Does glucagon promote glycogenesis or glycogenolysis?

Glucagon primarily promotes glycogenolysis, which is the process of breaking down glycogen into glucose. This hormone is produced by the pancreas in response to low blood glucose levels. When glucose availability is low, glucagon acts to increase the concentration of glucose in the bloodstream, facilitating energy supply, especially for tissues like the liver and muscles.

The mechanism behind this involves glucagon binding to its receptor on liver cells, which activates a signaling cascade that ultimately leads to the activation of enzymes responsible for glycogen breakdown. These enzymes include glycogen phosphorylase, which catalyzes the release of glucose-1-phosphate from glycogen stores.

In contrast, glycogenesis is the synthesis of glycogen from glucose, a process that is stimulated by insulin, particularly after meals when glucose levels are elevated. Therefore, glucagon and insulin have opposing effects regarding glycogen metabolism. Glucagon's primary role is to ensure that blood glucose levels remain stable during fasting or between meals, emphasizing its function in glycogenolysis over glycogenesis.