Phenobarbital reduces blood glucose and gluconeogenesis through down-regulation of phosphoenolpyruvate carboxykinase (GTP) gene expression in rats.
The regulatory mechanism of phosphoenolpyruvate carboykinase (GTP) (EC 4.1.1.32) (PEPCK) gene expression and gluconeogenesis by phenobarbital (PB), which is known to induce drug-metabolizing enzymes, was investigated. Higher level of PEPCK mRNA was observed in spherical rat primary hepatocytes on EHS-gel than monolayer hepatocytes on TIC (type I collagen). We found that PB directly suppressed PEPCK gene expression in spherical hepatocytes on EHS-gel, but not in those on TIC. PB strongly suppressed cAMP-dependent induction of PEPCK gene expression. Tyrosine aminotransferase (TAT), another gluconeogenic enzyme, was induced by cAMP, but not suppressed by PB. Chronic administration of PB reduced hepatic PEPCK mRNA in streptozotocin-induced diabetic and nondiabetic rats, and PB reduced blood glucose level in diabetic rats. Increased TAT mRNA in diabetic rats was not suppressed by PB. These results indicated that PB-dependent reduction is specific to PEPCK. From pyrvate challenge test, PB suppressed the increased gluconeogenesis in diabetic rats. PEPCK gene promoter activity was suppressed by PB in HepG2 cells. In conclusion, we found that spherical hepatocytes cultured on EHS-gel are capable to respond to PB to suppress PEPCK gene expression. Moreover, our results indicate that hypoglycemic action of PB result from transcriptional repression of PEPCK gene and subsequent suppression of gluconeogenesis.
Laboratory of Nutritional Biochemistry, Department of Applied Molecular Biosciences, Nagoya University, Nagoya 464-8601, Japan. Electronic address: hirooda@agr.nagoya-u.ac.jp.
Hiroaki
H
Oda
Laboratory of Nutritional Biochemistry, Department of Applied Molecular Biosciences, Nagoya University, Nagoya 464-8601, Japan.
Yuji
Y
Okuda
Laboratory of Nutritional Biochemistry, Department of Applied Molecular Biosciences, Nagoya University, Nagoya 464-8601, Japan.
Yukiko
Y
Yoshida
Laboratory of Nutritional Biochemistry, Department of Applied Molecular Biosciences, Nagoya University, Nagoya 464-8601, Japan.
Noriko
N
Kimura
Laboratory of Nutritional Biochemistry, Department of Applied Molecular Biosciences, Nagoya University, Nagoya 464-8601, Japan.
Atsushi
A
Kakinuma
D000818:Animals; D001786:Blood Glucose / Q000187:drug effects / Q000502:physiology*; D003921:Diabetes Mellitus, Experimental; D015536:Down-Regulation; D020869:Gene Expression Profiling; D015971:Gene Expression Regulation, Enzymologic; D005943:Gluconeogenesis / Q000187:drug effects / Q000502:physiology*; D005947:Glucose / Q000378:metabolism; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000166:cytology / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D007328:Insulin / Q000378:metabolism; D008297:Male; D010634:Phenobarbital / Q000494:pharmacology*; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D001786:Blood Glucose; D007328:Insulin; D010729:Phosphoenolpyruvate Carboxykinase (GTP); D005947:Glucose; D010634:Phenobarbital
Blood glucose; Diabetes; Hepatocyte; PEPCK; Phenobarbital; Pyruvate challenge