Norepinephrine (NE), also called noradrenaline, is a molecule that functions in the human brain and body as a hormone andneurotransmitter. Those parts of the body that produce or are affected by it are referred to as noradrenergic.

Norepinephrine is synthesized and released by the central nervous system, and also by the sympathetic nervous system in the autonomic nervous system, where it is used to control the smooth muscle. It acts on target cells by binding to and activating noradrenergic receptors located on the cell surface.

Epinephrine或肾上腺素,是一种非常相似的分子controls the smooth muscle in the same way as norepinephrine does. There are only slight differences between them, such as their chemical structure (Figure 1) and their affinity for adrenergic receptors, which is greater for alpha receptors in the case of epinephrine.

Figure 1. Norepinephrine and epinephrine chemical structures.Epinephrine is usually synthesized from norepinephrine after the addition of a methyl group to the nitrogen by the phenylethanolamineN-methyltransferase. Because of this, epinephrine is also known asmethylated norepinephrine.