catecholamine

Catecholamines are a family of fast-acting signaling molecules that the body uses for alertness, arousal, and emergencies. Unlike the slow steroid hormones of the adrenal cortex, catecholamines act within seconds and fade quickly — perfect for a rapid-response system. The three main members are epinephrine, norepinephrine, and dopamine.

Chemically they are amine hormones built from the amino acid tyrosine, and they all share a catechol ring (a benzene ring with two adjacent hydroxyl groups) attached to an amine — hence the name. Because they are water-soluble, they cannot cross cell membranes and instead act on cell-surface receptors (adrenergic receptors), triggering rapid second-messenger signals inside target cells.

Catecholamines work in two overlapping roles: as neurotransmitters released by nerve endings, and as hormones poured into the blood by the adrenal medulla during stress. Their effects — faster heart rate, higher blood pressure, dilated airways, and mobilized glucose — define the fight-or-flight state. They are broken down rapidly by enzymes (MAO and COMT), which is why their actions are brief unless production keeps up.