Carbohydrate metabolism in the rats’ liver under conditions of light and dark deprivation and correction by melatonin

Aim This study aimed to investigate changes in carbohydrate metabolism in the liver of rats under light and dark deprivation and evaluate the effects of melatonin treatment. Material and methods Photoperiodic changes were simulated over two weeks: the natural equinox (March 16-29); the artificial equinox (12:12 light-dark cycle, 500 lux); constant light (24 hours, 500 lux) for dark deprivation; and constant dark (24 hours, 0-0.5 lux) for light deprivation. Forty-eight rats were divided into control and melatonin-treated groups (5 mg/kg daily for 14 days). Enzyme activities and glycogen content in the liver were measured using standard methods. Statistical analysis was performed using the Student’s t-test. Results Glucose-6-phosphate dehydrogenase activity decreased by 18% under constant light but increased by 35% under constant dark compared to the equinox. Pyruvate kinase activity decreased by 17%, while glucose-6-phosphatase and lactate dehydrogenase activities increased by 9% and 20%, respectively, under constant light. Constant dark and melatonin treatment reduced glucose levels by 26% across all conditions, activated aerobic pathways, and increased glycogen content by 13% compared to the equinox. Conclusions Melatonin treatment improved carbohydrate metabolism in the liver of rats under light and dark deprivation, suggesting its role in metabolic adaptation to altered photoperiods.