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METABOLISM OF d‐[U‐14C]RIBOSE IN RAT TISSUES

Abstract— d‐[U‐14C]Ribose injected subcutaneously into the rat enters the blood, liver and brain. At 30 min after injection 40‐70 per cent of the radioactivity in the brain was found in amino acids and only 2‐6 per cent in free sugars. In contrast, free sugars (mainly glucose) and carboxylic acids accounted for most of the radioactivity in liver and blood. Evidence for the entry of [U‐14C]ribose into the brain was obtained by intracarotid or intravenous injection of [U‐14C]ribose after interrupting the blood supply to the liver and kidney. Under these conditions the radioactivity in the brain was found in amino acids, carboxylic acids and ribose; no significant amount of [14C]glucose was detected in brain or heart. It is concluded that ribose is metabolized directly in vivo in the brain. d‐[U‐14C]Ribose was metabolized also by brain slices in vitro to form 14C‐labelled amino acids and carboxylic acids; the rate was equivalent to the utilization of 0.65 μmol of ribose/g/h. The specific radioactivity of glutamine and of γ‐aminobutyrate was similar to or higher than that of glutamate in the brain. These results are discussed in the context of metabolic compartments.