Metabolic Adaptations in Fatty Acid and Lactose Biosynthesis by Sheep Mammary Tissue During Cessation of Lactation

Abstract

The effect of involution of fatty acid synthesis, lactose synthesis, and carbon dioxide production by sheep mammary tissue was examined. Mammary tissue from lactating or nonlactating (9 days after weaning) sheep was used for measurements of biosynthetic capacities (in vitro incubations) and enzymatic activities. Termination of lactation decreased biosynthetic rates of fatty acid and lactose synthesis 99 and 97%. Similarly, rates of acetate and glucose oxidation to carbon dioxide by mammary tissue from nonlactating sheep relative to lactating sheep decreased 84 and 98%. Of enzymes in fatty acid synthesis, acetyl-CoA carboxylase decreased the most dramatically as a result of involution (99%). Other major decrease were for acetyl-CoA sythetase (79%) and fatty acid synthetase (85%) while enzymes involved in reducing equivalent generation (glucose-76-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and NADP-isocitrate dehydrogenase) decreased less dramatically. for enzymes in lactose synthesis, involution decreased UDP-glucose 4-epimerase (76%), UDP-glucose pyrophosphorylase (87%), and lactose synthetase (93%) while activity of phosphoglucomutase remained unchanged. With the termination of lactation, the magnitude of alterations in rates of fatty acid sythesis and lactose synthesis compared most closely to decreases in acetyl-CoA carboxylase activity and lactose synthetase activity, respectively.