The effects of acetate and of pyruvate on the pathways of glucose catabolism in lactating mammary tissue: 1. Rat tissue

Summary A study was made of the changes in the pathways of glucose catabolism in slices of lactating rat mammary gland which occurred when acetate or pyruvate was added to the medium. When acetate was added there was an increase in the rates of oxidation of the C (2) and C (6) atoms of glucose but little change in that of the C (1) atom. The amounts of these carbon atoms which were incorporated into fatty acids, lactic acid and glyceride glycerol were reduced, but the results showed that the relative proportion of the glucose converted to these substances which passed through the pentose phosphate pathway was increased. When pyruvate was added, the rates of oxidation of the C (1) , C (2) and C (6) atoms were all reduced to about the same extent. The incorporation of the glucose carbon into fatty acids was almost abolished and its incorporation into lactic acid and glyceride glycerol was very much reduced. The results showed that most of the glucose incorporated into these compounds under these conditions passed through the pentose phosphate pathway. Evidence is presented which suggests that the triose phosphates are not in complete isotopic equilibrium in lactating rat mammary tissue. These results are discussed in relation to the existence of 2 pools of acetyl coenzyme A, one intra- and the other extra-mitochondrial, and to the possible inhibition of certain steps of the glycolytic pathway.