A hypothesis concerning the effect of cocaine on the action of sympathomimetic amines.

There is a store, perhaps in chromaffin tissue, of noradrenaline in tissues with a sympathetic innervation. The store is depleted by treatment with reserpine. Sympathomimetic amines like tyramine act only when this store is present and have no effect when the store is depleted. They also fail to act in the presence of cocaine. Catecholamines like noradrenaline have a much greater action than usual when the store is depleted, and they have a much greater action in the presence of cocaine. It is suggested that cocaine has the effect of blocking release from the store, so that the action of tyramine is abolished and the spontaneous release from the store which is responsible for the normal (low) sensitivity to noradrenaline is stopped. Noradrenaline is taken up into the store in the heart and the vessel wall from the blood, and the disappearance of noradrenaline from the blood is in part due to this uptake and not entirely to destruction. Cocaine may prevent this uptake of noradrenaline by the tissue stores. Experiments on rabbit atria, on the vessels of the rabbit ear and on the heart-lung preparation are described which are consistent with this hypothesis.