The functional significance of the pentose phosphate pathway in synaptosomes: protection against peroxidative damage by catecholamines and oxidants.

Catecholamines added in vitro in rat brain synaptosomes activate the decarboxylation of glucose radioactively labelled on carbon 1, suggesting an effective activation of the pentose phosphate pathway. Stimulation also occurred with phenazine methosulphate, reduced glutathione and hydrogen peroxide. The activation of the pentose phosphate pathway by 5-hydroxytryptamine, noradrenaline and dopamine is ascribed to the activation of monoamine oxidase, producing both the respective biogenic aldehyde and hydrogen peroxide. Evidence is presented that the further metabolism of the aldehyde by aldehyde reductase and the removal of hydrogen peroxide by glutathione peroxidase both release the limitation of NADP+ availability for the pentose phosphate pathway by leading to the oxidation of NADPH. The relevance of the maintenance of reduced NADP+ on brain is discussed in relation to the metabolism of glutathione and to lipid peroxidation.