Which hormone elevates blood glucose by stimulating gluconeogenesis in the liver?

• A. Glucagon
• B. Insulin
• C. Growth hormone
• D. Cortisol

Answer: (A)

Glucagon raises blood glucose by signaling the liver to produce glucose through gluconeogenesis and, to some extent, glycogen breakdown, especially during fasting. It binds to receptors on hepatocytes and activates a cascade via cyclic AMP and protein kinase A, which increases the transcription and activity of gluconeogenic enzymes such as PEP carboxykinase and glucose-6-phosphatase. This shifts liver metabolism toward glucose production from non-carbohydrate substrates like amino acids, lactate, and glycerol, raising blood sugar. It also dampens glycolysis by lowering fructose-2,6-bisphosphate, further favoring glucose output. In contrast, insulin suppresses hepatic glucose production, growth hormone raises blood glucose mainly through insulin resistance and lipolysis rather than direct gluconeogenesis, and cortisol does stimulate gluconeogenesis as well but glucagon is the rapid, direct regulator of hepatic glucose output in the fasting state.