[Effect of sympathomimetic substances and DOPA on the ultrastructure of the nervous apparatus of the heart].

After a single administration of norepinephrine or DOPA to albino rats there occurred an incorporation of norepinephrine into the adrenergic axons of the heart and its deposition in the form of granules in small synaptic vesicles, about 300 A in diameter. The adrenergic and cholinergic axons can be thus differentiated. The amount of cholinergic axons in the auricles is greater than that of the adrenergic ones. The adrenergic terminals came into the most intimate contact with the cholinergic terminals and with the endothelial cells of the blood capillaries and the myocardial muscle cells. It is supposed that adrenergic fibers can act upon the heart muscle in three ways: by means of presynaptic inhibition through the cholinergic axons, by humoral route, and directly on the myocardial muscle cells.