The role of citrate derived from glucose in the acetylcholine synthesis in rat brain synaptosomes

• 1.1. Synaptosomes utilizing glucose or glucose plus malate produced citrate with rates of 2.4 and 7.8 nmol/hr/mg of protein, respectively.
• 2.2. (−)Hydroxycitrate increased citrate net synthesis 4 times and inhibited acetylcholine synthesis by 40%.
• 3.3. Oxygen and glucose consumption as well as lactate and CO₂ production were not changed by this inhibitor.
• 4.4. (−)Hydroxycitrate inhibited utilization of exogenous citrate in synaptosomes by 50%.

     

Metabolite concentrations in electrically stimulated lugworms Arenicola marina

• 1.1. The concentrations of lactate, succinate, alanine, aspartate, acetate and propionate in the lugworm Arenicola marina were measured after 1, 2.5 and 12 hr of continuous electrical stimulation under aerobic and anaerobic conditions.
• 2.2. A continuous increase of the concentrations of alanine and acetate, and a decrease of aspartate occurred during the first 2.5 hr of electrical stimulation. A marked rise of succinate and propionate was observed only in experiments lasting longer than 2.5 hr.
• 3.3. No changes were detected in the concentrations of lactate. Under anoxia the metabolites accumulated at significantly higher rates than under aerobic conditions.

     

The effect of d2o on glycolysis by rat hepatocytes

• 1.1. The effect of incorporating D₂O into the incubation medium on glycolysis and gluconeogenesis by hepatocytes from fasted rats was examined.
• 2.2. The substitution by heavy water, D₂O, at concentrations from 10 to 40%, stimulated glucose uptake, lactate production and CO₂ yields from glucose. At 10 mM glucose, 40% D₂O doubled glucose uptake, increased CO₂ production by 40%, and increased lactate production by 350%.
• 3.3. The stimulation of lactate production decreased at higher glucose concentrations, but was still substantial even at 80 mM glucose.
• 4.4. There was no effect on CO₂ production above glucose concentrations of 30 mM.
• 5.5. Ten percent D₂O showed little inhibition of lactate uptake, its oxidation and gluconeogenesis. At 40% D₂O the inhibition ranged from 10 to 20%.
• 6.6. No effect of D₂O on the rate of glucokinase or glucose-6-phosphatase was observed.
• 7.7. The concentration of fructose, 2,6-P was not affected by D₂O

     

Synthesis of reserved polysaccharide from wax esters accumulated as the result of anaerobic energy generation in Euglena gracilis returned from anaerobic to aerobic conditions

• 1.1. Euglena gracilis SM-ZK (a non-photosynthetic mutant), cultured in Koren-Hutner medium, containing glucose, malate and glutamate as the main nutrients, were incubated anaerobiosis for 24 hr, and then returned to aerobic conditions. Wax esters, which were synthesized from paramylon (the reserved polysaccharide) for ATP generation under anaerobiosis (wax ester fermentation) were promptly degraded immediately after the cells were replenished with sufficient O₂. A large part (about 70%) of the decomposed wax esters were converted back to paramylon.
• 2.2. When cells were fed with [1–14C]acetate or [U-¹⁴C]acetate immediately after transfer from anaerobic to aerobic conditions, radioactivity incorporated into paramylon in the cells fed with [U-¹⁴C]acetate was about 1.5-times as high as that with [1-¹⁴C]acetate, proposing that glyoxylate cycle participates in the conversion from wax esters to paramylon.
• 3.3. Paramylon synthesis from [1-¹⁴C]acetate was considerably activated by anaerobic preincubation of cells for several hours.
• 4.4. Isocitrate lyase and malate synthase occurred in cells cultured in Koren-Hutner medium, but the activities were obviously lower than those in cells grown on ethanol. These enzymes were not induced by the anaerobic preincubation.

     

Contribution of aerobic and anaerobic scope to the total metabolic scope of the desert skink,Chalcides ocellatus (Forskal)

• 1.1. Measurements of aerobic scope (resting and active oxygen consumption rates) and anaerobic scope (resting and active production of lactate rates in the whole body homogenates) were carried out on the desert skink, Chalcides ocellatus at temperatures between 10 and 40°C.
• 2.2. The aerobic scope was maximal around the preferred body temperature with a low thermal temperature dependence above the preferred levels.
• 3.3. During initial stages of forced activity, C. ocellatus employed anaerobic metabolism as its major energy source.

     

Interaction of lipogenic substrates in porcine adipose tissue in vitro

• 1.1. Porcine adipose tissue was incubated with radiolabeled glucose, acetate or lactate. Saturation curves indicated that lactate > glucose > acetate in providing two-carbon units for fatty-acid synthesis.
• 2.2. Competition between individual substrates indicated that lactate was the best lipogenic substrate.
• 3.3. Incubation of all three substrates at concentrations observable in serum indicated that at 5.56mM, glucose was the preferred lipogenic substrate in the presence of 0.1 mM acetate and 1.0 mM lactate.
• 4.4. At elevated concentrations (18.52mM glucose, 1.0 mM acetate and 10.0 mM lactate), acetate and lactate were preferred to glucose as lipogenic substrates.

     

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.

     

Changes in plasma glucose and lipid concentrations during treadmill exercise in domestic fowl

• 1.1. Plasma glucose, non-esterified fatty acid, triglyceride, cholesterol and lactate concentrations were measured during 90 min treadmill exercise at a work intensity of 55–60% maximum.
• 2.2. After 90 min exercise plasma glucose fell by 35% whilst the non-esterified fatty acid concentration rose to as much as 3–4 times resting.
• 3.3. Exercise had no significant effect on plasma cholesterol, triglyceride or lactate concentrations.
• 4.4. The findings indicate a progressive increase in fat utilization during prolonged exercise. Possible hormonal mechanisms underlying exercise-induced changes in lipid and carbohydrate metabolism are discussed.

     

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.

     

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.

     

Glycolytic enzymes of fowl and turkey spermatozoa

• 1.1. It was confirmed that, under anaerobic conditions, fowl spermatozoa formed lactate from glucose thirteen times faster than turkey spermatozoa.
• 2.2. The profiles of glycolytic enzyme activities were similar for spermatozoa from both species; however fowl spermatozoal activities were generally 2- to 4-fold higher.
• 3.3. Exceptions were glycerophosphate mutase and lactate dehydrogenase activities which were respectively 9.5 and 41 times greater in fowl spermatozoa.
• 4.4. In both species, spermatozoal glyceraldehyde-3-phosphate dehydrogenase had the lowest activity of the glycolytic enzymes.

     

The effect of temperature on the acid-base status of the blood of the hatching quail (Coturnix c. japonica)

• 1.1. The ambient temperature of embryos of pipped eggs was reduced from 38 to 28°C for a period of 45 min.
• 2.2. The blood P_CO2 was lower and the blood more alkaline at 28°C than at 38°C.
• 3.3. At 28°C plasma [HCO₃⁻] ] was lower than predicted from the blood buffer line determined in vitro.
• 4.4. The plasma concentrations of strong ions and lactate were the same at both temperatures.
• 5.5. After the ambient temperature had been returned to 38°C for a period of 45 min, blood pH was more acidic than before cooling, but there was no difference in blood P_CO2.
• 6.6. The plasma [HCO₃⁻] was the same as that at 28°C and plasma [K⁺] was higher than before cooling.
• 7.7. The results arc discussed in relation to the factors affecting blood pH in embryos at this stage of development.

     

Anaerobic amino acid metabolism in the locust nervous system

• 1.1. Changes in the concentration of amino acids and other metabolites have been followed in the isolated locust nervous system under anaerobic conditions.
• 2.2. The results (accumulation of alanine, pyruvate, lactate, succinate and α-glycerophosphate, decline in asparate, glutamine and glycogen) are qualitatively similar to those found in many other invertebrate and vertebrate tissues, although the pathways in the insect tissue show some differences.
• 3.3. The locust nervous tissue does not show that very large accumulation of α-glycerophosphate shown by whole insects, and which is due to the influence of the flight muscle.
• 4.4. It can be concluded that the locust nervous system has only a limited capacity for anaerobic metabolism, and cannot support normal nervous activity for more than a few minutes in the absence of O₂.

     

Effect of pH on metabolism of the glutamine carbon skeleton by renal cortical mitochondria

• 1.1. To determine the effect of altered acid-base homeostasis on the intramitochondrial metabolism of the glutamine carbon skeleton ¹⁴CO₂ production from [U-¹⁴C]glutamine by isolated rat renal cortical mitochondria was measured.
• 2.2. Mitochondria from rats with chronic metabolic acidosis either showed no change or diminished ¹⁴CO₂ production in comparison with pair fed controls.
• 3.3. By contrast, when the pH of the medium incubating mitochondria from normal rats was manipulated (pH 7.0, 7.4, 7.7), ¹⁴CO₂ production was clearly altered, but the direction and magnitude of the change depended on the glutamine concentration used (0.5 or 10.0 mM).
• 4.4. Mitochondria produced significant quantities of ¹⁴CO₂ when [1,4 ¹⁴C]succinate was used as substrate, indicating that ¹⁴CO₂ production from glutamine does not originate solely from the decarboxylation of α KG.
• 5.5. Thus chronic acidosis and pH, per se, affect intramitochondrial glutamine carbon skeleton metabolism in different fashions, but the specific mechanism cannot be elucidated using ¹⁴CO₂ production from [U-¹⁴C]glutamine.
• 6.6. Additional studies directly quantitating the metabolic products of glutamine have confirmed these findings and more precisely defined the sites of metabolic alteration.

     

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.

     

Facultative aestivation in a tropical freshwater turtle Chelodina rugosa

• 1.1. Chelodina rugosa dug from aestivation sites at the end of the dry season were immediately alert and well coordinated.
• 2.2. Compared with non-aestivating animals, aestivating turtles had 20% higher plasma osmotic pressure and 7% higher sodium. Coupled with a small, but significant weight gain upon return to the water, this suggested the occurrence of minor dehydration in aestivating animals.
• 3.3. Plasma lactate levels of aestivating animals were low, averaging 1.99 mmol/l, consistent with aerobic rather than anaerobic metabolism having sustained their long period under ground.
• 4.4. No evidence was seen of dramatic physiological specialization. Aestivation in this species is interpreted as a primarily behavioural adaptation, made possible by typically reptilian abilities to tolerate a wide range in plasma electrolytes and to survive long periods without feeding.

     

Partial purification of rat liver cytoplasmic acetyl-CoA synthetase; Characterization of some properties

• 1.1. Rat liver cytoplasmic acetyl-CoA synthetase was partially purified (purification factor = 23, yield = 30%).
• 2.2. The apparent K_ms for acetate, coenzyme A, ATP and MgCl₂ were determined and found to be 52.5 μM, 50.5 μM, 570 μM and 1.5 mM, respectively.
• 3.3. The partially-purified enzyme showed a low affinity for short-chain carbon substrates other than acetate.
• 4.4. The properties of the partially-purified enzyme were compared with those of enzymes from other sources.

     

Evidence that protein kinase C is involved in regulating glucose transport in the adipocyte

• 1.1. The role of protein kinase C in the mechanism of stimulation of glucose transport in rat adipocytes was investigated.
• 2.2. Glucose transprt was stimulated by dioleoylglycerol (DOG), tetradecanoyl phorbol acetate (TPA) and phospholipase C (PLC).
• 3.3. Agents that inhibit protein kinase C (polymyxin B, gossypol and quercitin) also inhibited glucose transport that had been stimulated by DOG, TPA, PLC and insulin.

     

Anaerobic respiration in latex ofHevea brasiliensis substrate and limiting factors

The site of anaerobic respiration in the latex is the serum. The main respiratory substrate is fructose. The CO₂ formation in serum is increased by additional fructose on the average about 2.5–3 times. Glucose does not influence CO₂ evolution by serum but slightly increases O₂ consumption. With respect to sugars, latex serum contains essentially only sucrose and a low amount of raffinose. During the incubation of serum sucrose is hydrolysed, the fructose component is immediately utilized in respiration and glucose accumulates. The rate of CO₂ formation in latex as influenced by fructose is negatively related to the rubber content of the latex. Latex with a high rubber content reacts only slightly or not at all on additional fructose. The main limiting factors of latex respiration and sugar utilization are the following:

1. The deficiency of substrate, due to low activity of β-fructofuranosidase.
2. The rate of glucose phosphorylation (D'Auzac, Jacob 1967).
3. Presumably the low activity of phosphoglucoisomerase.
4. The rubber content of the latex.
5. The concentration of CO₂ in latex; this factor may be important in vivo, in the laticiferous system.

     

Distribution of opine dehydrogenases and lactate dehydrogenase activities in marine animals

• 1.1. Opine dehydrogenases (OpDHs) and lactate dehydrogenase (LDH) activities were determined in various marine animals. OpDHs were detected in six marine invertebrate phyla; Porifera, Coelenterata, Annelida, Mollusca, Arthropoda and Echinodermata in phylogenic sequence.
• 2.2. Among several OpDHs, tauropine dehydrogenase (TaDH) occurred widely in marine invertebrates, from Porifera to Echinodermata.
• 3.3. With a few exceptions, total OpDHs activities exceeded that of LDH activity in the marine invertebrates investigated.
• 4.4. With respect to anaerobic glycolysis, OpDHs are indicated to play an important role in phylogenically lower invertebrates, whereas LDH is more important in higher animals.