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The substance diffusing into circulation from sympathetic nerve terminals when they are active. The term was introduced by WB Cannon, who thought that this substance differed from the mediator produced by the nerve ending (now known to be incorrect); the mediator itself (norepinephrine) diffuses into circulation.
Synonym(s): sympathetic hormone


An older, nonspecific term for:
(1) A catecholamine, in particular norepinephrine;
(2) A sympathetic neurotransmitter.

Sympathin is not used in the working medical parlance.
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