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Modern, fast-sweep electrochemical techniques have been applied to the study of the oxidation pathways of catecholamines in vitro. These techniques allow positive identifications of the transient intermediates, i.e., the open-chain o-quinones, and precise determinations of the rate of intramolecular cyclization to the substituted indole and its subsequent oxidation to the aminochrome. Significant differences in the rates of cyclization of adrenaline and noradrenaline are consistent with recent findings on the reactions of these catecholamines.Although the hormonal actions and other functions ax of the catecholamines have been studied extensively, detailed information regarding their reactions at the molecular level is still uncertain. It is well established that the major metabolic pathway of adrenaline and noradrenaline is via O methylation.2•3 However, due to the ease of oxidation of the catechol moiety at physiological pH, oxidative pathways of action cannot be dismissed entirely. Indeed, recent studies in vitro have shown that oxidative reactions of catecholamines are involved in various enzymatic and nonenzymatic processes.4-8 The present study was undertaken to learn more about the chemical reactions which are coupled with oxidative electron transfer in the catecholamines. Experimental SectionMaterials. 1-Adrenaline and adrenochrome were obtained from Sigma Chemical Co., dopamine came from Calbiochem. /-Noradrenaline ¿-bitartrate monohydrate and ¿/-a-methylnoradrenaline hydrochloride were kindly supplied by Dr. S. Archer of Sterling-Winthrop. ¿/-Isoproterenol sulfate dihydrate was that

The possibility that catecholamines can be oxidized via aberrant pathways in vivo is open to question, but in vitro oxidation via aerobic manipulations is established. Assuming oxidation does occur, we have examined quantitatively the fast chemical reactions of the initial oxidation products, the o-quinones. The nature and rates of these reactions were studies under the conditions simulating closely those which presumably exist in mammalian brain. The results are in close accord with existing literature and especially support oxidation pathways recently reported in [3H]-norepinephrine binding to particulate cell fractions.

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