Ammonia inhibits insulin stimulation of the Krebs cycle: further insight into mechanism of hepatic coma.
Oxidation of [2,3-14C]succinate in the intramitochondrial Krebs cycle was used as a probe to investigate the effect of ammonia on protein incorporation and Krebs cycle oxidation of succinate carbons in isolated rat hepatocytes. At low concentrations of ammonium chloride (0.1 to 0.5 mM) a slight increase in 14CO2 formation from [2,3-14C]succinate was observed, however, the stimulatory effect of insulin was significantly reduced. Insulin failed to cause any stimulation of succinate carbons incorporation into hepatocyte protein in the presence of ammonium chloride. Addition of ammonium chloride also depressed the movement of tracer carbons into the gluconeogenesis pathway. The activity of the amphibolic amino acid pool was significantly enhanced by ammonia. The data presented in this paper lend strong support to the Krebs-cycle depletion theory of hepatic coma. They also suggest that reduced mitochondrial Krebs cycle activity caused by increased amphibolic depletion of substrates results in loss of insulin sensitivity in ammonia toxicity.
Bessman
S P
SP
Department of Pharmacology and Nutrition, University of Southern California, School of Medicine, Los Angeles 90033.
Wang
W
W
Mohan
C
C
D000643:Ammonium Chloride / Q000494:pharmacology*; D000818:Animals; D002250:Carbon Radioisotopes; D002478:Cells, Cultured; D002952:Citric Acid Cycle / Q000187:drug effects*; D005971:Glutamates / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D007329:Insulin Antagonists / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008297:Male; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D014176:Protein Biosynthesis; D051381:Rats; D011919:Rats, Inbred Strains; D013386:Succinates / Q000378:metabolism
D002250:Carbon Radioisotopes; D005971:Glutamates; D007328:Insulin; D007329:Insulin Antagonists; D013386:Succinates; D000643:Ammonium Chloride