Medical Definition of norepinephrine
: a catecholamine C8H11NO3 that is the chemical means of transmission across synapses in postganglionic neurons of the sympathetic nervous system and in some parts of the central nervous system, is a vasopressor hormone of the adrenal medulla, and is a precursor of epinephrine in its major biosynthetic pathway—called also arterenol, noradrenaline; see levophed
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