Studies on the metabolism of mammary tissue in vitro. 1. Oxidation of acetate and glucose by slices of lactating rat mammary gland

Abstract

By the use of doubly labeled sodium acetate (C14H3. C13O2Na) and of glucose labeled uniformly and in the C-1 atom, the rates of oxidation of acetate and glucose C by lactating-rat mammary slices were measured in the presence and absence of other substances. The ratio of the rates of oxidation of the acetate C atoms is increased by the addition of either glucose or pyruvate; glucose also depresses the total rate of oxidation of acetate while pyruvate does not. The formula of Strisower et al. (1952), which accounts for a change in the ratio of the rates of oxida-tion of the acetate carbon atoms in terms of isotope dilution in the tri-carboxylic acid cycle, was applied to these results, and certain dis-crepancies observed. These might be due to competition for diphos-phopyridine nucleotide (DPN). This possibility was tested using added DPN and nicotinamide. A comparison of the relative rates of oxidation of the C-l atom of glucose and the methyl atom of acetate indicated that most of the C-l atoms must be catabolized by a route other than glycolysis, probably the direct oxidative pathway. If the direct oxida-tive pathway is quantitatively important in this tissue the depressing effect of pyruvate on the rate of oxidation of the C-l atom of glucose is anomalous. Possible reasons for the effect are discussed.