catecholaminesdopamine

Catecholamines are a group of monoamine neurotransmitters and hormones derived from the amino acid tyrosine, characterized by a catechol group and an amine. The main peripheral catecholamines are norepinephrine and epinephrine, while dopamine is the primary catecholamine neurotransmitter in the brain and also a precursor to norepinephrine and epinephrine.

Biosynthesis begins with tyrosine, which is converted to L-DOPA by tyrosine hydroxylase, then to dopamine by aromatic L-amino acid decarboxylase. In neurons, dopamine is stored in vesicles; in adrenal chromaffin cells it is converted to norepinephrine by dopamine beta-hydroxylase, and norepinephrine can be further methylated to epinephrine by phenylethanolamine N-methyltransferase in the adrenal medulla and some CNS neurons.

Release and signaling occur when vesicles fuse with the presynaptic membrane in response to calcium. Dopamine acts on D1-D5 receptors, while norepinephrine and epinephrine act on adrenergic receptors (alpha and beta subtypes). Reuptake via transporters such as DAT and NET recycles these catecholamines, terminating signaling.

Metabolism involves monoamine oxidases (MAO-A and MAO-B) and catechol-O-methyltransferase (COMT), producing metabolites such as metanephrines and vanillylmandelic acid that can be measured clinically.

Physiological roles are diverse: dopamine regulates movement, reward, motivation, and cognition within the CNS; peripherally, catecholamines influence heart rate, vascular tone, and glucose metabolism. Clinically, dopamine dysfunction is linked to Parkinson disease and psychiatric conditions; therapies include L-DOPA for Parkinson disease, along with other agents that modify catecholamine signaling, reuptake, or breakdown.