Studies of the long-term regulation of hepatic pyruvate dehydrogenase kinase.
The administration of a low-carbohydrate/high-saturated-fat (LC/HF) diet for 28 days or starvation for 48 h both increased pyruvate dehydrogenase kinase (PDHK) activity in extracts of rat hepatic mitochondria, by approx. 2.1-fold and 3.5-fold respectively. ELISAs of extracts of hepatic mitochondria, conducted over a range of pyruvate dehydrogenase (PDH) activities, revealed that mitochondrial immunoreactive PDHKII (the major PDHK isoform in rat liver) was significantly increased by approx. 1.4-fold after 28 days of LC/HF feeding and by approx. 2-fold after 48 h of starvation. The effect of LC/HF feeding to increase hepatic PDHK activity was retained through hepatocyte preparation, but was decreased on 21 h culture with insulin (100 micro-i.u./ml). A sustained (24 h) 2-4-fold elevation in plasma insulin concentration in vivo (achieved by insulin infusion via an osmotic pump) suppressed the effect of LC/HF feeding so that hepatic PDHK activities did not differ significantly from those of (insulin-infused) control rats. The increase in hepatic PDHK activity evoked by 28 days of LC/HF feeding was prevented and reversed (within 24 h) by the replacement of 7% of the dietary lipid with long-chain omega-3 fatty acids. Analysis of hepatic membrane lipid revealed a 1.9-fold increase in the ratio of total polyunsaturated omega-3 fatty acids to total mono-unsaturated fatty acids. The results indicate that the increased hepatic PDHK activities observed in livers of LC/HF-fed or 48 h-starved rats are associated with long-term actions to increase hepatic PDHKII concentrations. The long-term regulation of hepatic PDHK by LC/HF feeding might be achieved through an impaired action of insulin to suppress PDHK activity. In addition, the fatty acid composition of the diet, rather than the fat content, is a key influence.
Sugden
M C
MC
Department of Biochemistry, Basic Medical Sciences, St. Bartholomew's and the Royal London School of Medicine and Dentistry, Queen Mary and Westfield College, Mile End Road, London E1 4NS, U.K.
Fryer
L G
LG
Orfali
K A
KA
Priestman
D A
DA
Donald
E
E
Holness
M J
MJ
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002210:Caprylates / Q000494:pharmacology; D002478:Cells, Cultured; D004032:Diet; D004041:Dietary Fats / Q000008:administration & dosage; D004797:Enzyme-Linked Immunosorbent Assay; D015525:Fatty Acids, Omega-3 / Q000008:administration & dosage; D005260:Female; D007328:Insulin / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism; D008099:Liver / Q000166:cytology; D008563:Membrane Lipids / Q000032:analysis; D008930:Mitochondria, Liver / Q000201:enzymology*; 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; D013217:Starvation
D002210:Caprylates; D004041:Dietary Fats; D015525:Fatty Acids, Omega-3; D007328:Insulin; D007527:Isoenzymes; D008563:Membrane Lipids; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D011768:Pyruvate Dehydrogenase Complex; D003994:Bucladesine; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases