Can cortisol and catecholamines raise fasting glucose even when fasting insulin is normal?

The regulation of fasting blood glucose is a dynamic process where the liver's glucose output is determined by the balance between insulin’s suppressive effects and the stimulatory actions of counter-regulatory hormones.

Mechanistic insights

The liver employs two primary pathways to increase glucose availability in response to stress hormones:

• Glycogenolysis: Catecholamines, specifically epinephrine, trigger a rapid increase in hepatic glucose output (HGP) by stimulating the breakdown of stored glycogen. This occurs through cAMP/PKA signaling pathways that activate glycogen phosphorylase, potentially increasing HGP by 4–5 fold within an hour of a surge.
• Gluconeogenesis: Cortisol operates on a longer timescale, primarily promoting the synthesis of new glucose from non-carbohydrate sources. It achieves this by upregulating the expression of key rate-limiting enzymes, such as phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase). While cortisol has a modest effect alone, it is essential for amplifying the glucose-raising effects of epinephrine and glucagon.

Clinical evidence and insulin dynamics

Evidence from metabolic studies demonstrates that elevated cortisol and catecholamines can cause fasting hyperglycemia even when fasting insulin remains within a "normal" laboratory range (e.g., 2–12 µIU/mL).

• Hormonal Overdrive: Controlled experiments using somatostatin to maintain constant basal insulin show that cortisol and epinephrine infusions significantly increase glucose appearance rates. This suggests these hormones can "override" the suppressive signaling of normal insulin levels.
• Insulin Antagonism: Cortisol directly contributes to transient hepatic insulin resistance, reducing the liver's sensitivity to circulating insulin. Simultaneously, catecholamines can inhibit insulin secretion from the pancreas via alpha-2 adrenergic receptors, further tilting the metabolic balance toward glucose production.
• Physiological Phenotypes: This mechanism is frequently observed in the "Dawn Phenomenon" and during acute psychological or physical stress, where glucose rises due to hormonal surges that exceed the compensatory capacity of baseline insulin.

Bottom line

Cortisol and catecholamines synergistically increase hepatic glucose output via rapid glycogenolysis and sustained gluconeogenesis. These hormones can elevate fasting glucose levels despite normal fasting insulin by directly antagonizing insulin’s action and overwhelming its ability to suppress hepatic glucose production.