Conclusion
CR induces lipid insufficiency and stress, resulting in global physiological insulin resistance except muscle and enhances glycogen metabolism, culminating in the stability of blood glucose manifests in increased FBG, which compensates for insufficient blood ketones.
Results
CR mice exhibit super-stable blood glucose, as evidenced by increased fasting blood glucose (FBG), decreased postprandial blood glucose, and reduced glucose fluctuations. Additionally, both fasting plasma insulin and the homeostasis model assessment of insulin resistance increase significantly in CR mice. Compared with control, the phosphorylation of insulin receptor substrates-1 and serine/threonine kinase decreases in liver and fat but increases in muscle of CR mice after insulin administration, indicating hepatic and adipose insulin resistance, and muscle insulin sensitization. CR reduces visceral fat much more than subcutaneous fat. The elevated FBG is negatively correlated with low-level fasting β-hydroxybutyrate, which may result from insufficient free fatty acids and diminishes ketogenic ability in CR mice. Furthermore, liver glycogen increases dramatically in CR mice. Analysis of glycogen metabolism related proteins indicates active glycogen synthesis and decomposition. Additionally, CR elevates plasma corticosterone and hypothalamic orexigenic gene expression.