (3.83 ± 0.49 vs. 3.27 ± 0.029 in the control, d = 1.60), and increased the hepatocyte nuclear area (58.4 ± 4.1 vs. 48.6 ± 3.8 μm², d = 2.32). Conclusions: Chronic desynchronosis induced by constant illumination leads to persistent melatonin deficiency and complex metabolic and structural liver disturbances modeling accelerated aging. Exogenous melatonin (10 mg/kg five times per week) exhibits pronounced geroprotective, hepatoprotective, and antifibrotic effects, normalizing all biochemical parameters and preventing age-related liver involution.

Circadian rhythm disruption induced by exposure to light—excessive in duration and intensity (dark deprivation)—and the impact of hepatotoxins are both significant risk factors for liver pathology. The purpose of this research was to evaluate the potentially synergistic effects of continuous lighting and carbon tetrachloride (CCl₄) toxicity on the structural and functional organization and daily (circadian) rhythmicity of the liver in rats, as well as to look at the corrective capability of exogenous melatonin under such influences. The experiment was conducted on 200 outbred 6-month-old Wistar rat males, which were distributed into five groups, including a control (normal light/dark cycle), dark deprivation (constant light), CCl₄ intoxication, and combined exposure to CCl₄ and dark deprivation with or without melatonin administration (0.3 mg/kg). Histological, immunohistochemical (Ki-67, Per2, and Bmal1), biochemical, and ELISA methods were used. Circadian rhythms were analyzed using cosinor. It was shown that dark deprivation and CCl₄ intoxication act synergistically, potentiating liver damage. The most severe necrosis (54.17 ± 9.13%), steatosis (57.85 ± 12.14%), and suppression of regenerative potential (decreased proportion of binucleated hepatocytes to 2.17 ± 0.21%) were observed in the group with combined exposure. This correlated with a substantial decline in melatonin content in blood plasma (7.85 ± 2.1 pg/mL) and a profound disruption in circadian rhythms. Administration of exogenous melatonin exerted pronounced hepatoprotective and chronotropic effects: it significantly reduced pathological changes (necrosis reduced to 16.35 ± 6.17%), stimulated regeneration (binucleated hepatocytes increased to 13.57 ± 0.81%), and restored the circadian rhythms of the studied parameters to levels close to those of the control. The key pathogenetic link in the potentiation of CCl₄ hepatotoxicity under dark deprivation is light-induced deficiency of endogenous melatonin. Exogenous melatonin demonstrated high efficacy in correcting both structural and functional damage and liver desynchronosis, confirming its therapeutic potential under conditions of combined exposure to chronodisruptors and toxins.

Disruption of circadian rhythms caused by constant artificial lighting (“light pollution”) is a significant risk factor for the development of metabolic and age-associated pathologies. The liver, as a central metabolic organ with pronounced circadian regulation of its functions, is particularly vulnerable to desynchronosis. The aim of this study was to evaluate the effect of three-month dark deprivation (constant lighting) and the corrective action of exogenous melatonin on the morphofunctional state of the liver in young mature rats. The experiment used 3-month-old male Wistar rats, divided into groups: control (standard light:dark cycle 10:14 h), dark deprivation group (DD, constant lighting 24 h/day), and DD + Melatonin group (DD + Mel, dark deprivation with melatonin administered in drinking water at a dose of 12 mg/L). After 3 months (animal age 6 months), a comprehensive analysis was performed. It was shown that dark deprivation causes a profound (more than five-fold) suppression of plasma melatonin levels, which is accompanied by the formation of a pro-senescent and metabolically dysfunctional phenotype of the liver. This was manifested by the development of steatosis, an 18% increase in hepatocyte area, a 30% decrease in the proportion of binucleated hepatocytes, activation of cellular senescence markers (p16, p21) and stress markers (p53), and suppression of the expression of circadian transcription factors BMAL1 and CLOCK. At the ultrastructural level, lipofuscin accumulation, damage to mitochondria and the Golgi apparatus were noted. Biochemically, hyperglycemia, increased AST activity, hypoproteinemia, hypoalbuminemia, hypercholesterolemia, and hypertriglyceridemia were revealed. Administration of exogenous melatonin completely prevented the development of these disorders, normalizing hormone levels, morphology, ultrastructure, biochemical parameters, and the expression of key molecular markers. Thus, three-month dark deprivation induces complex pro-senescent remodeling and metabolic dysfunction of the liver, mediated by melatonin deficiency, while exogenous melatonin demonstrates a pronounced hepatoprotective and chronoprotective effect.

BACKGROUND: To correctly interpret preclinical studies and basic research, it is necessary to accurately assess the biometric parameters of normal status and their limits. Biometric parameters of animals of genetically pure lines are known to vary according to factors such as sex and age, but little attention is paid to a seasonal factor. Therefore, it seems relevant for physiology and pathophysiology to develop reference values of normal status and their limits for working with genetically pure animals during certain periods of ontogenesis and different seasons. AIM: The aim of the study was to determine the absolute body and organ weights and the relative organ weights of adult male Wistar rats at three months of age during different seasons of the year. MATERIALS AND METHODS: The experiment involved 160 male Wistar rats. The animals were divided into four groups so that the rats reached the age of three months in one of the seasons: spring, summer, fall, or winter. In each group, absolute and relative body and organ weights were measured for the brain, spleen, thymus, liver, kidneys, adrenal glands, heart, lungs, and testes. RESULTS: The most significant seasonal differences were found in the absolute weights of all organs, while the relative weight coefficients of the organs differed in only 50% of the cases. Synchronous seasonal differences in kidney and adrenal gland weights were observed. The heart was found to have the most significant seasonal variability in both weight parameters studied. CONCLUSIONS: The absolute organ weight is one of the most sensitive parameters in determining reference values, but changes in the relative weight coefficient should also be considered. This study established reference ranges for the weight of major organs in a population of healthy, genetically homogeneous Wistar rats at three months of age and showed seasonal variations in these reference ranges. Further research is needed to understand changes in organ weights combined with pathological data.

BACKGROUND: Today it is known that disturbance of the lighting regime, expressed both by lengthening of the light period and its reduction, can not only affect the regulation of circadian rhythms of the organism, but also contributes to the initiation of neoplasm growth. AIM: The aim of the study was to investigate circadian rhythmicity of melatonin level, some micromorphometric indices of tumor cells and expression of genes Bmal1, Clock and Per2 in them in mice with transplanted melanoma B16. MATERIALS AND METHODS: The study was conducted on 75 mice with subcutaneously transplanted melanoma B16, divided into 3 groups: control group, in which animals were kept under fixed light regime (light/darkness 10/14 hours with light on at 8:00 and off at 18:00), group under dark deprivation conditions, with animals kept under constant light 24 hours a day and group, in which animals were kept in constant darkness. The duration of the experiment was 2 weeks. RESULTS: It was shown that under conditions of fixed light there are reliable circadian rhythms for all studied parameters, except for the nuclear-cytoplasmic ratio, the circadian rhythms of which was not revealed in any group. Constant darkness leads to rearrangement of all identified rhythms, and constant light causes destruction of all circadian rhythms except the Clock expression rhythm. CONCLUSIONS: This study shows that light disturbances, whether constant light or constant darkness, lead to significant changes in the structure of the studied circadian rhythms.