Catecholamine

Catecholamines are a class of monoamine neurotransmitters and hormones derived from the amino acid tyrosine. They share a catechol group and an amine side chain. The principal members are dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline). They are produced in the sympathetic nervous system and the adrenal medulla and play key roles in regulating cardiovascular function, metabolism, and central nervous system activity.

Biosynthesis and storage occur in a sequence beginning with tyrosine being converted to L-DOPA by tyrosine hydroxylase, the rate-limiting step. L-DOPA is decarboxylated to dopamine, which is then hydroxylated to norepinephrine by dopamine beta-hydroxylase in vesicles. In chromaffin cells of the adrenal medulla, norepinephrine can be converted to epinephrine by phenylethanolamine N-methyltransferase. Catecholamines are stored in synaptic vesicles by VMAT2 and released into the synapse by calcium-dependent exocytosis. They are rapidly cleared from the synapse by reuptake transporters—NET for norepinephrine, DAT for dopamine—and degraded by enzymes such as monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT).

Functionally, catecholamines act as neurotransmitters in the brain and as hormones in the peripheral circulation. Dopamine influences movement, motivation, and reward pathways; norepinephrine modulates alertness, attention, vascular tone, and blood pressure; epinephrine is a key mediator of the fight-or-flight response, increasing heart rate, bronchodilation, and energy mobilization.

Clinical relevance includes disorders of catecholamine signaling and secretion. Excess catecholamines can arise from pheochromocytoma, causing hypertension and tachycardia; deficiencies or dysregulation are linked to Parkinson’s disease, depression, and other conditions. Pharmacology targets catecholamine synthesis, receptors, reuptake, and degradation to treat these disorders.