Effect of adenosine on gluconeogenesis in the perfused liver of chicken and guinea-pig

• 1.1. Glucose formation from lactate by the perfused liver of 48 hr starved chickens was strongly inhibited by adenosine (Ado); the half-maximal inhibition was attained at 40 μM. This effect was paralleled by a four- to five-fold increase of ATP content as determined in freeze-clamped liver.
• 2.2. In chicken liver homogenate gluconeogenesis from precursors such as alanine, glutamate, glutamine and aspartate, which are not converted into glucose by the perfused chicken liver, proceeded at rates equal to or higher than that with lactate, being markedly inhibited by Ado.
• 3.3. In the perfused guinea-pig liver glucose synthesis with lactate, propionate, glycerol and fructose was also inhibited by Ado; however, when precursors such as pyruvate, glutamine and a mixture of lactate + pyruvate were supplied to the liver Ado did not inhibit gluconeogenesis.
• 4.4. Assay of adenine nucleotides in the perfused guinea-pig liver, stopped by freeze-clamping technique in a number of experimental variants, revealed no correlation between the rate of gluconeogenesis and the changes induced by Ado in the adenine nucleotide pool.
• 5.5. In the perfused liver of both chicken and guinea-pig Ado produced an increase of the lactate to pyruvate ratio and, in general, a diminution of the content of malate-aspartate shuttle intermediates.
• 6.6. The results are interpreted as suggesting that the inhibitory effect of Ado on hepatic gluconeogenesis is not necessarily mediated by the changes in the adenine nucleotide pool.

     

12-O-tetradecanoylphorbol-13-acetate enhances glycolysis in rat thymocytes

• 1.1. The potent tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) induced a rapid increase in glycolysis in rat thymocytes.
• 2.2. The increase in the glycolytic flux was also reflected by elevated fructose 1,6-diphosphate levels.
• 3.3. TPA treatment did not result in an increase of hexokinase, phosphofructokinase or pyruvate kinase when measured in cell homogenates.
• 4.4. It is suggested that the early increase in glycolysis in TPA treated lymphocytes may result from TPA-mediated increase in glucose transport.

     

Light-induced effects of several enzymes of carbohydrate metabolism in Phycomyces blakesleeanus

• 1.1. The photoregulation shown by glyceraldehyde 3-phosphate dehydrogenase and glucose 6-phosphate dehydrogenase appears to be independent of the mad gene product(s) and also independent of carotene biosynthesis regulation.
• 2.2. The photoregulation of malate dehydrogenase appeared to be dependent on the mutation of the mad and car S genes.
• 3.3. Pyruvate kinase and lactate dehydrogenase may be classified as light-independent.
• 4.4. The action of ATP and fructose 1,6-bisphosphate on the enzymes studied was generally independent of light/dark grown conditions.
• 5.5. However, the effect of fructose 1,6-bisphosphate on Phycomyces pyruvate kinase appears to be light-dependent.

     

Fetal lung metabolism: Response to maternal fasting

• 1.1. Fetal lung metabolic response to maternal fasting late in gestation was investigated.
• 2.2. Maternal fasting 4 days before term was associated with low fetal plasma glucose and insulin levels but increased levels of fetal plasma glucagon, glycerol, lactate and fatty acids.
• 3.3. Fetuses from fasted mothers showed a significant decrease in body weight (30%), lung weight (30%) and lung glycogen (46%), but no change in lung protein, phospholipid or total lung DNA, suggesting that lung size is affected more than maturation.
• 4.4. Fetal lung slices incubated in vitro showed that lactate oxidation to CO₂ equalled that of glucose in control fetal lungs and was unaffected by maternal fasting, while glucose oxidation was depressed (23%).
• 5.5. Maternal fasting significantly decreased in vitro incorporation of [U-¹⁴C]-glucose, [U-¹⁴C]lactate and [1-¹⁴C]palmitate into lung phospholipids.
• 6.6. Fetal lungs from fasted mothers showed increased conversion of lactate to glucose, indicating gluconeogenic potential by fetal lung.
• 7.7. These studies show that plasma lactate serves as an important energy fuel and substrate for lipid synthesis for the fetal lung, and maternal fasting markedly alters fetal lung metabolism.

     

Effects of the nonsteroidal anti-inflammatory drug piroxicam on energy metabolism in the perfused rat liver

• 1.1. The actions of piroxicam, a nonsteroidal and noncarboxylic anti-inflammatory drug, on the metabolism of the isolated perfused rat liver were investigated. The main purpose was to verify if piroxicam is also active on glycogenolysis and energy metabolism, as demonstrated for several carboxylic nonsteroidal anti-inflammatories.
• 2.2. Piroxicam increased oxygen consumption in livers from both fed and fasted rats.
• 3.3. Piroxicam increased glucose release and glycolysis from endogenous glycogen (glycogenolysis).
• 4.4. Gluconeogenesis from lactate plus pyruvate was inhibited.
• 5.5. The action of piroxicam on oxygen consumption was blocked by antimycin A, but not by atractyloside.
• 6.6. The action of piroxicam in the perfused rat liver metabolism seems to be a consequence of its action on mitochondria.
• 7.7. It can be concluded that inhibition of energy metabolism and stimulation of glycogenolysis are not specific properties of carboxylic nonsteroidal anti-inflammatory drugs.

     

The regulation of pyruvate kinase in the hepatopancreas of Carcinus maenas)

• 1.1. Estimation of the activity of pyruvate kinase and pyruvate carboxylase in the hepatopancreas of Carcinus maenas gave values of 28.5 and 7.4 units/g wet wt tissue respectively.
• 2.2. The concentrations of substrates, products and allosteric effectors of these enzymes in hepatopancreas were measured.
• 3.3. The activities of pyruvate kinase and pyruvate carboxylase were redetermined using the approximate physiological range of substrate and effectors.
• 4.4. Under these conditions the effective activity of pyruvate kinase could be decreased to less than 2 units/g wet wt tissue whereas that for the pyruvate carboxylase was 2.6 units/g wet wt tissue indicating that a net synthesis of phosphoenolpyruvate could occur in vivo.

     

Reduction of ferrihemoglobin in erythrocytes of birds and mammals

• 1.1. Species differences exist in ferrihemoglobin reduction rates in bird and mammalian red cells, bird erythrocytes being very active reducers.
• 2.2. Glucose and lactate enhance ferrihemoglobin reduction. In horse and quail red cells β-hydroxybutyrate has this effect as well.
• 3.3. Malate and pyruvate do not enhance ferrihemoglobin reduction.
• 4.4. Plasma addition to red cell suspensions enhances ferrihemoglobin reduction; addition of lactate mimics this effect in all species except the dog.
• 5.5. Incubation conditions are very important for measuring ferrihemoglobin reduction. Especially the presence of bicarbonate ions is essential. In our experiments no inhibition of reduction rates by chloride ions is found.
• 6.6. Mitochondrial NADH production does not play a role in ferrihemoglobin reduction in bird red cells.

     

The effect of time on physiological changes in eel Anguilla anguilla,induced by lindane

• 1.1. Eel were exposed to a sublethal concentration of lindane (0.335 ppm) for 6, 12, 24, 48, 72 and 96 hr.
• 2.2. Concentrations of glycogen, glucose, lactate, pyruvate and lipids were determined in gill tissue after lindane exposure.
• 3.3. Gill glycogen descreased and glucose levels increased at 6 hr of treatment, lactate and pyruvate concentration increased between 6 and 48 hr. Total lipid values decreased between 6 and 24 hr; thereafter, the levels increased up to 72 hr of exposure.
• 4.4. Clear changes were found in all parameters tested in gill tissues. The observed effects of lindane on metabolism in fish are discussed in relation to acute stress syndrome.

     

Cooperative atp inhibition and fructose-1,6-biphosphate activation of rat liver pyruvate kinase

• 1.1. For the determination of relationship between FDP and ATP in the rat liver pyruvate kinase regulation, kinelic studies have been carried out at several ATP and FDP concentrations.
• 2.2. The results obtained on FDP activation show a great cooperativity for FDP saturation with a Hill coefficient of h = 2.79.
• 3.3. Kinetic studies on ATP inhibition also show a great cooperativity for ATP saturation (h = 2.84) at high FDP concentrations.
• 4.4. These results may contribute to explain the regulation of rat liver pyruvate kinase accounting for the activity of this enzyme at high FDP concentrations modulated by small changes in ATP concentrations.

     

In vitro-studies on the anaerobic formation of ethanol by the larvae of Chironomus thummi thummi (Diptera)

• 1.1. The anaerobic formation of ethanol by the larvae of Chironomus thummi thummi was investigated in homogenates and isolated mitochondria.
• 2.2. It was found that homogenates transform fructose-1,6-bisphosphate into ethanol and acetate. The accumulation of ethanol decreases substantially and the formation of acetate almost ceases when arsenite, an inhibitor of pyruvate dehydrogenase, is present in the incubation medium.
• 3.3. The cytosolic fraction of the homogenate was shown to degrade fructose-1,6-bisphosphate to pyruvate only. No ethanol could be detected, although there is high activity of alcohol dehydrogenase in the cytosol.
• 4.4. Isolated mitochondria produce large quantities of ethanol from pyruvate during anoxia. This ethanol production was shown to depend on the presence of NADH. It is deduced that this cosubstrate originates from intramitochondrial formation of acetate from pyruvate, which was always found to accumulate alongside ethanol.

     

Nitrogen metabolism and excretion in the freshwater crayfish Cherax destructor

• 1.1. The pathway leading to the excretion of ammonia in the crustacean, Cherax destructor, has been investigated.
• 2.2. Injection of ammonium chloride and of serine into the haemolymph always led to a rapid increase in the excretion of ammonia. This was not the case with other amino acids. Isolated gills incubated with serine and threonine but not glutamate and glutamine produced ammonia.
• 3.3. Serine dehydratase was present in the gills, midgut gland and tail muscle and serine (0.1 mM) was present in the haemolymph.
• 4.4. The hypothesis is put forward that serine may be the ultimate source of ammonia and that this deaminating reaction is not restricted to the gill. Such a hypothesis sees the formation and deamination of serine—from 3-phosphoglycerate to pyruvate (lactate) as a modified glycolytic pathway.

     

Shift in vivo in the lactate dehydrogenase isoenzyme pattern in experimental models conditioning the metabolic adaptation of rat brain

• 1.1. In order to analyse the possible shift in the lactate dehydrogenase isoenzyme pattern, experimental models affecting the glycolytic pathway are developed, including phenylalanine, thiamine and epinephrine administration, and a vitamin free diet.
• 2.2. The results obtained show that a shift in the lactate dehydrogenase isoenzyme pattern occurs in every change in physiological condition.
• 3.3. These shifts are in accordance with the kinetic properties of each isoenzyme and account for a metabolic adaptation to each physiological state.

     

The effects of oxalate and glucose on lipogenesis by isolated hepatocytes from normal and biotin-deficient chicks (Gallus domesticus)

• 1.1. Isolated hepatocytes synthesize fatty acids and cholesterol from lactate and acetate with lactate being the more effective substrate.
• 2.2. Biotin deficiency decreased fatty add synthesis from both substrates but stimulated cholesterogenesis.
• 3.3. Exposure of intact hepatocytes to oxalate inhibited fatty acid and cholesterol synthesis from lactate, this effect was enhanced in biotin-deficient chicks. A similar effect was not observed when acetate was the substrate.
• 4.4. Synthesis of fatty acids from lactate and acetate was stimulated by glucose, biotin deficiency increased this response. Cholesterogenesis was reduced in control but not biotin-deficient chicks.

     

End products of carbohydrate metabolism in Trichomonas vaginalis

• 1.1. The major excreted acidic end products of the anaerobic and aerobic carbohydrate metabolism of Trichomonas vaginalis (ATCC 30001) were acetate and lactate. Glycerol-1-phosphate, pyruvate, malate and ethanol were also detected in the incubation medium, but they represented less than 3% of the total carbon excreted. Succinate could not be found. Under anaerobic conditions H₂ and CO₂ were produced. Under aerobic conditions O₂ was consumed and CO₂ produced.
• 2.2. In the absence of exogeneous carbohydrate more acetate than lactate was produced. Glucose (50 mM) significantly increased acid production with lactate becoming the predominant product. Glucose also increased the anaerobic and aerobic gas exchange.
• 3.3. In the presence of 5% CO₂ there were no significant changes in carbohydrate utilization and acid production.
• 4.4. Aerobiosis was accompanied by increased carbohydrate utilization and end product formation. No Pasteur effect could be observed.

     

Serum lipids,thyroxine and catecholamine levels in the reindeer with reference to the annual climatic cycle

• 1.1. Blood glucose and lactate, serum total lipid and triglyceride, thyroxine (T₄), epinephrine and norepinephrine concentrations and serum dopamine-β-hydroxylase activity were studied in 76 reindeer hinds and 127 calves with reference to the seasons.
• 2.2. Blood glucose level tended to be lowest in Autumn, and blood lactate highest in Summer.
• 3.3. Serum total lipids were smallest in Spring (2.8 g/l) and greatest in Autumn (5.3 g/l). Triglycerides were smallest in Winter (0.18 mmol/l) and highest in Autumn (0.32 mmol/l). In calves the total lipids increased during the neonatal period.
• 4.4. Serum epinephrine correlated with the weight, age, blood glucose and total lipids of the animals. In adult animals the lowest serum epinephrine level was found in Spring and the highest in Autumn (55 vs 190 ng/ml).
• 5.5. Serum norepinephrine concentration and dopamine-β-hydroxylase activity were highest in Spring and decreased towards Autumn. Parturition affected these parameters significantly.
• 6.6. The preponderance of high levels of some blood constituents in Autumn may be attributable to the replenishment of energy supplies for Winter time and also to the rutting season.
• 7.7. T₄ was smallest in Spring and highest in Summer. It was slightly greater in Winter than in Autumn. This suggests that the metabolic rate is tower in Winter than in Summer. Thus, the adaptation of the reindeer to a cold climate mainly utilizes insulation.

     

Enzymes of fructose metabolism in the intestinal mucosa of the rat (Rattus norvegicus). Localization along the small intestine; consequences of dietary fructose

• 1.1. The activities of all the eight enzymes of conversion of fructose to glucose, of all the three key enzymes of glycolysis and of the two dehydrogenases of pentose shunt were determined in proximal and distal mucosa of small intestine.
• 2.2. With the exception of hexokinase, all of these enzymes have an activity significantly higher in the proximal than distal mucosa.
• 3.3. The gradient along the intestine is particularly important for the three enzymes which are typical for fructose metabolism (ketohexokinase, triokinase and fructose-1-phosphate aldolase), for glucose-6-phosphatase and for phosphofructokinase.
• 4.4. The effects of fructose diet on the enzyme activities are compatible with the results, described in other papers, concerning the final products of metabolism.
• 5.5. The increase of fructose metabolism appears to result mainly from the stimulation of the activities of ketohexokinase and fructose-1-phosphate aldolase which control all the pathways of ketohexose utilization.
• 6.6. The activation of glucose-6-phosphatase, in comparison with the other enzymes which are involved in glucose-6-phosphate metabolism, explains the appearance of the ability to synthesize glucose with fructose as substrate. This enzyme is the only key enzyme of fructose to glucose conversion which responds to fructose feeding in distal mucosa.
• 7.7. The activities of hexokinase and phosphofructokinase are not increased by fructose feeding.
• 8.8. The activity of pyruvate kinase. the only key glycolytic enzyme which is necessarily implicated when fructose is the substrate, is stimulated but less than the typical enzymes of fructose metabolism.
• 9.9. But, because of its quantitative importance, the glycolytic pathway is responsible for the most part of the observed increase of fructose utilization.
• 10.10. The responses of pyruvate kinase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities to fructose feeding are similar in the two parts of small intestine.
• 11.11. The activities of ketohexokinase, triokinase and glucose-6-phosphate isomerase are stimulated only in the proximal small intestine mucosa.
• 12.12. The other enzyme activities which are stimulated in proximal segment are also increased in distal segment.
• 13.13. All segments of small bowel show adaptive changes to dietary manipulation but not necessarily for all their functions.
• 14.14. The gradient of enzyme activities from the proximal to the distal small intestine persists despite dietary modification, but the data do not determine that this gradient is intrinsic or that it is not intrinsic.

     

In vitro substrate utilization for lipid synthesis in liver explants from hyperthyroid chickens

• 1.1. Indian River male broiler chickens growing from 7 to 28 days of age were fed diets containing 12, 18, 24 and 30% protein + 0 or 1 mg triiodothyronine (T₃)/kg of diet to study energetic costs of lipogenesis and the use of various substrates for in vitro lipogenesis.
• 2.2. De novo lipid and CO₂ production were determined in the presence of [1-¹⁴C]pyruvate, [2-¹⁴q]pyruvate, [3-¹⁴C]pyruvate, [2-¹⁴C]acetate and [U-¹⁴C]alanine.
• 3.3. Oxygen consumption was determined in mitochondrial preparations to estimate the energetic costs in expiants synthesizing lipid.
• 4.4. Radiolabeled CO₂ derived from [1-¹⁴C]pyruvate was used as an estimate of coenzyme A availability in liver expiants. Lipids derived from [2-¹⁴C]pyruvate, [2-¹⁴C]acetate and [U-¹⁴C]alanine estimate relative substrate efficiency.
• 5.5. Labeled CO₂ production from [1-¹⁴C]pyruvate was greatest in that group fed a 12% protein diet and least in the group fed a 30% protein diet.
• 6.6. In addition, T₃ increased CO₂ production from [1-¹⁴C]pyruvate.
• 7.7. The production of ¹⁴CO₂ from the second carbon of pyruvate or acetate was increased by T₃.
• 8.8. The low-protein diet (12% protein) increased (P <0.05) lipogenesis.
• 9.9. Adding T₃ to the diets decreased carbon flux into lipid from all substrates, but increased CO₂ production from all substrates without changing stage 3 and 4 respiration rates in mitochondrial preparations.
• 10.10. These observations imply that coenzyme A availability may have regulated de novo lipogenesis in the present study.
• 11.11. It was also concluded that previously noted effects of T₃ on intermediary metabolism may involve metabolic pathways that do not involve changes in mitochondrial function.

     

Regulation in vitro of rat liver pyruvate kinase by phosphorylation-dephosphorylation reactions,catalyzed by cyclic-AMP dependent protein kinases and a histone phosphatase

• 1.1.Cyclic-AMP dependent protein kinases, resolved by chromatography on DEAE-cellulose and hydroxylapatite, catalysed the phosphorylation of rat liver pyruvate kinase and calf thymus histones by [γ^{3 2}P]ATP. [^{3 2} P]phosphopeptides, from acid hydrolysates of pyruvate kinase phosphorylated by the different protein kinase fractions, displayed identical electrophoretic patterns. Phosphorylation inhibited pyruvate kinase activity.
• 2.2.Full activity was restored when phosphorylated pyruvate kinase was dephosphorylated by a histone phosphatase from the soluble fraction of rat liver. These results are consistent with the hypothesis that pyruvate kinase is regulated by phosphorylation-dephosphorylation reactions.

     

Novel amino acid linked dehydrogenase in the sponge Halichondria panicea (pallas)

• 1.1. The sponge Halichondria panicea has a complete sequence of glycolytic and tricarboxylic acid cycle enzymes.
• 2.2. However, there is no detectable lactate dehydrogenase in H. panicea and lactate dehydrogenase appears to be functionally replaced by an enzyme which catalyses the reductive condensation of pyruvate and glycine to yield 2-methylimino-diacetic acid (strombine).
• 3.3. The intracellular distribution and kinetic properties of this novel enzyme (strombine dehydrogenase) have been investigated and its role in metabolism is discussed.

     

The erythrocytes of the metallic skink Niveoscineus metallicus

• 1.1. We studied the haemoglobin content, erythrocyte indices, erythrocyte enzymes and haemoglobin electrophoresis patterns of the metallic skink Niveoscineus metallicus and compared them to the small amount of published data on other small lizards.
• 2.2. Haemoglobin was much lower than that recorded for the salamander.
• 3.3. Erythrocyte enzymes (glucose phosphate isomerase and glucose 6 phosphate dehydrogenase) were lower in the skink than in the salamander. Glyceraldehyde phosphate dehydrogenase, phosphoglycerate kinase and pyruvate kinase were much higher in the skink than in the salamander.
• 4.4. A single, slow, haemoglobin component was identified by electrophoresis.