What effects does norepinephrine have on blood vessels and blood glucose?

Norepinephrine, a catecholamine that functions as both a neurotransmitter and a hormone, plays a critical role in the body's fight-or-flight response by modulating cardiovascular and metabolic functions.12

Effects on Blood Vessels

Norepinephrine acts primarily on $\alpha$-adrenergic receptors in blood vessels, triggering vasoconstriction (the narrowing of blood vessels). This action increases total peripheral resistance and contributes to a rise in blood pressure. While epinephrine may cause vasodilation in certain tissues, norepinephrine is characterized by its consistent vasoconstrictor effect, which helps redistribute blood flow during acute stress.132

Effects on Blood Glucose

Norepinephrine influences nutrient metabolism to ensure the body has sufficient fuel during emergencies. It acts to increase blood glucose levels, primarily by stimulating glycogenolysis—the breakdown of liver glycogen into glucose. Additionally, it promotes the breakdown of triglycerides into free fatty acids, further supporting the body's energy demands. Compared to epinephrine, norepinephrine typically has a more modest effect on blood sugar levels.312