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1. A hormone produced by the adrenal (suprarenal) medulla, similar in chemical and pharmacological properties to epinephrine but chiefly a vasoconstrictor with little effect on cardiac output.
2. A neurotransmitter released by most sympathetic postganglionic neurons and by some neurons of the brain. A disturbance in its metabolism at important brain sites has been implicated in affective disorders. It is used to manage severe hypotension, esp. in patients with neurogenic or septic shock.

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