catecholamine
Catecholamines are a small family of chemically related signaling molecules that act as the body's stress messengers. The headline members are adrenaline, noradrenaline, and dopamine, and they share a common chemical backbone that gives the family its name and its behavior.
Structurally, every catecholamine has a catechol ring (a benzene ring with two adjacent hydroxyl groups) plus an amine side chain. They are built in sequence from the amino acid tyrosine: tyrosine to dopa, dopa to dopamine, dopamine to noradrenaline, and noradrenaline to adrenaline. That same catechol structure makes them rapid in onset, poorly absorbed by mouth, and quickly broken down by the enzymes monoamine oxidase and catechol-O-methyltransferase.
In autonomic pharmacology they act mainly on adrenergic receptors, with each member favoring different subtypes. As drugs they are given by infusion or injection to support the heart and blood pressure, treat anaphylaxis, and prolong local anaesthesia. Synthetic catecholamines such as dobutamine and isoprenaline extend the family with more targeted receptor profiles.
Dopamine, adrenaline, and noradrenaline are all catecholamines kept ready in the intensive care unit to support a critically low blood pressure.
The catecholamines on the critical-care shelf.
Because catecholamines are destroyed by gut and liver enzymes and absorbed poorly, they cannot be taken as a tablet; they must be given intravenously or by another parenteral route to have a useful effect.