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an obsolete general name for a biologically active substance similar in structure to adrenaline. In vertebrates (including man), sympathins are secreted when impulses are transmitted from sympathetic nerves (hence the name) to the organ that performs a particular function. In early research on humoral regulation the sympathetic mediators of nervous excitation were called sympathins. Later it was established that the properties of a mediator are exhibited in the peripheral sections of the sympathetic nervous system by norepinephrine and in the central sections of dopamine. In amphibians sympathins have been identified as adrenaline.