Effects of Feeding States on Lipid Radioactivity in Liver, Muscle and Adipose Tissue after Injection of Labelled Glucose in the Rat

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Abstract

0.5 g of glucose/kg b.w. and (U-14C) glucose was injected i.v. to ad libitum fed, 18 hrs fasting or 48 hrs fasting-48 hrs refed rats. After 60 min blood glucose had decreased to preinjection values. Recirculation of radioactive metabolites was found in blood in pyruvate-lactate and to a small extent in glyceride-glycerol. Rats were sacrificed at this time and radioactivity measured in chloroform: methanol extracts of homogenates from muscle, liver and different adipose tissue regions. Furthermore, radioactivity was measured in fatty acids. Fatty acid radioactivity in different regions was considered to be due to the local synthesis of fatty acids, because no recirculation was discovered at the time of analysis. Liver and adipose tissue fatty acid synthesis was most pronounced in the refed rats. Adipose tissue showed higher fatty acid synthesizing activity than the liver in ad libitum fed, but not in refed rats. Glyceride-glycerol radioactivity was rather high in muscle. In adipose tissue it was more constant in different feeding states than fatty acid radioactivity was. By additions of measured radioactive metabolites glucose uptake in adipose tissue was roughly estimated to a few per cent of total glucose uptake.

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