scholarly journals Fatty acids reverse the cyclic AMP inhibition of triacylglycerol and phosphatidylcholine synthesis in rat hepatocytes

1983 ◽  
Vol 216 (1) ◽  
pp. 129-136 ◽  
Author(s):  
S L Pelech ◽  
P H Pritchard ◽  
D N Brindley ◽  
D E Vance
Keyword(s):  
Fatty Acids ◽  
Cyclic Amp ◽  
Rat Hepatocytes ◽  
Phosphocholine Cytidylyltransferase ◽  
Triacylglycerol Synthesis ◽  
Monolayer Cultures ◽  
Membrane Bound ◽  
Amp Inhibition ◽  
Phosphatidylcholine Synthesis

The influence of cyclic AMP analogues and fatty acids on glycerolipid biosynthesis in monolayer cultures of rat hepatocytes was investigated. Chlorophenylthio-cyclic AMP and adenosine 3′:5′-cyclic phosphorothioate inhibited the rate of triacylglycerol synthesis from [1(3)-3H]glycerol, and phosphatidylcholine synthesis from [Me-3H]-choline. Supplementation of the hepatocytes with palmitate (1 mM) reversed chlorophenylthio-cyclic AMP inhibition of triacylglycerol synthesis. Similarly, cyclic AMP analogue-inhibition of phosphatidylcholine synthesis was abolished when the cells were simultaneously incubated with oleate (3 mM). Reactivation of phosphatidylcholine synthesis in chlorophenylthio-cyclic AMP-supplemented cells with oleate was accompanied by conversion of CTP: phosphocholine cytidylyltransferase into the membrane-bound form, since these cells released the enzyme more slowly after treatment with digitonin. The opposing actions of cyclic AMP and fatty acids are discussed in relation to the regulation of glycerolipid biosynthesis during starvation, diabetes and stress.

scholarly journals Triacylglycerol synthesis in goat mammary gland. Factors influencing the esterification of fatty acids synthesized de novo

1984 ◽  
Vol 220 (2) ◽  
pp. 521-527 ◽  
Author(s):  
H O Hansen ◽  
I Grunnet ◽  
J Knudsen
Keyword(s):  
Fatty Acids ◽  
Mammary Gland ◽  
Fatty Acid ◽  
De Novo ◽  
Acid Synthesis ◽  
Diacylglycerol Acyltransferase ◽  
Exogenous Fatty Acid ◽  
Triacylglycerol Synthesis ◽  
Membrane Bound

ATP alone had no effect on incorporation of fatty acids synthesized de novo and membrane-bound diacylglycerol into triacylglycerol. Combined addition of ATP and Mg2+ totally inhibits incorporation of fatty acids synthesized de novo and stimulated incorporation of membrane-bound diacylglycerol. ATP, Mg2+ and glycerol 3-phosphate stimulate incorporation of fatty acids synthesized de novo into triacylglycerol, but inhibited the incorporation of membrane-bound diacylglycerol. Diacylglycerol generated in situ was shown to be superior to diacylglycerols preloaded on the membrane as substrate for the diacylglycerol acyltransferase. A model is proposed to explain the effect of absorbed exogenous fatty acid on fatty acid synthesis de novo in goat mammary gland.

scholarly journals Longer-term regulation of pyruvate dehydrogenase kinase in cultured rat hepatocytes

1989 ◽  
Vol 257 (2) ◽  
pp. 487-491 ◽  
Author(s):  
D R Marchington ◽  
A L Kerbey ◽  
M G Giardina ◽  
A E Jones ◽  
P J Randle
Keyword(s):  
Fatty Acids ◽  
Cyclic Amp ◽  
Pyruvate Dehydrogenase ◽  
Kinase Activity ◽  
Rat Hepatocytes ◽  
Pyruvate Dehydrogenase Kinase ◽  
Activator Protein ◽  
Cultured Rat Hepatocytes ◽  
Culture Of Hepatocytes

The activities of pyruvate dehydrogenase (PDH) kinase and of PDH kinase activator protein (KAP) were increased 2-2.4-fold during 25 h of culture of hepatocytes from fed rats with glucagon plus n-octanoate. PDH kinase activity in hepatocytes from starved rats (initially 2.2 x fed control) fell during 25 h of culture in medium 199 (to 1.5 x fed control), but was maintained by glucagon plus octanoate. Dibutyryl or 8-bromo cyclic AMP increased PDH kinase activity 2-2.2-fold in hepatocytes from fed rats, but phenylephrine and isoproterenol (isoprenaline) were without effect. Insulin blocked the action of glucagon to increase PDH kinase activity and decreased the effect of octanoate and octanoate plus glucagon. It is suggested that the effects of starvation to increase activities of PDH kinase and of KAP in liver are mediated by alterations in circulating concentrations of glucagon, fatty acids and insulin and in hepatic cyclic AMP.

scholarly journals Factors regulating the secretion of lysophosphatidylcholine by rat hepatocytes compared with the synthesis and secretion of phosphatidylcholine and triacylglycerol. Effects of albumin, cycloheximide, verapamil, EGTA and chlorpromazine

1988 ◽  
Vol 253 (3) ◽  
pp. 687-692 ◽  
Author(s):  
A Graham ◽  
A J Bennett ◽  
A A M McLean ◽  
V A Zammit ◽  
D N Brindley
Keyword(s):  
Fatty Acids ◽  
Polyunsaturated Fatty Acids ◽  
Rat Hepatocytes ◽  
Absolute Concentration ◽  
Monolayer Cultures ◽  
The Absolute

1. The synthesis and secretion of glycerolipid by monolayer cultures of rat hepatocytes was measured by determining the incorporations of [3H]glycerol, [3H]oleate and [14C]choline and by the absolute concentration of triacylglycerol. 2. The presence of albumin in the medium stimulated the accumulation of lysophosphatidylcholine in the medium by 11-13-fold. 3. Cycloheximide did not significantly alter the accumulation of lysophosphatidylcholine. 4. This process was particularly sensitive to inhibition by chlorpromazine and verapamil, compared with the secretion of triacylglycerol and phosphatidylcholine. By contrast, it was relatively less sensitive to EGTA. 5. It is suggested that intracellular Ca2+ may be important in the production of lysophosphatidylcholine, which then accumulates in the medium by binding to albumin. In vivo this lysophosphatidycholine may be a means of delivering choline and polyunsaturated fatty acids to other organs.

scholarly journals Responsiveness to glucagon by isolated rat hepatocytes controlled by the redox state of the cytosolic nicotinamide—adenine dinucleotide couple acting on adenosine 3′:5′-cyclic monophosphate phosphodiesterase

1978 ◽  
Vol 176 (3) ◽  
pp. 805-816 ◽  
Author(s):  
M G Clark ◽  
I G Jarrett
Keyword(s):  
Cyclic Amp ◽  
Redox State ◽  
Rat Hepatocytes ◽  
Hormonal Control ◽  
Maximal Velocity ◽  
Isolated Rat Hepatocytes ◽  
Cyclic Amp Phosphodiesterase ◽  
Membrane Bound ◽  
Glucose Output ◽  
Isolated Rat

1. The effects of changes in the cytoplasmic [NADH]/[NAD+] ratio on the efficacy of glucagon to alter rates of metabolism in isolated rat hepatocytes were examined. 2. Under reduced conditions (with 10mM-lactate), 10nM-glucagon stimulated both gluconeogenesis and urea synthesis in isolated hepatocytes from 48h-starved rats; under oxidized conditions (with 10mM-pyruvate), 10nM-glucagon had no effect on either of these rates. 3. The ability of glucagon to alter the concentration of 3′:5′-cyclic AMP and the rates of glucose output, glycogen breakdown and glycolysis in cells from fed rats were each affected by a change in the extracellular [lactate]/[pyruvate] ratio; minimal effects of glucagon occurred at low [lactate]/[pyruvate] ratios. 4. Dose-response curves for glucagon-mediated changes in cyclic AMP concentration and glucose output indicated that under oxidized conditions the ability of glucagon to alter each parameter was decreased without affecting the concentration of hormone at which half-maximal effects occurred. 5. The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (0.05 mM) significantly reversed the inhibitory effects of pyruvate on glucagon-stimulated glucose output. 6. For exogenously added cyclic [3H]AMP(0.1 mM), oxidized conditions decreased the stimulatory effect on glucose output as well as the intracellular concentration of cyclic AMP attained, but did not alter the amount of cyclic [3H]AMP taken up. 7. The effects of lactate, pyruvate, NAD+ and NADH on cyclic AMP phosphodiesterase activities of rat hepatocytes were examined. 8. NADH (0.01–1 MM) inhibited the low-Km enzyme, particularly that which was associated with the plasma membrane. 9. The inhibition of membrane-bound cyclic AMP phosphodiesterase by NADH was specific, reversible and resulted in a decrease in the maximal velocity of the enzyme. 10. It is proposed that regulation of the membrane-bound low-Km cyclic AMP phosphodiesterase by nicotinamide nucleotides provides the molecular basis for the effect of redox state on the hormonal control of hepatocyte metabolism by glucagon.

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.

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