scholarly journals Effects of cyclic AMP, glucocorticoids and insulin on the activities of phosphatidate phosphohydrolase, tyrosine aminotransferase and glycerol kinase in isolated rat hepatocytes in relation to the control of triacylglycerol synthesis and gluconeogenesis

1985 ◽  
Vol 227 (3) ◽  
pp. 1031-1031
Keyword(s):  
Cyclic Amp ◽  
Rat Hepatocytes ◽  
Tyrosine Aminotransferase ◽  
Glycerol Kinase ◽  
Isolated Rat Hepatocytes ◽  
Triacylglycerol Synthesis ◽  
Phosphatidate Phosphohydrolase ◽  
Isolated Rat

scholarly journals Effects of cyclic AMP, glucocorticoids and insulin on the activities of phosphatidate phosphohydrolase, tyrosine aminotransferase and glycerol kinase in isolated rat hepatocytes in relation to the control of triacylglycerol synthesis and gluconeogenesis

1985 ◽  
Vol 225 (2) ◽  
pp. 455-462 ◽  
Author(s):  
R A Pittner ◽  
R Fears ◽  
D N Brindley
Keyword(s):  
Cyclic Amp ◽  
Calf Serum ◽  
Rat Hepatocytes ◽  
Tyrosine Aminotransferase ◽  
Glycerol Kinase ◽  
Hormonal Control ◽  
Very Low Density Lipoproteins ◽  
Isolated Rat Hepatocytes ◽  
Triacylglycerol Synthesis ◽  
Phosphatidate Phosphohydrolase

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.

scholarly journals Oleic acid promotes the activation and translocation of phosphatidate phosphohydrolase from the cytosol to particulate fractions of isolated rat hepatocytes

1984 ◽  
Vol 219 (3) ◽  
pp. 911-916 ◽  
Author(s):  
C Cascales ◽  
E H Mangiapane ◽  
D N Brindley
Keyword(s):  
Fatty Acids ◽  
Endoplasmic Reticulum ◽  
Oleic Acid ◽  
Microsomal Fraction ◽  
Rat Hepatocytes ◽  
Total Activity ◽  
Cell Fractionation ◽  
Isolated Rat Hepatocytes ◽  
Phosphatidate Phosphohydrolase ◽  
Isolated Rat

The incubation of hepatocytes with 1-4mM-oleate increased the total activity of phosphatidate phosphohydrolase that was measured in the presence of Mg2+ to about 2-fold. This was accompanied by an increase in the proportion of the enzyme that was isolated with the particulate fractions. Conversely, the addition of up to 4mM-oleate decreased the recovery of phosphatidate phosphohydrolase in the cytosolic fraction from about 70% to 3% when hepatocytes were lysed with digitonin. Most of the increase in the membrane-associated phosphohydrolase activity was isolated after cell fractionation in the microsomal fraction that was enriched with the endoplasmic-reticulum marker arylesterase. It is proposed that the translocation of phosphatidate phosphohydrolase facilitates the increased synthesis of triacylglycerols in the liver when it is presented with an increased supply of fatty acids.

scholarly journals Calcium rather than cyclic AMP is an intracellular messenger of parathyroid hormone action on glycogen metabolism in isolated rat hepatocytes

1989 ◽  
Vol 258 (3) ◽  
pp. 889-894 ◽  
Author(s):  
T Mine ◽  
I Kojima ◽  
E Ogata
Keyword(s):  
Parathyroid Hormone ◽  
Cyclic Amp ◽  
Glucose Production ◽  
Rat Hepatocytes ◽  
Free Calcium ◽  
Dependent Manner ◽  
Isolated Rat Hepatocytes ◽  
Glucose Output ◽  
Dose Dependent ◽  
Isolated Rat

The synthetic 1-34 fragment of human parathyroid hormone (1-34hPTH) stimulated glucose production in isolated rat hepatocytes. The effect of 1-34hPTH was dose-dependent and 10(10) M-1-34 hPTH elicited the maximum glucose output, which was approx. 80% of that by glucagon. Although 1-34hPTH induced a small increase in cyclic AMP production at concentrations higher than 10(-9) M, 10(-10) M-1-34hPTH induced the maximum glucose output without significant elevation of cyclic AMP. This is in contrast to the action of forskolin, which increased glucose output to the same extent as 10(-10) M-1-34hPTH by causing a 2-fold elevation of cyclic AMP. In addition to increasing cyclic AMP, 1-34hPTH caused an increase in cytoplasmic free calcium concentration ([Ca2+]c). When the effect of 1-34hPTH on [Ca2+]c was studied in aequorin-loaded cells, low concentrations of 1-34hPTH increased [Ca2+]c: the 1-34hPTH effect on [Ca2+]c was detected at as low as 10(-12) M and increased in a dose-dependent manner. 1-34hPTH increased [Ca2+]c even in the presence of 1 microM extracellular calcium, suggesting that PTH mobilizes calcium from an intracellular pool. In line with these observations, 1-34hPTH increased the production of inositol trisphosphate. These results suggest that: (1) PTH activates both cyclic AMP and calcium messenger systems and (2) PTH stimulates glycogenolysis mainly via the calcium messenger system.

Effect of Somatomedin A and Insulin on Cyclic AMP Generation in Isolated Rat Hepatocytes

1980 ◽  
Vol 12 (06) ◽  
pp. 251-256 ◽  
Author(s):  
Rosa Zederman ◽  
Carin Grebing ◽  
Kerstin Hall ◽  
H. Löw
Keyword(s):  
Cyclic Amp ◽  
Rat Hepatocytes ◽  
Isolated Rat Hepatocytes ◽  
Isolated Rat
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