Light rhythm and diet differently influence facets of the metabolic syndrome in WOKW rats

It has previously been shown that high-calorie diet alters the function of the mammalian circadian clock and that obesity has an influence on circadian organization of hormone secretion. That prompted us to test whether inbred Wistar Ottawa Karlsburg W (RT1u) (WOKW) rats developing facets of the metabolic syndrome show changes in their metabolic profiles under different feeding conditions (high-fat, high-sugar versus control diet) and under two different 12 h:12 h light–dark (LD) cycles. At the age of four weeks, these rats were divided into four groups. Groups 1 and 2 were kept under initial LD cycle (lights on at 05:00 h). Group 1 was fed with a normal rat diet while group 2 received a high-fat, high-sugar diet from 10 up to the age of 21 weeks. Groups 3 and 4 were kept under a shifted LD cycle (lights on at 11:00 h). Group 3 was given a normal diet while group 4 received a high-fat, high-sugar diet from an age like groups 1 and 2. Several metabolic traits were studied during the observation period of 21 weeks. The blood samples were obtained 2 h before lights off. Body weight gain (P < 0.001), leptin (P < 0.001), triglycerides (P < 0.001) and cholesterol (P < 0.05) were significantly reduced in group 4 versus group 2, but comparable between control groups (1 versus 3). The insulin concentrations were reduced in groups 3 and 4 versus groups 1 and 2 without effect of diet. In conclusion, the results provide evidence that light conditions influence diet induced changes in phenotypic traits like body weight gain, lipids as well as hormone levels (insulin and leptin) in WOKW rats.