1. A hormone secreted by the adrenal medulla that stimulates hepatic glycogenolysis, causing an elevation in the blood sugar, vasodilation of blood vessels of the skeletal muscles, vasoconstriction of the arterioles of the skin and mucous membranes, relaxation of bronchiolar smooth muscles, and stimulation of heart action.

Used in local anesthetics for its vasoconstrictive action to prolong the anesthesia action, provide hemostasis, and reduce systemic complications.

2. A white to brownish crystalline compound isolated from the adrenal glands of certain mammals or synthesized and used in medicine as a heart stimulant, vasoconstrictor, and bronchial relaxant.
3. Also called adrenalin, a secretion of the adrenal glands (along with norepinephrine) that helps the liver release glucose and limits the release of insulin.

Norepinephrine is both a hormone and a neurotransmitter, a substance that transmits nerve signals.