The regulation of hepatic carbon flux by pyruvate dehydrogenase and pyruvate dehydrogenase kinase during long-term food restriction.
The present study investigated the effects of chronic food restriction (achieved by limiting access to food to 2 h daily for up to 8 weeks) on the activity of the active form of pyruvate dehydrogenase (PDHa) in liver. Accelerated and exaggerated activation of hepatic PDH in response to a meal, previously demonstrated to occur within 10 days of food restriction, was demonstrated to persist for 4 and 8 weeks of food restriction, despite a food intake of only 50-60% of controls. Activation of hepatic PDH during feeding in rats subjected to food restriction for 4 weeks was dependent on continued food intake. As a consequence, hepatic PDHa activities in food-restricted rats were suppressed relative to controls for 19 h of the 24 h daily cycle. Curve-fitting by second-order polynomial regression analysis demonstrated a significant positive correlation between hepatic PDHa activity and lipogenic rate over the range of PDHa activities observed during the 2 h feeding period. Increased lipogenesis during feeding in food-restricted rats was not at the expense of hepatic glycogen synthesis or deposition; measurement of concurrent rates of glycogenesis and lipogenesis revealed simultaneous flux through both pathways, but specific activation of lipogenesis. The accelerated re-activation of hepatic PDH observed within 1 h of feeding in rats subjected to 4 weeks of food restriction was facilitated by a failure of the 22 h interprandial fasting period to induce a stable increase in hepatic PDH kinase activity. The present study indicates differential regulation of hepatic PDH kinase activity during periods of food withdrawal between food-restricted rats and starved/re-fed control rats. Such regulation occupies a critical role in determining the rate of activation of hepatic PDH during feeding. In turn, increased activity of hepatic PDHa during feeding in food-restricted rats bears a close positive relationship with hepatic lipogenic rate.
Sugden
M C
MC
Department of Biochemistry, Faculty of Basic Medical Sciences, Queen Mary & Westfield College, University of London, U.K.
Grimshaw
R M
RM
Holness
M J
MJ
D000818:Animals; D004032:Diet; D004038:Diet, Reducing; D005260:Female; D008055:Lipids / Q000096:biosynthesis; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008112:Liver Glycogen / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012044:Regression Analysis; D013997:Time Factors
D008055:Lipids; D008112:Liver Glycogen; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D011768:Pyruvate Dehydrogenase Complex; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases