scholarly journals Induction and suppression of the key enzymes of glycolysis and gluconeogenesis in isolated perfused rat liver in response to glucose, fructose and lactate

1973 ◽  
Vol 134 (1) ◽  
pp. 143-156 ◽  
Author(s):  
Janet M. Wimhurst ◽  
K. L. Manchester
Keyword(s):  
Phosphoenolpyruvate Carboxylase ◽  
Pyruvate Carboxylase ◽  
Lactate Concentration ◽  
Sugar Concentration ◽  
Constant Infusion ◽  
Isolated Perfused Rat Liver ◽  
Key Enzymes ◽  
Serine Dehydratase ◽  
High Concentrations ◽  
Blood Sugar Concentration

1. Measurements were made of the activities of the four key enzymes involved in gluconeogenesis, pyruvate carboxylase (EC 6.4.1.1), phosphoenolpyruvate carboxylase (EC 4.1.1.32), fructose 1,6-diphosphatase (EC 3.1.3.11) and glucose 6-phosphatase (EC 3.1.3.9), of serine dehydratase (EC 4.2.1.13) and of the four enzymes unique to glycolysis, glucokinase (EC 2.7.1.2), hexokinase (EC 2.7.1.1), phosphofructokinase (EC 2.7.1.11) and pyruvate kinase (EC 2.7.1.40), in livers from starved rats perfused with glucose, fructose or lactate. Changes in perfusate concentrations of glucose, fructose, lactate, pyruvate, urea and amino acid were monitored for each perfusion. 2. Addition of 15mm-glucose at the start of perfusion decreased the activity of pyruvate carboxylase. Constant infusion of glucose to maintain the concentration also decreased the activities of phosphoenolpyruvate carboxylase, fructose 1,6-diphosphatase and serine dehydratase. Addition of 2.2mm-glucose initially to give a perfusate sugar concentration similar to the blood sugar concentration of starved animals had no effect on the activities of the enzymes compared with zero-time controls. 3. Addition of 15mm-fructose initially decreased glucokinase activity. Constant infusion of fructose decreased activities of glucokinase, phosphofructokinase, pyruvate carboxylase, phosphoenolpyruvate carboxylase, glucose 6-phosphatase and serine dehydratase. 4. Addition of 7mm-lactate initially elevated the activity of pyruvate carboxylase, as also did constant infusion; maintenance of a perfusate lactate concentration of 18mm induced both pyruvate carboxylase and phosphoenolpyruvate carboxylase activities. 5. Addition of cycloheximide had no effect on the activities of the enzymes after 4h of perfusion at either low or high concentrations of glucose or at high lactate concentration. Cycloheximide also prevented the loss or induction of pyruvate carboxylase and phosphoenolpyruvate carboxylase activities with high substrate concentrations. 6. Significant amounts of glycogen were deposited in all perfusions, except for those containing cycloheximide at the lowest glucose concentration. Lipid was found to increase only in the experiments with high fructose concentrations. 7. Perfusion with either fructose or glucose decreased the rates of ureogenesis; addition of cycloheximide increased urea efflux from the liver.

Glucose and lactate kinetics after endotoxin administration in dogs.

1977 ◽  
Vol 232 (2) ◽  
pp. E180 ◽  
Author(s):  
R R Wolfe ◽  
D Elahi ◽  
J J Spitzer
Keyword(s):  
Lactate Concentration ◽  
Constant Infusion ◽  
Glucose Turnover ◽  
Metabolic Clearance ◽  
Plasma Lactate ◽  
Metabolic Clearance Rate ◽  
Metabolic Substrate ◽  
E Coli ◽  
Lactate Kinetics ◽  
Plasma Lactate Concentration

We studied the effects of E. coli endotoxin on the glucose and lactate kinetics in dogs by means of the primed constant infusion of [6(-3)H] glucose and Na-L-(+)-[U-14C] lactate. The infusion of endotoxin induced a transient hyperglycemic level, followed by a steady fall in plasma glucose to hypoglycemic levels. The rate of appearance (Ra) and the rate of disappearance (Rd) of glucose were both significantly elevated (P less than .05) for 150 min after endotoxin, after which neither differed from the preinfusion value. The metabolic clearance rate of glucose was significantly elevated at all times 30 min postendotoxin. By 30 min postendotoxin, Ra and Rd of lactate, plasma lactate concentration, and the percent of glucose turnover originating from lactate were significantly elevated and remained so for the duration of the experiment. We concluded that after endotoxin hypoglycemia developed because of an enhanced peripheral uptake of glucose and a failure of the liver to maintain an increased Ra of glucose. We also concluded that lactate became an important precursor for gluconeogenesis and an important metabolic substrate.

Increased clearance of lactate after short-term training in men

1995 ◽  
Vol 79 (6) ◽  
pp. 1862-1869 ◽  
Author(s):  
S. M. Phillips ◽  
H. J. Green ◽  
M. A. Tarnopolsky ◽  
S. M. Grant
Keyword(s):  
Blood Lactate ◽  
Clearance Rate ◽  
Maximal Oxygen Consumption ◽  
Lactate Concentration ◽  
Blood Lactate Concentration ◽  
Constant Infusion ◽  
Metabolic Clearance ◽  
Metabolic Clearance Rate ◽  
Short Term ◽  
Mitochondrial Potential

A short-term training model previously shown to result in a tighter metabolic control in working muscle in the absence of an increase in mitochondrial potential was used to examine changes in lactate turnover. Lactate flux was studied before and after 10 days of cycle training [2 h/day at 59% maximal oxygen consumption (VO2max)] in untrained men [VO2max = 45.5 +/- 2.4 (SE) ml.kg-1.min-1). A primed constant infusion of L-[1–13C]lactate was used to examine lactate kinetics during a prolonged exercise protocol (90 min at 59% VO2max). Rate of appearance of lactate increased with exercise (P < 0.01), both pretraining (rest = 30.3 +/- 4.9 ml.kg-1.min-1, exercise = 115 +/- 14 ml.kg-1.min-1) and posttraining (rest = 28.4 +/- 4.7 ml.kg-1.min-1, exercise = 112 +/- 13 ml.kg-1.min-1). Despite a lower blood lactate concentration (P < 0.05) during exercise after training, there was no difference in the rate of appearance of lactate. Training increased (P < 0.05) the metabolic clearance rate of lactate during exercise from 36.8 +/- 4.8 to 51.4 +/- 6.8 ml.kg-1.min-1. These findings indicate that at least part of the lower exercising blood lactate observed after training is due to an increase in metabolic clearance rate. In addition, the lower intramuscular lactate levels suggest a decreased recruitment of glycolysis particularly early in exercise.

scholarly journals Assessment of Diabetic Autonomic Nervous Dysfunction with a Novel Percussion Entropy Approach

Complexity ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Hai-Cheng Wei ◽  
Ming-Xia Xiao ◽  
Na Ta ◽  
Hsien-Tsai Wu ◽  
Cheuk-Kwan Sun
Keyword(s):  
Blood Sugar ◽  
Hba1c Level ◽  
Fasting Blood Sugar ◽  
Sugar Concentration ◽  
Multiscale Entropy ◽  
Small Scale ◽  
Early Screening ◽  
Entropy Index ◽  
Additional Information ◽  
Blood Sugar Concentration

This study investigated the validity of a novel parameter, percussion entropy index (PEI), for assessing baroreflex sensitivity. PEI was acquired through comparing the similarity in tendency of change between the amplitudes of successive digital volume pulse (DVP) signals and changes in R-R intervals (RRI) of successive cardiac cycles. Totally 108 upper middle-aged volunteers were divided into three groups: healthy subjects (Group 1, age 41–80, n=41), those with well-controlled type 2 diabetes mellitus (T2DM) (Group 2, age 41–82, n=36, glycated hemoglobin (HbA1c)<6.5%), and patients with poorly controlled T2DM (Group 3, age 44–77, n=31, HbA1c≧6.5%). Percussion entropy index (PEI) was computed from DVP signals acquired through photoplethysmography (PPG) and RRI from electrocardiogram in 1000 successive cardiac cycles for each subject. Autonomic function was also assessed by Poincaré index (SD1/SD2 ratio, SSR), low- to high-frequency power ratio (LFP/HFP, LHR), and small-scale multiscale entropy index (MEISS) for comparison. Demographic, anthropometric, hemodynamic, and serum biochemical parameters of all testing subjects were obtained for investigating the significance of associations with the three parameters. The results showed that MEISS and PEI successfully discriminated among the three groups (p<0.017). However, only PEI showed significant associations with indicators of both acute (i.e., fasting blood sugar concentration, p<0.017) and chronic (i.e., HbA1c level, p<0.001) blood sugar control. Multivariate analysis also showed significant associations of PEI with fasting blood sugar and HbA1c levels in all subjects. The interpreting effect of the two independent variables, HbA1c level and fasting blood sugar concentration, on PEI was 71.4% and 12.3%, respectively. In conclusion, the results demonstrated that additional information on diabetic autonomic dysfunction can be obtained through comparing two simultaneously acquired physiological time series. The significant associations of percussion entropy index with indicators of blood sugar control also highlight its possible role in early screening of the disease.

Organic Cosolutes as Stabilizers of Phosphoenolpyruvate Carboxylase in Storage: an Interpretation of Their Action

1987 ◽  
Vol 14 (2) ◽  
pp. 203 ◽  
Author(s):  
E Selinioti ◽  
D Nikolopoulos ◽  
Y Manetas
Keyword(s):  
Phosphoenolpyruvate Carboxylase ◽  
Cynodon Dactylon ◽  
Dependent Manner ◽  
Native Protein ◽  
Complete Protection ◽  
Concentration Dependent Manner ◽  
Polymeric Form ◽  
C4 Grass ◽  
High Concentrations ◽  
Protein Bovine Serum Albumin

Phosphoenolpyruvate carboxylase (EC 4.1.1.3 1) is rapidly inactivated in dilute extracts from leaves of the C4 grass Cynodon dactylon (L.) Pers. Physiological osmotica (glycerol, betaine, proline, sorbitol and sucrose) and synthetic inert polymers like polyvinylpyrrolidone and polyethylene glycol prevent inactivation in a concentration-dependent manner. In a partially purified preparation (10.5 �mol CO2 min-1 mg-1), lability to inactivation and the minimum levels of cosolvents needed for complete protection become higher as the protein is diluted. Exogenous protein (bovine serum albumin) was much less effective than native protein in stabilising activity. The results could be interpreted on the basis of the exclusion volume theory and the assumption that the catalytic activity is mainly due to a polymeric form which is maintained only at high concentrations of the enzymic protein.

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