Renal gluconeogenesis. The effect of diet on the gluconeogenic capacity of rat-kidney-cortex slices

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Abstract
The optimum conditions for the conversion of lactate, pyruvate, intermediates of the tricarboxylic acid cycle and amino acids into glucose in rat-kidney-cortex slices have been investigated. The balanced saline medium of Krebs and Henseleit (1932) was found to give maximal values. The rates of gluconeogenesis were much higher than those observed by previous investigators. Pyruvate yielded up to 450 [mu]moles of glucose/g. dry wt./hr. Reduction of the concentrations of HCO3, CO2 or Mg2+ ions, or increasing the concentration of phosphate to 8 mM, had no major effects on the rates of gluconeogenesis from lactate or fumarate, but omission of Ca2+ ions reduced the rate by about 70%. By keeping rats for 3-5 days on a diet low in carbohydrate the capacity of the tissue to synthesize glucose from various precursors was almost doubled. Starvation (for 48 hours) also increased the gluconeogenic capacity, but not as much as the low-carbohydrate diet. Of the gluconeogenic amino acids only glutamate, aspartate, proline, ornithine and arginine yielded glucose rapidly. An enzymic method for the determination of glycogen is described. Several advantages of kidney cortex over liver as a material for the study of gluconeogenesis are pointed out; a major one is the low content of preformed carbohydrate.