Interrelationship of carbohydrate and fat metabolism in the involuting mammary gland

Abstract

The changes in the incorporation of 14C from [1-C14] glucose, [6-C14]glucose and [1-C14]acetate into C14O2 and C14-labelled lipid and in the activities of glucose 6-phosphate dehydrogenase and 6-phos-phogluconate dehydrogenase was studied at 19, 23, 28, 48 and 72 hours after the initiation of mammary-gland involution. The earliest change observed, at 19 hours was a decrease in the incorporation of C14 from [6-C14]-glucose and [1-Cl4]acetate into lipid and a stimulation in the formation of C14O2 from both these labelled substrates. This was followed at 23 hours by a depression in the formation of C14O2 from [1-C14] glucose and of glucose 6-phosphate-dehydrogenase activity, whereas 6-phosphogluconatedehydrogenase activity was unchanged and phosphoglucose-isomerase activity increased by about 34%. At 28 and 48 hours after the induction of involution the fall in the oxidation of C-1 of glucose was more marked, although this could be restored to the high value of the lactating gland by the addition of phenazine methosulphate (0.1 mM); the depression in fat synthesis was also striking. 6-Phosphogluconate-dehydrogenase activity decreased in involuting glands at these time-intervals. These results are discussed with reference to the time sequence of events and the interrelationship of carbohydrate and fat metabolism during mammary-gland involution.