Experiments with highly tissue slices

In addition to perfusion experiments, tests with tissue slices have been cited to prove the conversion of fat to carbohydrate. Here, both changes in composition of the slices and their R. Q. have been determined and certain deductions drawn from these values. When these slices are prepared from well-fed animals, the levels of R. Q. are usually from 0.75 to 0.85, which can hardly support the hypothesis that a conversion of fat to sugar is occurring. However, when the liver slices are obtained from rats in which the carbohydrate stores are depleted, either by fasting or by a previous high-fat diet, figures for the respiratory quotient below 0.70 have been reported - while Dickens and Simer found values below 0.70 only when the tests were carried out with phosphate or bi-... 

In recent years a number of in vitro experiments have been reported on a variety of plant materials—segments of oat coleoptiles, segments of barley root, cut-up spinach leaves, discs of rhubarb leaves, slices of potato tubers —which demonstrate the utilization of di-and tricarboxylic acids by respiring cells and an increased rate of oxidation on addition of these substances they demonstrate further that malonate inhibits plant respiration. The stimulating effect of the substrates is often absent in fresh material, which is saturated with oxidizable substrates, but it is marked after storage, which depletes the tissue of substrates. The malonate inhibition is usually found only when the medium is acid (pH 5 or below) and when the concentration of malonate is relatively high (0.01 M and above). To obtain the same effects as in animal tissues ten- to a hundredfold concentrations of malonate are required. 

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