Norepinephrine

Norepinephrine, also called noradrenaline, is a catecholamine that functions as both a neurotransmitter and a hormone. It is the main chemical transmitter released by most postganglionic sympathetic nerve fibers and is also produced in parts of the brain, especially noradrenergic neurons arising from the locus coeruleus. Smaller amounts enter the circulation from the adrenal medulla .¹

Norepinephrine acts on alpha- and beta-adrenergic receptors. In the peripheral sympathetic system it is especially important for regulating vascular tone and blood pressure, while in the central nervous system it contributes to arousal, attention, vigilance, and responses to stress. Its effects depend on which receptor subtype and tissue are involved .¹

Norepinephrine is closely related to epinephrine but the two are not interchangeable. Epinephrine is released predominantly as a circulating hormone from the adrenal medulla, whereas norepinephrine is more prominent as a neurotransmitter at sympathetic nerve endings. They also differ in their relative actions at adrenergic receptor subtypes. Both belong to the catecholamine family and participate in coordinating rapid physiological responses to changing demands .¹