Influence of starvation/refeeding transition on lipogenesis and NADPH producing systems in adipose tissue, mammary gland and liver at mid-lactation.

Glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and malic enzyme are enzymes involved in NADPH synthesis. Their specific activities and glucose utilization by isolated cell systems have been measured in adipose tissue and mammary gland from mid-lactating rats during starvation/refeeding transition. Starvation for 24 h produced a 75-90% decrease in the specific activities of these NADPH producing systems in mammary gland.

Effect of prolactin and glucocorticoids on P-enolpyruvate carboxykinase activity in liver and mammary gland from diabetic and lactating rats.

The administration of 2 bromo-alpha-ergocryptine, to reduce serum prolactin decreased the activity of cytosolic P-enolpyruvate carboxykinase (GTP) (EC 4.1.1.

Fatty acyl-CoAs as feedback regulators of hexose monophosphate shunt in rat adipocytes.

The high basal glucose utilization through hexose monophosphate shunt found in our experimental conditions were almost completely inhibited by oleate, octanoate and caproate. However, the inhibition of glucose oxidation due to butyrate was about 50% whereas ketone bodies and acetate did not inhibit. The rate of triacylglycerol formation was not significantly modified with the above organic acids except oleate that presented a 5-fold increase on labeling incorporation into lipids.

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.

Presence of cytosolic phosphoenolpyruvate carboxykinase activity in rat mammary gland.

The cytosolic P-enolpyruvate carboxykinase activity was measured in mammary gland and liver of animals at all stages of the reproductive cycle. The specific activity of this enzyme was almost absent in the mammary gland of virgin rats. Different pattern of P-enolpyruvate carboxykinase activity was obtained in liver and mammary gland during lactation cycle.