Insulin and glucagon are described to have opposing actions on hepatic glycogen metabolism. However, here we showed that their coordinated action promoted glycogen turnover and meal glucose storage. In mice, pharmacological doses of insulin or glucagon failed to alter hepatic glycogen, but the combination produced a robust decrease in glycogen content. Additivity between insulin and glucagon was also seen with the activation of hepatic insulin signaling intermediates. This signaling pathway drove glycogen synthesis, suggesting concurrent actions on glycogen breakdown and repletion. A mixed nutrient meal, which stimulates an increase in both insulin and glucagon, enhanced the incorporation of dietary glucose into hepatic glycogen. This was much more pronounced than the effects of glucose alone, which only stimulated insulin secretion. These findings revealed that glucagon is required for efficient hepatic glucose storage when acting in concert with insulin. Coordinated insulin-glucagon signaling thus emerged as a critical mechanism for hepatic glycogen cycling, challenging the classical paradigm that these hormones work in opposition.
Kejriwal et al. (Tue,) studied this question.