Abstract

The reviewed results show that the medullary granules are surrounded by a membrane which contains on its interior surface dopamine-β-hydroxylase. An active transport mechanism which is activated by ATP and magnesium and inhibited by reserpine catlyzes the uptake of catecholamines into the granules. Whether or not there exists also an active mechanism for the release of catecholamines is not yet settled. The results discussed favor the assumption that the granule membrane permits the release of catecholamines by diffusion. Our own experiments are in agreement with the hypothesis that the main part of the catecholamines is stored as a complex with ATP, bivalent ions, and a ribonucleoprotein or RNA.