Pharmacologically, glucagon is the most potent of the hyperglycaemic hormones (Fig. 20.7). Its secretion is important, but not essential, in raising the concentration of blood glucose depressed by previous exogenous or endogenous insulin, providing that the sympathetic nervous system is intact. Glucagon exerts its hyperglycaemic effects exclusively through the liver by liberating glucose from preformed glycogen, by increasing glycogenolysis and, to a lesser extent, by increasing gluconeogenesis from glucose precursors.
