Noradrenaline content of the heart of the adrenal-demedullated rat.

1. The noradrenaline (NA) concentration in the "heart" (atria and right ventricle) of male rats was estimated at different periods following adrenal demedullation. For 1-3 weeks after the operation there was, in all rats, a reduction in NA content of the tissue, whereas, after somewhat longer intervals, the concentrations had returned to normal in some but not in all animals, so that the range of values was very wide.2. In order to be able to test the effect of 2-aminotetralin on the cardiac NA of animals deprived of their medulla but having normal initial NA concentrations, an interval of 6-8 months was allowed to elapse between operation and injection of the drug; at this time the effect of the drug on cardiac NA was the same in intact and demedullated animals. There is thus no reason to attribute to the adrenal medulla any supporting role in the resynthesis of cardiac NA during periods of increased sympathetic activity.3. The time course of the pronounced fall in cardiac NA after adrenal demedullation resembles the time course of sodium retention shown by Gaunt, Renzi, Gisoldi & Howie (1967) to follow this operation. It is therefore suggested that it is the change in electrolyte metabolism which is responsible for the abnormality of NA storage; both phenomena occur in demedullated but not in adrenalectomized animals.