Melatonin effect on plasma adiponectin, leptin, insulin, glucose, triglycerides and cholesterol in normal and high-fat fed rats

Melatonin effect on body weight progression, mean levels and 24‐hour pattern of circulating adiponectin, leptin, insulin, glucose, triglycerides and cholesterol were examined in rats fed a normal or a high‐fat diet. In experiment 1, rats fed a normal diet were divided into two groups, receiving melatonin (25 μg/mL drinking water) or vehicle for 9 weeks. In experiment 2, animals were divided into 3 groups, two fed with a high‐fat diet (35% fat) and melatonin (25 μg/mL) or vehicle in drinking water for 11 weeks, while a third group was given a normal diet (4% fat). At the end of experiments groups of 8 rats were killed at 6 different time intervals throughout a 24 hour period. Melatonin administration for 9 weeks decreased body weight gain from the 3rd week on without affecting food intake. A significant reduction of circulating insulin, glucose and triglyceride mean levels and disrupted daily patterns of plasma adiponectin, leptin and insulin were observed after melatonin. In high‐fat fed rats, melatonin attenuated body weight increase, hyperglycemia and hyperinsulinemia, as well as the increase in mean plasma adiponectin, leptin, triglycerides and cholesterol levels. The high‐fat diet disrupted normal 24 h patterns of circulating adiponectin, insulin and cholesterol, the effects on insulin and cholesterol being counteracted by melatonin. Nocturnal plasma melatonin concentration in control and obese rats receiving melatonin for 11 weeks attained values 21‐24‐fold greater than controls. The results indicate that melatonin counteracts some of the disrupting effects of diet‐induced obesity in rats