Abstract

The chief points in the present concept of the adrenergic nerve mediators may be briefly summarized as follows: 1. Convincing evidence has been produced to show that l-noradrenaline is the chief adrenergic nerve mediator in mammals. In addition i-adrenaline occurs admixed in various small amounts with the noradrenaline. The hypothesis of purelyexcitatory or purely inhibitory sympathins is no longer tenable. The liberation of other related substances such as hydroxytyramine, tyramine and oxidation products of dihydroxyphenyl derivatives in adrenergic nerve activity has not been proven in mammals. 2. The adrenergic nerve mediators l-noradrenaline and i-adrenaline can account for most actions observed on stimulation of adrenergic nerves. 3. Noradrenaline and adrenaline are formed in the adrenergic neurons and appear in small quantities in the nerve trunks and in larger amounts in the innervated organs, presumably occurring in the terminal nerve structures. 4. The adrenergic nerve mediators disappear from an organ after degeneration of the nerves but reappear on nerve regeneration. 5. There is some evidence in favour of the formation of noradrenaline by decarboxylation of dihydroxyphenylalanine and subsequent introduction of a hydroxyl group in the side chain of the hydroxytyramine so formed. 6. The adrenergic nerve mediators are rapidly inactivated in the tissues by enzymes (amine oxydase and catechol oxidase). A smaller part is excreted in free or conjugated form in the urine. 7. The physiological actions of noradrenaline and adrenaline differ in many important respects. The main function of noradrenaline seems to be the normal control of the circulation, while adrenaline produces various effects in conditions of stress and emergency.