The Mode of Action of Tyramine

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Abstract
The repeated administration of tyramine to the isolated perfused guinea-pig heart gradually decreased the positive inotropic response which was paralleled by a decrease in the noradrenaline content of the heart and an increase in the noradrenaline content of the perfusate. Phenethylamine, ephedrine, amphetamine, guanethidine and bretylium were administered to the isolated heart until no further positive inotropic effect was obtained. The absence of an inotropic response with phenethylamine and guanethidine was associated with a decrease in the noradrenaline content of the heart. The absence of an inotropic effect with amphetamine, bretylium and ephedrine was not associated with a decrease in the amount of noradrenaline in the heart.