In cultured rat hepatocytes the key gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PCK) is known to be induced by glucagon via an elevation of cAMP. Prostaglandin E₂ has been shown to antagonize the glucagon-activated cAMP formation, glycogen phosphorylase activity and glucose output in hepatocytes. It was the purpose of the current investigation to study the potential of PGE₂ to inhibit the glucagon-induced expression of PCK on the level of mRNA and enzyme activity. PCK mRNA and enzyme activity were increased by 0.1 nM glucagon to a maximum after 2 h and 4 h, respectively. This increase was completely inhibited if 10 μM PGE2 was added concomitantly with glucagon. This inhibition by PGE₂ of glucagon-induced PCK activity was abolished by pertussis toxin treatment. When added at the maximum of PCK mRNA at 2 h, PGE₂ accelerated the decay of mRNA and reduced enzyme activity. This effect was not reversed by pertussis toxin treatment. Since in liver PGE₂ is derived from Kupffer cells, which play a key role in the local inflammatory response, the present data imply that during inflammation PGE₂ may reduce the hepatic gluconeogenic capacity via a Gᵢ-linked signal chain.

published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

Glucagon and insulin play important roles in controlling blood glucose and energy metabolism in vertebrate species. Recent studies have identified large cohorts of genes that could be regulated by glucagon and insulin. Signal transducer and activator of transcription (STAT) is a group of signal mediators/inducible transcription factors functionally coupled to class I cytokine receptors through JAK activation. Although the involvement of JAK/STAT pathway has been reported in the physiological actions of insulin and glucagon, the effects of these pancreatic hormones on STAT expression have not been examined. Using grass carp (Ctenopharyngodon idellus) as an animal model, we have cloned the cDNAs for STAT1, STAT3 and STAT5 and confirmed that they are single copy genes in the carp genome. Tissue expression profiling using RT-PCR revealed that the three members of STATs were ubiquitously expressed in various tissues of the grass carp including the liver. Function expression of grass carp STAT1, STAT3 and STAT5 in mammalian cell lines also demonstrated that the STAT proteins of fish origin were all effective in transactivating the target promoters with STAT-binding sites. In grass carp, hepatocyte culture, glucagon and insulin treatment were both effective in increasing STAT1, STAT3 and STAT5 mRNA expression. Using a pharmacological approach, the stimulatory effect of glucagon on transcripts expression of the three forms of STATs were shown to be mediated through activation of the cAMP/PKA, PI3K/AKT and MAPK ( Erk1/2 and JNK) pathways. In the case of insulin stimulation, the PI3K/AKT and p38 MAPK but not JNK pathways were involved in STAT1, STAT3 and STAT5 mRNA up-regulation. Furthermore, insulin-induced STAT3 and STAT5, but not STAT1 mRNA expression, could be blocked by Erk1/2 inactivation, suggesting that the MEK1/2/Erk1/2 pathway might be differentially coupled to gene expression of the individual members of STAT family. These findings provide evidence for first time that glucagon and insulin can regulate STAT1, STAT3 and STAT5 gene expression at the hepatic level in fish model via overlapping and yet distinct signaling mechanisms. / published_or_final_version / Biological Sciences / Master / Master of Philosophy

No description available.

Glucagon-like peptide-2 (GLP-2) augments intestinal adaptation in animal models of short bowel syndrome (SBS) and in adult patients with SBS. However, GLP-2 has not been used as a therapy for pediatric SBS. In this thesis, it is hypothesized that exogenous GLP-2 therapy will improve outcomes of intestinal adaptation in proximal intestinal resection (JI) and distal intestinal resection (JC) neonatal piglet models of SBS. Improvements in morphological parameters (increased small intestinal length) and histological parameters (increased jejunal villus length or jejunal crypt depth) of intestinal adaptation in JI and JC neonatal piglets treated with GLP-2 were observed. However, improved clinical outcomes (fewer days of diarrhea, fewer days on parenteral nutrition, more days on enteral nutrition alone) were only observed in GLP-2 treated JC animals. Since the JC anatomical subtype (no remnant ileum) represents the majority of clinical cases of neonatal SBS, these results support a potential role for GLP-2 therapy in pediatric SBS.

No description available.

Glucagon-like peptide-2 (GLP-2) augments intestinal adaptation in animal models of short bowel syndrome (SBS) and in adult patients with SBS. However, GLP-2 has not been used as a therapy for pediatric SBS. In this thesis, it is hypothesized that exogenous GLP-2 therapy will improve outcomes of intestinal adaptation in proximal intestinal resection (JI) and distal intestinal resection (JC) neonatal piglet models of SBS. Improvements in morphological parameters (increased small intestinal length) and histological parameters (increased jejunal villus length or jejunal crypt depth) of intestinal adaptation in JI and JC neonatal piglets treated with GLP-2 were observed. However, improved clinical outcomes (fewer days of diarrhea, fewer days on parenteral nutrition, more days on enteral nutrition alone) were only observed in GLP-2 treated JC animals. Since the JC anatomical subtype (no remnant ileum) represents the majority of clinical cases of neonatal SBS, these results support a potential role for GLP-2 therapy in pediatric SBS.

Impaired counterregulation during hypoglycemia in type 1 diabetes (T1D) is partly due to inadequate pancreatic islet alpha-cell glucagon secretion. We hypothesized that hypoglycemia can be prevented in autoimmune T1D by selective somatostatin receptor type 2 (SSTR2) antagonism of alpha cells to relieve SSTR2 inhibition, thereby increasing glucagon secretion. Diabetic biobreeding diabetes prone (BBDP) rats (D) vs non-diabetic BBDP (N) rats, underwent infusion of vehicle or SSTR2 antagonist (SSTR2a) during insulin-induced hypoglycaemia. D rats, treated with SSTR2a, needed little or no glucose to maintain hypoglycemia. To monitor real-time glucagon secretory response directly, we developed the technique of thin slices of the pancreas from D and N rats as well as normal human pancreas, subjected to perifusion with vehicle vs SSTR2a. SSTR2a treatment enhanced glucagon secretion in N and D rats and human pancreas. We conclude that SSTR2 antagonism can enhance hypoglycemia-stimulated glucagon release sufficient to achieve normoglycemic control.

Impaired counterregulation during hypoglycemia in type 1 diabetes (T1D) is partly due to inadequate pancreatic islet alpha-cell glucagon secretion. We hypothesized that hypoglycemia can be prevented in autoimmune T1D by selective somatostatin receptor type 2 (SSTR2) antagonism of alpha cells to relieve SSTR2 inhibition, thereby increasing glucagon secretion. Diabetic biobreeding diabetes prone (BBDP) rats (D) vs non-diabetic BBDP (N) rats, underwent infusion of vehicle or SSTR2 antagonist (SSTR2a) during insulin-induced hypoglycaemia. D rats, treated with SSTR2a, needed little or no glucose to maintain hypoglycemia. To monitor real-time glucagon secretory response directly, we developed the technique of thin slices of the pancreas from D and N rats as well as normal human pancreas, subjected to perifusion with vehicle vs SSTR2a. SSTR2a treatment enhanced glucagon secretion in N and D rats and human pancreas. We conclude that SSTR2 antagonism can enhance hypoglycemia-stimulated glucagon release sufficient to achieve normoglycemic control.

Thesis (Ph. D. in Molecular Physiology and Biophysics)--Vanderbilt University, May 2009. / Title from title screen. Includes bibliographical references.