Regulation of Fat Metabolism in the Liver

Mayes, Peter A.; Felts, James M.

doi:10.1038/215716a0

Cited by 189 publications

(81 citation statements)

References 14 publications

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“…This as well as the collection and measurement of 14C0, has been described previously [4]. Isolation and counting of 14C-labelled ketone bodies was carried out according to Mayes and Felts [20].…”

Section: Isotope Experimentsmentioning

confidence: 99%

Regulation of Gluconeogenesis in the Guinea Pig Liver

Söling

Wilims

Kleineke

et al. 1970

European Journal of Biochemistry

154

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Because of differences in the pattern of enzyme activities involved in glycolysis and gluconeogenesis between rat and guinea pig liver, the regulation of gluconeogenesis in guinea pig liver was studied.The following results were obtained: 1. Starvation increases the capacity for gluconeogenesis from pyruvate in vivo. 2. Ghconeogenesis from L-lactate and from pyruvate in isolated perfused livers is greater in the guinea pig than in the rat, whereas gluconeogenesis from other precursors is similar in both species.3. Long chain and medium chain fatty acids inhibit gluconeogenesis from L-lactate in isolated perfused guinea pig liver but stimulate gluconeogenesis from L-lactate in isolated perfused rat liver. I n the guinea pig liver the difference does not result from a lower rate of fatty acid oxidation but from a greater reduction in the cytoplasmic NAD+/NADH system.During enhanced fatty acid oxidation in guinea pig liver and in rat liver, similar changes in the concentrations of both acetyl-S-CoA and CoA-XH are observed.With high concentrations of pyruvate as the gluconeogenic precursor, both fatty acids and ethanol lead to a slight stimulation of glucose formation by supplying hydrogen equivalents to the cytosolic NAD+/NADH system. 4. Both glucagon and dibutyryl-Ado-3' ; 5'-P stimulate ureogenesis and ketogenesis in isolated perfused guinea pig liver. However, the stimulation of gluconeogenesis by glucagon and Ado-3';5'-P normally observed in isolated perfused rat livers was not found in isolated perfused guinea pig livers.5. Partially purified pyruvate carboxylases from rat and guinea pig liver do not differ with respect to the apparent K , values for pyruvate and ATP, and also the apparent K , values for acetyl-S-CoA a t different pH values. At constant concentrations of MgATP2-or MnATP2-the pH-optima for the guinea pig enzyme are significantly lower.6. 5-Methoxyindole-2-carbonic acid inhibits gluconeogenesis in guinea pig liver in the same way as in rat liver. Quinolinate, on the other hand is far less inhibitory in guinea pig liver and does not inhibit a t all in isolated perfused pigeon livers.7. Major species differences are found when the activities of the rate limiting enzymes involved in gluconeogenesis are measured under V,,, conditions. Pyruvate carboxylase activity is in the same range in rat and guinea pig liver; pyruvate kinase activity is considerably lower, phosphoenolpyruvate carboxykinase activity is considerably higher in guinea pig liver. According to our results gluconeogenesis in guinea pig liver from lactate or pyruvate is mainly regulated by the concentration of pyruvate.The difference in the regulation of gluconeogenesis between rat and guinea pig liver probably results from a difference in the compartmentalization of phosphoenolpyruvate carboxykinase. A higher rate of futile cycling between phosphoenolpyruvate and pyruvate in rat liver, due to the higher activity of pyruvate kinase in relation to the activities of phosphoenolpyruvate carboxykinase and pyruvate carboxylase, may also cont...

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Section: Isotope Experimentsmentioning

confidence: 99%

Regulation of Gluconeogenesis in the Guinea Pig Liver

Söling

Wilims

Kleineke

et al. 1970

European Journal of Biochemistry

154

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“…It has been well demonstrated that the alteration in the rate of fatty acid oxidation either in mitochondrial (10) or peroxisomal pathway (11) in the liver modify the availability of fatty acids for triacylglycerol synthesis and alter the very low density lipoprotein production by the liver. Moreover, there are evidences to support the concept that the rates of fatty acid oxidation and synthesis in the liver are inversely proportional to each other under various nutritional and pathological conditions (12)(13)(14)(15)(16)(17)(18). Thus, there is a possibility that the ingestion of phospholipid alters not only the rate of the fatty acid synthesis but also the rate of the fatty acid oxidation and these changes contribute to the hypolipidemic effect of soybean phospholipid.…”

mentioning

confidence: 99%

Effect of Dietary Soybean Phospholipid and Fats Differing in the Degree of Unsaturation on Fatty Acid Synthesis and Oxidation in Rat Liver.

Kabir

Ishii²

1995

Journal of Nutritional Science and Vitaminology, J Nutr Sci Vit

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SummaryThe activities of enzymes in fatty acid oxidation and synthesis in the liver of rats fed soybean phospholipids and soybean oil corresponding to the dietary levels of 3% fatty acid added to the diets containing a saturated fat (coconut oil) and a polyunsaturated fat (salflower oil) at the amounts corresponding to 12% fatty acid levels were compared. Soybean phospholipid compared with soybean oil added to both coconut and safflower oil diets significantly reduced the activities of enzymes in fatty acid synthesis (fatty acid synthetase, glucose-6-phosphate dehydrogenase and malic enzyme).However, there were no significant differences in the activities of enzymes in fatty acid oxidation (carnitine palmitoyltransferase, acyl-CoA dehydrogenase and acyl-CoA oxidase) between the groups of rats fed soybean phospholipid and soybean oil added to coconut and safflower oil diets except for one occasion. Soybean phospholipid compared with soybean oil added to coconut oil diet significantly decreased the concentrations of triacylglycerol, choresterol and phospholipid in the serum and of triacylglycerol and cholesterol in the liver. However, the dietary phospholipid added to safflower oil diet failed to alter these values. These results suggested that the alteration in the rate of fatty acid synthesis, but not oxidation, in the liver is responsible for the lipid-lowering effect of dietary soybean phospholipid added to a saturated fat diet. Key Words soybean phospholipid, fatty acid synthesis, fatty acid oxidation, rat liver Dietary phospholipids from various origins exert a potent lipid-lowering effect not only in experimental animals (1-3) but also in humans (4, 5). Regarding the mechanism by which phospholipids reduce serum lipid concentrations, we have previously demonstrated that the diets containing soybean phospholipid and egg * Present address:

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“…It is expected that a large proportion of the fatty acids that enter the liver in these conditions will be oxidized. The preference for fatty acid oxidation versus esterification to triacylglycerol is especially well observed in starvation (Mayes & Felts, 1967;Imazumi et al, 1973;Mayes, 1976;Iritani et al, 1976;Groener & van Golde, 1977). A decreased rate of triacylglycerol synthesis has been reported with cell-free preparations obtained from the livers of starved rats (Rubenstein & Rubenstein, 1966;Fallon & Kemp, 1968).…”

Section: Resultsmentioning

confidence: 93%

The effect of chronic diabetes, induced by streptozotocin, on the activities of some enzymes of glycerolipid synthesis in rat liver

1978

Biochemical Journal

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1. Rats were injected with a single dose of 35mg of streptozotocin/kg body wt. They exhibited a diabetes that was characterized by glycosuria, polyuria, polydipsia, hyperphagia, hyperglycaemia, increased concentrations of unesterified fatty acids, glycerol and triacylglycerols in the serum and an increased activity of glucose 6-phosphatase in the liver. 2. After 10 weeks the hepatic activities of the microsomal glycerol phosphate acyltransferase, phosphatidate phosphohydrolase, phosphatidate cytidylyltransferase, diacylglycerol acyltransferase, choline phosphotransferase, CDP-diacylglycerol-inositol phosphatidyltransferase and the soluble phosphatidate phosphohydrolase were measured. 3. The only significant changes were an increase in the activity of the soluble phosphatidate phosphohydrolase and a decrease in that of the CDP-diacylglycerolinositol phosphatidyltransferase in the diabetic rats. 4. These results are discussed in relation to the control of glycerolipid synthesis.Diabetes mellitus is characterized by hyperglycaemia, which is often accompanied by glycosuria, and by an increase in the consumption of food and water and in urine output. In severe cases there is ketonaemia, ketonuria and hypertriglyceridaemia. The last is usually caused by an accelerated secretion of very-low-density lipoprotein, and the severity of the hypertriglyceridaemia can be taken as an indication of the adequacy of the control of the diabetes (Nikkila & Kekki, 1973;Nikkila, 1974).In the present study rats were made chronically diabetic by a single injection of streptozotocin. These animals were then used to investigate whether the diabetic state is accompanied by changes in the relative activities of the enzymes responsible for the synthesis ofglycerolipids in the liver. It is hoped that these results will add to our understanding of how glycerolipid synthesis is controlled.

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Regulation of Fat Metabolism in the Liver

Cited by 189 publications

References 14 publications

Regulation of Gluconeogenesis in the Guinea Pig Liver

Regulation of Gluconeogenesis in the Guinea Pig Liver

Effect of Dietary Soybean Phospholipid and Fats Differing in the Degree of Unsaturation on Fatty Acid Synthesis and Oxidation in Rat Liver.

The effect of chronic diabetes, induced by streptozotocin, on the activities of some enzymes of glycerolipid synthesis in rat liver

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