The effect of L-3,4-dihydroxyphenylalanine administration on glucose metabolism in brain.

Abstract

AbstractThe effect of the administration of l‐3,4‐dihydroxyphenylalanine (l‐DOPA) on the metabolism of glucose in brain was studied by administering [U‐14C]glucose to three groups of rats: (1) those injected previously with l‐DOPA, 100 mg/kg; (2) those fed 1 % (w/w) l‐DOPA in their diet for several months and also injected 15 min before the administration of glucose with l‐DOPA, 100 mg/kg; and (3) appropriate controls. Chronic treatment with l‐DOPA caused a decrease in the flux of carbon from glucose in plasma to those amino acids in brain that are in equilibrium with the tricarboxylic acid cycle intermediates but not to lactate and alanine. Similar differences from controls, but of smaller magnitude, were observed in rats given a single injection of l‐DOPA. Concentrations of glucose in plasma and in brain were increased after acute or chronic treatment with l‐DOPA. A single injection of l‐DOPA did not cause changes in the levels of the most abundant amino acids in brain, but after chronic treatment with l‐DOPA modest changes were noted in the brain levels of some ninhydrin‐reacting substances; the contents of taurine and aspartate were lower and those of threonine, serine, glutamine, and glycine were higher.