cyclic-gmp and fructose-1-6-diphosphate

Fructose 1,6-P2 (F1,6BP) protects rat liver against experimental hepatitis induced by galactosamine (GalN) by means of two parallel effects: prevention of inflammation, and reduction of hepatocyte sensitization to tumour necrosis factor-alpha (TNF-alpha). In a previous paper we reported the underlying mechanism involved in the prevention of inflammation. In the present study, we examined the intracellular mechanisms involved in the F1,6BP inhibition of the apoptosis induced by TNF-alpha in parenchyma cells of GalN-sensitized rat liver. We hypothesized that the increased nitric oxide (NO) production in livers of F1,6BP-treated rats mediates the antiapoptotic effect. This hypothesis was evaluated in cultured primary rat hepatocytes challenged by GalN plus tumour necrosis factor-alpha (GalN+TNF-alpha), to reproduce in vitro the injury associated with experimental hepatitis. Our results show a reduction in apoptosis concomitant with an increase in NO production and with a reduction in oxidative stress. In such conditions, guanylyl cyclase is activated and the increase in cGMP reduces the TNF-alpha-induced apoptosis in hepatocytes. These results provide new insights in the protective mechanism activated by F1,6BP and confirm its interest as a hepatoprotective agent.

Topics: Animals; Apoptosis; Cells, Cultured; Culture Media, Serum-Free; Cyclic GMP; Dose-Response Relationship, Drug; Fructosediphosphates; Galactosamine; Hepatocytes; Male; Nitric Oxide; Rats; Rats, Sprague-Dawley; Time Factors; Tumor Necrosis Factor-alpha

Working rat hearts perfused with 5.5 mM glucose were submitted to a 10-min period of no-flow ischaemia or anoxia. Both conditions stimulated glycogenolysis, activated phosphorylase and increased cyclic GMP content, although the time course of these changes differed in anoxia and ischaemia. Changes in cyclic GMP content were not correlated with glycogenolysis or phosphorylase activation. Perfusion with 1 microM L-nitroarginine methylester, an inhibitor of nitric oxide synthase, decreased cGMP concentration under normoxic conditions and abolished the ischaemia-induced increase in cGMP. The inhibitor decreased the coronary flow without affecting the overall working performance of the hearts under normoxic conditions.

Topics: Adenosine Triphosphate; Amino Acid Oxidoreductases; Animals; Arginine; Coronary Circulation; Cyclic GMP; Fructosediphosphates; Glucose; Glycogen; Heart; Hexosephosphates; Hypoxia; In Vitro Techniques; Kinetics; Male; Myocardial Ischemia; Myocardium; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Perfusion; Rats; Rats, Wistar; Time Factors

The effects of the dibutyryl derivatives of cyclic GMP and cyclic AMP on lactic acid and steroid production were compared in intact mouse adrenal glands at concentrations of 0.5-1 mmol/l and in mouse adrenal cell suspensions at concentrations of 0.01-1 mmol/l. The dibutyryl derivative of cyclic GMP had little or no effect on lactic acid production in either tissue preparation. It caused a slight stimulation of corticosteroid output in intact glands at a concentration of 1 mmol/l, amounting to one-tenth of the response observed with 1 mM-dibutyryl cyclic AMP. Dose-dependent increases in lactic acid and steroid production were obtained with dibutyryl cyclic AMP in cell suspensions. AMP and GMP increased lactic acid but not steroid production. All the substrates tested (glucose, glucose-6-phosphate, fructose, fructose-6-phosphate, fructose-1,6-diphosphate, 10 mmol/l; pyruvate and glycerol, 20 mmol/l) stimulated basal glycolysis in intact glands and cell suspensions and none affected basal steroid production significantly. By far the greatest increase in lactic acid production was noted with fructose-1,6-diphosphate. However, only glucose and, in unsectioned glands, pyruvate exerted a potentiating effect on the glycolytic response to ACTH. Glucose potentiated the steroidogenic response to ACTH also, but only in intact glands. The relative ineffectiveness of dibutyryl cyclic GMP is in accord with the species-dependent differing responses to the free form of the cyclic nucleotides noted in mouse and rat adrenal glands. The substrate requirements are in keeping with a rate-limiting role of phosphofructokinase and an action of ACTH at some site between the entry of glucose into the cell and the formation of fructose-1,6-diphosphate.

Topics: Adrenal Glands; Adrenocorticotropic Hormone; Animals; Bucladesine; Corticosterone; Cyclic GMP; Dibutyryl Cyclic GMP; Dose-Response Relationship, Drug; Fructosediphosphates; Glucose; Glycolysis; In Vitro Techniques; Lactates; Lactic Acid; Male; Mice; Mice, Inbred Strains; Pyruvates