Epinephrine

Epinephrine, also called adrenaline, is a catecholamine that functions mainly as a hormone released from the adrenal medulla, although it can also act as a neurotransmitter. Its secretion rises during activation of the sympathetic stress response and it acts through alpha- and beta-adrenergic receptors in many tissues .¹

Epinephrine helps coordinate rapid responses to physical or psychological stress. Depending on the receptor and tissue, it can increase heart rate and cardiac output, relax airway smooth muscle, alter blood vessel tone, and mobilize metabolic fuels by promoting processes such as glycogen breakdown and lipolysis. These effects help redistribute oxygen and energy substrates when demand changes quickly .¹

Epinephrine is closely related to norepinephrine but is not identical to it. Norepinephrine is the principal neurotransmitter released by most postganglionic sympathetic nerves, whereas circulating epinephrine is produced predominantly by the adrenal medulla. Both act on adrenergic receptors, but their receptor preferences and physiological roles differ, so the two names should not be used interchangeably .¹