An investigation of the action of tyramine and its interrelationship with the effects of other sympathomimetic amines.

Choline 2,6-xylyl ether potentiated the sympathomimetic effects of tyramine and adrenaline in anaesthetized and spinal cats; the effects of noradrenaline were not significantly affected. The pressor activity of tyramine was also potentiated by the drug in reserpine-treated spinal cats and in pithed rats. The acute intravenous injection of reserpine in pithed rats potentiated pressor responses to tyramine, but depressed those to adrenaline and noradrenaline. During the intravenous infusion of noradrenaline in spinal cats and pithed rats the pressor responses to tyramine were increased, whilst those to adrenaline and noradrenaline were decreased. Infusion of isoprenaline in a spinal cat depressed responses to tyramine and noradrenaline, but potentiated those to adrenaline. A lower rate of infusion of isoprenaline in the same animal subsequently potentiated adrenaline and noradrenaline, but continued to depress tyramine. These results are held to be inconsistent with the view that the sympathomimetic effects of tyramine are produced entirely by the release of catechol amines.