Anticipatory changes in liver metabolism and entrainment of insulin, glucagon, and corticosterone in food-restricted rats

Restricted feeding schedules entrain behavioral and physiological circadian rhythms, which depend on a food-entrainable oscillator (FEO). The mechanis m of the FEO might depend on digestive and endocrine processes regulating e nergy balance. The present study characterizes the dynamics of circulating corticosterone, insulin, and glucagon and regulatory parameters of liver me tabolism in rats under restricted feeding schedules. With respect to ad lib itum controls, food-restricted rats showed 1) an increase in corticosterone and glucagon and a decrease in insulin before food access, indicating a pr edominant catabolic state; and 2) a reduction in lactate-to-pyruvate and be ta -hydroxybutyrate-to-acetoacetate ratios, indicating an oxidized cytoplas mic and mitochondrial redox state in the liver metabolism. All these change s were reversed after feeding. Moreover, liver energy charge in food-restri cted rats did not show a significant modification before feeding, despite a n increase in adenine nucleotides, but showed an important decrease after f ood intake. Variations detected in the liver of food-restricted rats are di fferent from those prevailing under 24-h fasting. These observations sugges t "anticipatory activity" of the liver metabolism to optimize the processin g of nutrients to daily feeding. Data also suggest a possible relationship of the liver and endocrine signals with the FEO.