Coordination of glucose metabolism and NADPH formation in the adipose tissue and mammary gland during the lactation-weaning transition.

The capacity of fat cells from 48-hour weaned mid-lactating rats to synthesize fatty acids from (1-14C)-glucose and (6-14C)-glucose was markedly increased compared to adipocytes isolated from mid-lactating rats kept with their pups. Pentose shunt activity and glycolytic flux were also markedly increased in fat cells from weaned mid-lactating rats. Isolated fat cells from mid-lactating weaned rats, incubated with oleate and substrates that potentially may supply triosephosphate, showed a significantly stimulated triglyceride synthesis as measured by (1-14C)-oleate incorporation into the acyl moiety. The specific activities of malic enzyme, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were measured in adipose tissue and mammary gland extracts during pregnancy, lactation and weaning. These enzyme activities in the mammary gland increased in parallel from the beginning of pregnancy to the end of lactation. After weaning there was a sharp decrease in enzyme activities to levels similar to those found in mammary glands from virgin rats. In contrast, the activities of the lipogenic enzymes in adipose tissue were very low during lactation but increased rapidly after weaning.