Tissue Content of Citrate and Citrate-cleavage Enzyme Activity during Starvation and Refeeding

Abstract

IT is known that citrate, as well as being an intermediate of the tricarboxylic acid cycle, may also be involved in metabolic regulation because it increases the substrate affinity of acetyl-CoA carboxylase¹ and also acts as a direct inhibitor of phosphofructokinase^2,3. In view of the contradictory reports concerning the concentrations of rat liver citrate in different physiological conditions it is of interest to present data on the citrate concentrations of different rat tissues during starvation and refeeding with carbohydrate. The rats used were normal adult females weighing 200–300 g which had been raised on a standard diet (Instytut Leków, Warszawa). During the refeeding period animals were maintained on a high-glucose diet⁴. Rats were always decapitated at 12 o'clock. Pieces of liver and whole kidneys, heart and brain were rapidly removed, in this order, and placed in a mixture of carbon dioxide and ethanol. The frozen tissue was weighed and ground in a mortar, which was precooled, with 5 per cent trichloroacetic acid, and made up to volume for citrate analysis. Citrate was estimated according to McArdle⁵. Before determining the concentration of citric acid, samples were heated in a boiling water bath for 10 min.