catecholamine, any of several compounds occurring naturally in the body that serve as hormones or as neutrotransmitters in the sympathetic nervous system. The catecholamines include such compounds as epinephrine, or adrenaline, norepinephrine, and dopamine. They resemble one another chemically in having an aromatic portion (catechol) to which is attached an amine, or nitrogen-containing group. Epinephrine and norepinephrine, which are also hormones, are secreted by the adrenal medulla, and norepinephrine is also secreted by some nerve fibers. These substances prepare the body to meet emergencies such as cold, fatigue, and shock, and norepinephrine is probably a chemical transmitter at nerve synapses. Dopamine is an intermediate in the synthesis of epinephrine; in addition, a deficiency of dopamine in the brain is responsible for the symptoms of Parkinson's disease. Medical administration of the drug L-dopa, which is presumed to be converted to dopamine in the brain, relieves the symptoms. Epinephrine is used medically to stimulate heartbeat and to treat emphysema, bronchitis, and bronchial asthma and other allergic conditions, as well as in the treatment of the eye disease glaucoma.