QUANTITATIVE ASPECTS OF GLUTAMATE UTILIZATION BY RAT ADIPOSE TISSUE AND LIVER IN VITRO: EFFECT OF PERIODICITY OF EATING

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Abstract
The activity of two pathways supplying substrate for lipogenesis was enhanced in adipose tissue of meal-fed rats. One of these pathways, the forward pathway, involves the entry of α-ketoglutarate into the mitochondria, and metabolism via the Krebs cycle; the second pathway involves the backward flow of α-ketoglutarate to citrate in the cytoplasm, and cleavage of citrate to supply acetyl-CoA. Meal feeding increased fatty acid synthesis via the forward and backward pathways, but the relative amount of glutamate incorporated into lipid via the backward pathway decreased as a result of meal eating. The relative importance of the backward and forward pathways to the incorporation of α-ketoglutarate into fatty acid appeared to be similar for liver and adipose tissue. Lipogenesis from glutamate was significantly greater in adipose tissue incubated in bicarbonate than in phosphate buffer; however, the relative differences between tissues from meal-fed rats and from those fed ad libitum were similar in the two buffers. The possible importance of the backward pathway in the supply of precursors for fatty acid synthesis is discussed.