Glyceroneogenesis and the supply of glycerol-3-phosphate for glyceride-glycerol synthesis in liver slices of fasted and diabetic rats.
The pathways of glycerol-3-phosphate (G3P) generation for glyceride synthesis were examined in precision-cut liver slices of fasted and diabetic rats. The incorporation of 5 mM [U-(14)C]glucose into glyceride-glycerol, used to evaluate G3P generation via glycolysis, was reduced by approximately 26-36% in liver slices of fasted and diabetic rats. The glycolytic flux was reduced by approximately 60% in both groups. The incorporation of 1.0 mM [2-(14)C]pyruvate into glyceride-glycerol (glyceroneogenesis) increased approximately 50% and approximately 36% in slices of fasted and diabetic rats, respectively, which also showed a two-fold increase in the activity phosphoenolpyruvate carboxykinase. The increased incorporation of 1.0 mM [2-(14)C]pyruvate into glyceride-glycerol by slices of fasted rats was not affected by the addition of 5 mM glucose to the incubation medium. The activity of glycerokinase and the incorporation of 1 mM [U-(14)C]glycerol into glyceride-glycerol, evaluators of G3P formation by direct glycerol phosphorylation, did not differ significantly from controls in slices of the two experimental groups. Rates of incorporation of 1 mM [2-(14)C]pyruvate and [U-(14)C]glycerol into glucose of incubation medium (gluconeogenesis) were approximately 140 and approximately 20% higher in fasted and diabetic slices than in control slices. It could be estimated that glyceroneogenesis by liver slices of fasted rats contributed with approximately 20% of G3P generated for glyceride-glycerol synthesis, the glycolytic pathway with approximately 5%, and direct phosphorylation of glycerol by glycerokinase with approximately 75%. Pyruvate contributed with 54% and glycerol with 46% of gluconeogenesis. The present data indicate that glyceroneogenesis has a significant participation in the generation of G3P needed for the increased glyceride-glycerol synthesis in liver during fasting and diabetes.
Martins-Santos
Maria Emilia Soares
ME
Department of Biochemistry and Immunology, School of Medicine, USP 14049-900 Ribeirão Preto, São Paulo, Brazil.
Chaves
Valéria Ernestânia
VE
Frasson
Danúbia
D
Boschini
Renata Polessi
RP
Garófalo
Maria Antonieta Rissato
MA
Kettelhut
Isis do Carmo
Ido C
Migliorini
Renato Hélios
RH
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002250:Carbon Radioisotopes; D003921:Diabetes Mellitus, Experimental / Q000201:enzymology / Q000378:metabolism*; D005508:Food Deprivation / Q000502:physiology; D005947:Glucose / Q000378:metabolism; D005989:Glycerides / Q000096:biosynthesis*; D005990:Glycerol / Q000378:metabolism; D005991:Glycerol Kinase / Q000378:metabolism; D005994:Glycerophosphates / Q000378:metabolism*; D066298:In Vitro Techniques; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D019764:Phosphoenolpyruvate Carboxykinase (ATP) / Q000378:metabolism; D019289:Pyruvic Acid / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014280:Triglycerides / Q000378:metabolism
D002250:Carbon Radioisotopes; D005989:Glycerides; D005994:Glycerophosphates; D014280:Triglycerides; D019289:Pyruvic Acid; D000255:Adenosine Triphosphate; C029620:alpha-glycerophosphoric acid; D005991:Glycerol Kinase; D019764:Phosphoenolpyruvate Carboxykinase (ATP); D005947:Glucose; D005990:Glycerol