SEPSIS-INDUCED ATTENUATION OF GLUCAGON AND 8-BRCAMP MODULATION OF THE PHOSPHOENOLPYRUVATE CARBOXYKINASE GENE

Sepsis is associated with alterations in hepatic gluconeogenesis. We have previously demonstrated that this change is associated with reduced expression of the phosphoenolpyruvate carboxykinase (PEPCK) gene, despite an endogenous hormonal milieu that should favor increased expression of the gene. To further elucidate the mechanisms involved, we induced sepsis in fasted Sprague-Dawley rats via cecal Ligation and single puncture, with sham-operated animals serving as controls, and we performed two sets of experiments. First, Liver tissue was obtained from septic and sham-operated animals at 2, 6, 16, and 24 h after the induction of sepsis. Northern blot hybridization analysis revealed a progressive, sepsis-induced decrease in expression of PEPCK and an increase in the expression of beta-fibrinogen, an acute-phase reactant. In the second set of experiments, we tested whether this reduced expression resulted from an attenuated response to 1) glucagon and 2) 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP). Twenty-four hours after the induction of sepsis, the liver was isolated and perfused with either Krebs buffer with substrate only (unstimulated controls), Krebs buffer + substrate + 10(-8) M glucagon, or Krebs buffer + substrate + 10(-5) M 8-BrcAMP. In sham-operated animals, perfusion with glucagon increased PEPCK mRNA levels and activity, whereas perfusion with buffer alone did not change mRNA levels and decreased activity. Glucagon perfusion of septic livers did not change either PEPCK mRNA levels or activity. Perfusion of sham-operated animals with 8-BrcAMP increased PEPCK mRNA levels and activity, whereas perfusion with buffer alone resulted in a decrease in mRNA levels and activity. Perfusion of septic Livers with 8-BrcAMP did not-change PEPCK mRNA. levels or activity. We conclude that sepsis induced by cecal ligation and puncture results in a time-dependent decrease in PEPCK mRNA levels that is not the result of a global depression in hepatic gene expression and that sepsis renders the PEPCK gene unresponsive to glucagon and 8-BrcAMP. These findings imply that the mechanism underlying the sepsis-induced defect in PEPCK gene expression involves factors distal to glucagon-stimulated cAMP production.