MECHANISMS OF HORMONAL CONTROL OF GLUCONEOGENESIS

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It has been shown that sepsis changes the ability of certain hormones, such as insulin and glucagon, to modify gluconeogenesis. One particularly interesting aspect of this alteration is that sepsis impairs hormonal modulation of levels of the mRNA coding for phosphoenolpyruvate carboxykinase (PEPCK), the enzyme that catalyzes a rate limiting step in hepatic gluconeogenesis. The project outlined in this proposal centers on elucidation of the mechanisms by which glucagon-induced increases in the transcription of the PEPCK gene are altered by sepsis. One hypothesis is that sepsis causes a defect in the behavior of the signal transduction pathway which mediates the intracellular effects of glucagon. This pathway is known to involve several components; a membrane bound receptor, the guanine regulatory protein Gs, the enzyme adenylate cyclase, the intracellular second messenger cyclic adenosine monophosphate (cAMP) and (an) intracellular factor(s) which lead(s) to transcription of the PEPCK gene. We propose to investigate each of the first four components and the way in which they interact to determine if sepsis alters their behavior. This will be accomplished by a) measuring the activity of PEPCK, levels of PEPCK mRNA and rate of transcription of the PEPCK gene in livers isolated from septic or sham operated rats perfused with cAMP or forskolin (which stimulates adenylate clyclase), b) determining NaF-or PGE1-stimulated adenylate cyclase activity in membranes isolated from hepatocytes derived from septic or sham operated animals, c) determining levels of Gs by immunoblot analysis and d) comparing the number of hepatocyte glucagon receptors in septic and sham- operated animals.