any agent that causes a narrowing of an opening of a blood vessel: cold or stress or nicotine or epinephrine or norepinephrine or angiotensin or vasopressin or certain drugs; maintains or increases blood pressure

the secretion of an endocrine gland that is transmitted by the blood to the tissue on which it has a specific effect

a neurochemical that transmits nerve impulses across a synapse

any of a group of chemicals including epinephrine and norepinephrine that are produced in the medulla of the adrenal gland

any of a group of chemical compounds that contain both hydroxyl and amino functional groups on an alkane backbone.