INTERACTION OF LEUCINE, GLUCOSE, AND KETONE METABOLISM IN RAT BRAIN IN VITRO

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Abstract
Brain cortex slices from fed, 48 h and 120 h fasted rats were incubated and 14CO2 was measured from (a) [U‐14C]glucose (5 mm) either alone or in the presence of l‐lcucine (0.1 or 1 mm), and (b) [U‐14C]leucine or [l‐14C]leucine at 0.1 or 1 mm with or without glucose (5 mm). In other experiments, sodium dl‐3‐hydroxybutyrate (3‐OHB) or acetoacetate (AcAc) at 1 or 5 mm were added in the above incubation mixture. The rate of conversion of [U14C]glucose to CO2 was decreased 20% by leucine at 1 mm and 30–50% by 3‐OHB at 1 or 5 mm but not by leucine at 0.1 mm. The effects of 3‐OHB and of leucine (1 mm) were not additive. The effects of leucine were similar in the fed and fasted rats. The rate of conversion of [U‐14C]leucine or [l‐,4C]leucine to 14CO2 at 0.1 mm and 1.0 mm was increased by glucose (35%) in the fed or fasted rats. Ketone bodies in the absence of glucose had no effect on leucine oxidation. However, the stimulatory effect of glucose on the rate of conversion of leucine to CO2 was inhibited by 3‐OHB at 5 mm. These results suggest that (a) leucine in increased concentrations (1 mm) may reduce glucose oxidation by brain cortex while itself becoming an oxidative fuel for brain, and (b) leucine oxidation by brain may be influenced by the prevailing glucose and ketone concentrations.

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