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The involvement of glucocorticoids in regulating the activity of phosphatidate phosphohydrolase and the synthesis of triacylglycerols in the liver. Effects of feeding rats with glucose, sorbitol, fructose, glycerol and ethanol.

ABSTRACT: Feeding rats with sorbitol, fructose, glycerol and ethanol increases the concentration of serum corticosterone without significantly altering the concentration of insulin. This increase appears to be partly responsible for the increases in the hepatic activity of phosphatidate phosphohydrolase (compared with rats fed glucose or 0.9% NaCl) that has been reported [Sturton, Pritchard, Han & Brindley (1978) Biochem. J. 174, 667--670] and the enhanced capacity of the liver to synthesize triacylglycerols. The ethanol-induced increase in phosphohydrolase activity was largely, but not completely, prevented by adrenalectomy.

SUBMITTER: Brindley DN

PROVIDER: S-EPMC1161034 | biostudies-other | 1979 Apr

REPOSITORIES: biostudies-other

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Project description:Rat hepatocytes were incubated in monolayer culture in modified Leibovitz L-15 medium containing either 10% (v/v) newborn-calf serum or 0.2% (w/v) fatty-acid-poor bovine serum albumin. The addition of 100 nM-dexamethasone increased the activities of both phosphatidate phosphohydrolase and tyrosine aminotransferase by about 3.5-fold after 8h, and these activities continued to rise until at least 24h. Incubating the hepatocytes in the albumin-containing medium with 10 microM- or 100 microM-8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate increased the activities of the phosphohydrolase and aminotransferase by 2.6- and 3.4-fold respectively after 8h. These increases were blocked by actinomycin D. The increases in the activities that were produced by the cyclic AMP analogue and dexamethasone were independent and approximately additive. Insulin when added alone did not alter the phosphohydrolase activity, but it increased the aminotransferase activity by 34%. The dexamethasone-induced increase in the phosphohydrolase activity was completely blocked by 7-144 microM-insulin, whereas that of the aminotransferase was only partly suppressed. Insulin had no significant Effects on the increases in the activities of phosphatidate phosphohydrolase and tyrosine aminotransferase that were produced by the cyclic AMP analogue, but this may be because the analogue is fairly resistant to degradation by the phosphodiesterase. The activity of glycerol kinase was not significantly changed by incubating the hepatocytes with insulin, dexamethasone and the cyclic AMP analogue alone or in combinations. It is proposed that high concentrations of cyclic AMP and glucocorticoids increase the total activity of phosphatidate phosphohydrolase in the liver and provide it with an increased capacity for synthesizing triacylglycerols and very-low-density lipoproteins, which is expressed when the availability of fatty acids is high. There appears to be a co-ordinated hormonal control of triacyglycerol synthesis and gluconeogenesis in diabetes and in metabolic stress to enable the liver to supply other organs with energy.

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The involvement of glucocorticoids in regulating the activity of phosphatidate phosphohydrolase and the synthesis of triacylglycerols in the liver. Effects of feeding rats with glucose, sorbitol, fructose, glycerol and ethanol.

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