Catecholamines and sympathomimetic agents have seven broad types of actions in the body: 1) excitatory effects on smooth muscle and glands, 2) inhibitory effects on smooth muscle, 3) excitatory effects on the heart, 4) metabolic effects, 5) endocrine effects, 6) central nervous system effects, and 7) effects on neurotransmitter release. The three most important catecholamines are norepinephrine, epinephrine, and dopamine. Norepinephrine is a neurotransmitter released by sympathetic nerves, epinephrine is a hormone from the adrenal medulla, and dopamine is a precursor to norepinephrine and epinephrine. Catecholamines exert their