his study aimed to evaluate the effects of different doses of melatonin on liver function in adult rats. Eighteen Wistar adult albino rats (Rattus norvegicus), approximately 13–16 weeks old and weighing 230 ± 10 g, were randomly divided into three groups (n=6 per group) and treated orally for 30 days as follows: Group A1 received 10 mg/kg body weight (B.W) of melatonin; Group A2 received 20 mg/kg B.W of melatonin; and the control group (Group A) received distilled water. At the end of the treatment period, blood samples were collected via cardiac puncture, and serum was separated for biochemical analysis. Parameters assessed included oxidative stress markers (malondialdehyde (MDA), reduced glutathione (GSH)) and liver enzymes (aspartate aminotransferase (AST), alanine transaminase (ALT)). The results showed that melatonin administration led to a significant (P<0.05) reduction in final body weight and a marked (P<0.01) increase in MDA and AST levels in Group A2 compared to Groups A1 and control. Conversely, in Group A1, melatonin significantly (P<0.05) reduced MDA and AST levels while significantly increasing GSH levels compared to A2 and control. No significant differences were observed in ALT levels among the three groups. Histopathological examination of liver tissue revealed vascular and sinusoidal congestion in Group A2, which was absent in Groups A1 and control. In conclusion, melatonin at a dose of 10 mg/kg B.W demonstrated beneficial effects on liver function, antioxidant status, and body weight. However, a higher dose of 20 mg/kg B.W had a detrimental impact on liver function.
