Seal lungs collapse during free diving: evidence from arterial nitrogen tensions.

Arterial blood nitrogen tensions of free-diving Weddell seals (Leptonychotes weddelli) were measured by attaching a microprocessor-controlled blood pump and drawing samples at depth to determine how these marine mammals dive to great depths and ascend rapidly without developing decompression sickness. Forty-seven samples of arterial blood were obtained from four Weddell seals during free dives lasting up to 23 minutes to depths of 230 meters beneath the sea ice of McMurdo Sound, Antarctica. Peak arterial blood nitrogen tensions of between 2000 and 2500 millimeters of mercury were recorded at depths of 40 to 80 meters during descent, indicating that the seal's lung collapses by 25 to 50 meters. Then arterial blood nitrogen tensions slowly decreased to about 1500 millimeters of mercury at the surface. In a single dive, alveolar collapse and redistribution of blood nitrogen allow the seal to avoid nitrogen narcosis and decompression sickness.

Carbohydrate metabolism in human platelets in a low glucose medium under aerobic conditions.

The metabolism of human platelets has been the subject of investigation for at least three decades, at the level of basic metabolism, and because of the increasing requirement for platelet storage. Platelets are relatively active metabolically and are typical cells in terms of fuels and metabolic pathways. They contain glycogen and utilize glucose and demonstrate aerobic glycolysis and carbohydrate oxidation. Both glycolysis and carbohydrate oxidation contribute significantly to total ATP turnover, so platelets are an ideal system in which to study the partitioning of carbohydrate metabolism between the two available fuels and the two available pathways, in the presence of adequate oxygen. We have designed a system whereby we can study carbohydrate metabolism in relatively pure human platelets, under sterile conditions, over long periods. The system enables us to determine total ATP turnover and, with the aid of a mathematical model, the contribution to this turnover of glycolysis and the oxidation of glucose/glycogen and lactate. When glucose and glycogen are present, most of the glucose and glycogen utilised is converted to lactate, but lactate is being oxidised at this time. When glucose/glycogen stores are exhausted lactate oxidation continues and increases with the result that carbohydrate oxidation accounts for 41% of total ATP turnover over 48 h.

Advising patients to increase fluid intake for treating acute respiratory infections.

BACKGROUND: Acute respiratory infection is a common reason for people to present for medical care. Advice to increase fluid intake is a frequent treatment recommendation. Attributed benefits of fluids include replacing increased insensible fluid losses, correcting dehydration from reduced intake and reducing the viscosity of mucus. However, there are theoretical reasons for increased fluid intake to cause harm. Anti-diuretic hormone secretion is increased in lower respiratory tract infections of various aetiologies. This systematic examination of the evidence sought to determine the benefit versus harm from increasing fluid intake. OBJECTIVES: To answer the following questions. (1) Does recommending increased fluid intake as a treatment for acute respiratory infections improve duration and severity of symptoms? (2) Are there adverse effects from recommending increased fluids in people with acute respiratory infections? (3) Are any benefits or harms related to site of infection (upper or lower respiratory tract) or a different severity of illness? SEARCH STRATEGY: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 2, 2005), MEDLINE (1966 to July Week 1, 2005), EMBASE (1974 to Week 29, 2005), Current Contents (current 5 years) and CINAHL (1982 to July week 3 2005). Reference lists of articles identified were searched, and experts in the relevant disciplines were contacted. SELECTION CRITERIA: Randomised controlled trials (RCTs) that examined the effect of increasing fluid intake in people with acute respiratory infections. DATA COLLECTION AND ANALYSIS: Each author assessed the identified studies to determine eligibility for inclusion. MAIN RESULTS: No RCTs assessing the effect of increasing fluid intake in acute respiratory infections were found. AUTHORS' CONCLUSIONS: There is currently no evidence for or against the recommendation to increase fluids in acute respiratory infections. The implications for fluid management in acute respiratory infections have not been studied in any RCTs to date. Some non-experimental (observational) studies report that increasing fluid intake in acute respiratory infections may cause harm. RCTs need to be done to determine the true effect of this very common medical advice.

Hemoglobin concentrations and blood gas tensions of free-diving Weddell seals.

Arterial blood gas tensions, pH, and hemoglobin concentrations were measured in four free-diving Weddell seals Leptonychotes weddelli. A microprocessor-controlled sampling system enabled us to obtain 24 single and 31 serial aortic blood samples. The arterial O2 tension (PaO2) at rest [78 +/- 13 (SD) Torr] increased with diving compression to a maximum measured value of 232 Torr and then rapidly decreased to 25-35 Torr. The lowest diving PaO2 we measured was 18 Torr just before the seal surfaced from a 27-min dive. A consistent increase of arterial hemoglobin concentrations from 15.1 +/- 1.10 to 22.4 +/- 1.41 g/100 ml (dives less than 17 min) and to 25.4 +/- 0.79 g/100 ml (dives greater than 17 min) occurred during each dive. We suggest that an extension of the sympathetic outflow of the diving reflex possibly caused profound contraction of the Weddell seal's very large spleen (0.89% of body wt at autopsy), although we have no direct evidence. This contraction may have injected large quantities of red blood cells (2/3 of the total) into the seal's central circulation during diving and allowed arterial O2 content to remain constant for the first 15-18 min of long dives. The increase of arterial CO2 tensions during the dive and the compression increase of arterial N2 tensions were also moderated by injecting red blood cells sequestered at ambient pressure. After each dive circulating red blood cells are oxygenated and rapidly sequestered, possibly in the spleen during the first 15 min of recovery.

Host determinants of DNA alkylation and DNA repair activity in human colorectal tissue: O(6)-methylguanine levels are associated with GSTT1 genotype and O(6)-alkylguanine-DNA alkyltransferase activity with CYP2D6 genotype.

There is increasing evidence that alkylating agent exposure may increase large bowel cancer risk and factors which either alter such exposure or its effects may modify risk. Hence, in a cross-sectional study of 78 patients with colorectal disease, we have examined whether (i) metabolic genotypes (GSTT1, GSTM1, CYP2D6, CYP2E1) are associated with O(6)-methyldeoxyguanosine (O(6)-MedG) levels, O(6)-alkylguanine-DNA alkyltransferase (ATase) activity or K-ras mutations, and (ii) there was an association between ATase activity and O(6)-MedG levels. Patients with colon tumours and who were homozygous GSTT1(*)2 genotype carriers were more likely than patients who expressed GSTT1 to have their DNA alkylated (83 versus 32%, P=0.03) and to have higher O(6)-MedG levels (0.178+/-0.374 versus 0.016+/-0.023 micromol O(6)-MedG/mol dG, P=0.04) in normal, but not tumour, DNA. No such association was observed between the GSTT1 genotype and the frequency of DNA alkylation or O(6)-MedG levels in patients with benign colon disease or rectal tumours. Patients with colon tumours or benign colon disease who were CYP2D6-poor metabolisers had higher ATase activity in normal tissue than patients who were CYP2D6 extensive metabolisers or CYP2D6 heterozygotes. Patients with the CYP2E1 Dra cd genotype were less likely to have a K-ras mutation: of 55 patients with the wild-type CYP2E1 genotype (dd), 23 had K-ras mutations, whereas none of the 7 individuals with cd genotype had a K-ras mutation (P=0.04). No other associations were observed between GSTT1, GSTM1, CYP2D6 and CYP2E1 Pst genotypes and adduct levels, ATase activity or mutational status. O(6)-MedG levels were not associated with ATase activity in either normal or tumour tissue. However, in 15 patients for whom both normal and tumour DNA contained detectable O(6)-MedG levels, there was a strong positive association between the normal DNA/tumour DNA adduct ratio and the normal tissue/tumour tissue ATase ratio (r(2)=0.66, P=0.001). These results indicate that host factors can affect levels both of the biologically effective dose arising from methylating agent exposure and of a susceptibility factor, the DNA repair phenotype.

Effects of urea on M4-lactate dehydrogenase from elasmobranchs and urea-accumulating Australian desert frogs.

We measured the effect of urea on M4-lactate dehydrogenase (M4-LDH) from elasmobranchs and Australian desert frogs (urea accumulators) and from two animals that do not accumulate urea, the axolotl and the rabbit. An analysis of the effect of urea on the Kd(NADH), V, V/K(m(prr)) and V/K(m(NADH)) shows that in all cases the major effect of urea was on the binding of pyruvate, which fits with data in the literature that show that urea acts as a competitive inhibitor of LDH. The characteristics of the elasmobranch enzymes are consistent with a proposed adaptation model, but the situation for the enzymes from the aestivating frogs is equivocal. Urea (400 mM) had less effect on the K(m(prr)) of M4-LDH from the urea accumulators than it did on the non-accumulators, suggesting a general adaptation and that the enzyme produced by the aestivating frogs (urea accumulators) is kinetically different from that of non-aestivating frogs (non-accumulators). A new approach is used to characterize the overall pattern of adaptation to urea. The pattern is similar in an enzyme from an elasmobranch and an aestivating frog despite the temporary presence of urea in the latter and the phylogenetic difference between these animals.

The hare and the tortoise: metabolic strategies in cardiac and skeletal muscles of the skink and the chameleon.

Two lizards--a skink capable of fast short dashes, and a chameleon, incapable of fast movement--have been studied to determine the degree of metabolic diversity that exists in this group of reptiles. Oxygen uptake measurements, skeletal muscle histochemistry, and enzyme and metabolite levels in cardiac and skeletal muscles reveal that the skink has a higher metabolic potential, both aerobic and anaerobic, than the chameleon. The difference, however, is not as large as is indicated by the behaviors of the two lizards. Levels of citrate synthase and B-hydroxybutaryl CoA dehydrogenase in the hearts of both the lizards are high and indicate mammalian-level metabolic capabilities.

Metabolic depression in animals: physiological perspectives and biochemical generalizations.

Depression of metabolic rate has been recorded for virtually all major animal phyla in response to environmental stress. The extent of depression is usually measured as the ratio of the depressed metabolic rate to the normal resting metabolic rate. Metabolic rate is sometimes only depressed to approx. 80% of the resting value (i.e. a depression of approx. 20% of resting); it is more commonly 5-40% of resting (i.e. a depression of approx. 60-95% of resting); extreme depression is to 1% or less of resting, or even to an unmeasurably low metabolic rate (i.e. a depression of approx. 99-100% of resting). We have examined the resting and depressed metabolic rate of animals as a function of their body mass, corrected to a common temperature. This allometric approach allows ready comparison of the absolute level of both resting and depressed metabolic rate for various animals, and suggests three general patterns of metabolic depression. Firstly, metabolic depression to approx. 0.05-0.4 of rest is a common and remarkably consistent pattern for various non-cryptobiotic animals (e.g. molluscs, earthworms, crustaceans, fishes, amphibians, reptiles). This extent of metabolic depression is typical for dormant animals with 'intrinsic' depression, i.e. reduction of metabolic rate in anticipation of adverse environmental conditions but without substantial changes to their ionic or osmotic status, or state of body water. Some of these types of animal are able to survive anoxia for limited periods, and their anaerobic metabolic depression is also to approx. 0.05-0.4 of resting. Metabolic depression to much less than 0.2 of resting is apparent for some 'resting', 'over-wintering' or diapaused eggs of these animals, but this can be due to early developmental arrest so that the egg has a low 'metabolic mass' of developed tissue (compared to the overall mass of the egg) with no metabolic depression, rather than having metabolic depression of the entire cell mass. A profound decrease in metabolic rate occurs in hibernating (or aestivating) mammals and birds during torpor, e.g. to less than 0.01 of pre-torpor metabolic rate, but there is often no intrinsic metabolic depression in addition to that reduction in metabolic rate due to readjustment of thermoregulatory control and a decrease in body temperature with a concommitant Q10 effect. There may be a modest intrinsic metabolic depression for some species in shallow torpor (to approx. 0.86) and a more substantial metabolic depression for deep torpor (approx. 0.6), but any energy saving accruing from this intrinsic depression is small compared to the substantial savings accrued from the readjustment of thermoregulation and the Q10 effect. Secondly, a more extreme pattern of metabolic depression (to < 0.05 of rest) is evident for cryptobiotic animals. For these animals there is a profound change in their internal environment--for anoxybiotic animals there is an absence of oxygen and for osmobiotic, anhydrobiotic or cryobiotic animals there is an alteration of the ionic/osmotic balance or state of body water. Some normally aerobic animals can tolerate anoxia for considerable periods, and their duration of tolerance is inversely related to their magnitude of metabolic depression; anaerobic metabolic rate can be less than 0.005 of resting. The metabolic rate of anhydrobiotic animals is often so low as to be unmeasurable, if not zero. Thus, anhydrobiosis is the ultimate strategy for eggs or other stages of the life cycle to survive extended periods of environmental stress. Thirdly, a pattern of absence of metabolism when normally hydrated (as opposed to anhydrobiotic or cryobiotic) is apparently unique to diapaused eggs of the brine-shrimp (Artemia spp., an anostracan crustacean) during anoxia. The apparent complete metabolic depression of anoxic yet hydrated cysts (and extreme metabolic depression of normoxic, hypoxic, or osmobiotic, yet hydrated cysts), is an obvious exception to the above patterns. (ABST

Marathon fatigue: the role of plasma fatty acids, muscle glycogen and blood glucose.

The role of carbohydrate depletion in marathon fatigue was examined in 6 marathon runs. Four of the runs were potentially 'fast-time' marathons and culminated in fatigue. The utilization of carbohydrate, lipid and protein, and plasma concentrations of free fatty acids (FFA), glucose and lactate were measured at intervals throughout the runs. The contribution from protein to energy output was low (1-2%). The utilization of lipid was dependent upon plasma concentrations of FFA, which rose throughout the run. The utilization of carbohydrate mirrored that of FFA and thus fell throughout the run. Fatigue was characterized by a drop in running speed, a drop in carbohydrate utilization, an unchanging FFA utilization and a fall in blood glucose. The fall in blood glucose was not seen in the non-fatigued runners. These results are consistent with carbohydrate depletion being the cause of fatigue. The implications of these data are that lipid is the preferred fuel, but is rate-limiting, and that carbohydrate depletion, even though it causes fatigue, ensures an optimal-time marathon.

Role of dehydrogenase competition in metabloic regulation. The case of lactate and alpha-glycerophosphate dehydrogenases.

Many tissues expressing capacities for both anaerobic and aerobic glycolysis contain significant amounts of both lactate dehydrogenase and alpha-glycerophosphate dehydrogenase. Since the first serves in oxidation-reduction balance during anaerobic metabolism, while the second serves in the alpha-glycerophosphate cycle during aerobic metabolism, a provision seemed to be made (through competition for coenzyme) to encourage relatively exclusive function of either one or the other dehydrogenase. Competition for coenzyme was found to depend upon the isoenzyme form of each dehydrogenase (which determines the sensitivity of each reaction to modulators) and the concentration of two key metabolites, alpha-glycerophosphate and creatine phosphate, which differentially influence alpha-glycerophosphate dehydrogenases and lactate dehydrogenases. The sensitivities of various dehydrogenase isoenzymes to these modulators correlated well with their expected roles in the tissue of origin.

The role of the Crabtree effect and an endogenous fuel in the energy metabolism of resting and proliferating thymocytes.

Rat thymocytes have been used to characterize the changes in energy metabolism that occur as cells undergo a resting/proliferation transition. In the resting state, anaerobic ATP production accounts for only 4% of ATP turnover. The remainder is fueled by the oxidation of a mixture of an unidentified endogenous fuel (62%), glucose (18%) and glutamine (16%). 48 h after mitogen stimulation, the ATP turnover has increased twofold. In these proliferating cells, glucose inhibits oxygen consumption by 58%, indicating a profound Crabtree effect which is not present in resting cells. Consequently, proliferating cells, in the presence of glucose and glutamine, fuel the majority (61%) of ATP turnover anaerobically, producing lactate from glucose. The development of a Crabtree effect may be the result of the 8-10-fold increase in glycolytic enzyme activities which occurs with proliferation. Possible advantages of such a proliferative metabolism are a sparing of endogenous fuel, and a minimizing of oxidative metabolism, with its concurrent production of free radicals.

Do Australian desert frogs co-accumulate counteracting solutes with urea during aestivation?

Australian desert frogs of the genera Neobatrachus, Cyclorana and Heleioporus experience significant dehydration, and iono- and osmoconcentration, during aestivation in the laboratory and accumulate substantial amounts of urea (100-200 mmol)(l-1). We expected a priori that aestivating frogs probably would not need to accumulate balancing osmolytes but would accumulate trimethylamine oxide (TMAO) or betaine as counteracting solutes to urea. These aestivating frogs did not co-accumulate a substantial quantity of any particular balancing osmolyte or counteracting solute, such as a methylamine [TMAO, trimethylamine amine (TMA), betaine, sarcosine, glycerophosphorylcholine (GPC)] or polyol (inositol, mannitol, sorbitol) in plasma or muscle relative to urea accumulation. However, for aestivating frogs, the total concentration of all measured methylamines and polyols (TMAO + TMA + betaine + sarcosine + GPC + inositol) in muscle was approximately 35-45 mmol kg-1, and so it is possible that all of these solutes have a combined counteracting osmolyte role in aestivating frogs at a ratio to urea of approximately 1:2.5, as has been described for elasmobranch fishes. Alternatively, the absence of substantial co-accumulation with urea of any particular solute suggests that aestivating frogs might not require any major extracellular or intracellular counteracting solutes (TMAO, betaine, GPC). The enzyme systems of these aestivating frogs may be insensitive to the perturbing effects of urea, or the perturbing effects of accumulated urea may be a mechanism for metabolic depression, during aestivation.

Controlling the highest lactate dehydrogenase activity known in nature.

In the shipjack, Euthynnus pelamis, white muscle appears to possess a powerful anaerobic capacity as well as a significant carbohydrate based aerobic potential. Lactate dehydrogenase occurs at higher activities than found thus far anywhere else in nature and clearly functions in anaerobic glycolysis. Alpha-glycerophosphate dehydrogenase also occurs in unusually high activities and appears to play a role in aerobic glycolysis. Regulation of these two reactions is accomplished by temperature, pH, and creatine phosphate levels. High temperature, low pH, and low creatine phosphate levels all appear to favor lactate dehydrogenase over alpha-glycerophosphate dehydrogenase; low temperature, high pH, and high creatine-phosphate levels, all expected during the quiescent state in this species, and when metabolism in aerobic, all favor alpha-glycerophosphate dehydrogenase activity.

Fructose formation in stored blood.

At the high glucose concentrations used in the collection and storage of donor blood the activity of the fructose-forming polyol pathway (Reaction I and II) could act to deplete NADPH and thus GSH, thereby exposing the cells to oxidative stress. Fructose levels were found to be high in red cells and the supernatant plasma of blood collected into CP2D, which contains 258 mM glucose. Elevated fructose was not produced by the polyol pathway, but was formed by the autoclaving process. A high fructose concentration sufficient to account for the fructose in donor red cells was also found in the CP2D anticoagulant and in samples of autoclaved glucose.

Changes in enzyme binding and activity during aestivation in the frog Neobatrachus pelobatoides.

1. The proportion of aldolase and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) associated with the particulate fraction of a cell was measured in aestivating and non-aestivating Neobatrachus pelobatoides. 2. Reduced binding of these enzymes was found in the brain, indicating lower glycolytic flux. This was not correlated to metabolic rate suggesting that glycolytic rate was reduced in this tissue in the early stages of aestivation, possibly due to a change in fuel use. 3. Measurement of total enzyme levels showed that the liver of aestivating frogs had less GAPDH and less aldolase than non-aestivating frogs.

A complete platelet system for metabolic studies: pure, defined, and viable over 8 hours.

We have been using a human platelet preparation to investigate various aspects of cellular metabolism. These experiments require a pure, quantitated platelet preparation that is viable for up to 8 h. The purity of the preparation has previously been characterized and we have now assessed its viability over 8 h and developed a simple spectrophotometric counting method. This method of counting results in estimations that are within 6% of those from an electronic cell counter (Coulter). Pure platelets stored in a Hepes physiological saline were resuspended periodically in autologous plasma to assess function over 24 h. The platelets consumed oxygen, changed shape, aggregated, and released dense granule ATP at all times. There was a slow and linear decrease in the various processes with time, ranging from 1.7% per hour for oxygen consumption to 3.8% per hour for percentage aggregation. The preparation is therefore not stable, but the changes with time are small and defined and it represents a useful system for the study of platelet and cell biology.

Types and sources of fuels for platelets in a medium containing minimal added fuels and a low carryover plasma.

The storage of platelets in synthetic media can result in plasma savings and reduced transfusion reactions. Accordingly, a wide range of storage formulations have been developed with the aim of replacing at least a proportion of the plasma in the storage medium. However, the concentrations and types of fuels in the carryover plasma, and the utilization of these fuels by platelets in storage, has not been investigated. We have developed a system which can measure total ATP turnover, and the contribution to total ATP turnover by the oxidation of various fuels and by lactate production, in a bag of partially purified platelets in a buffered saline with minimal carryover citrate phosphate double dextrose (CP2D) plasma. Carryover plasma was about 1% and the final platelet suspension contained, on average, 0.62 mM glucose, 9.6 mg/l free fatty acids, 32 mg/l triglycerides and 0.23 mM total amino acids. The oxidation of carbohydrate (glucose, glycogen and lactate) accounted for 60% of total ATP turnover. The platelets also produced lactate (<6% of total ATP turnover) and consumed free fatty acids and amino acids/proteins (15.2% of total ATP turnover). Therefore we have identified the fuels that account for about 80% of oxygen consumption and ATP turnover by platelets in a medium with low carryover plasma. The implications of these data for storage strategies are discussed.

Glucose is essential for proliferation and the glycolytic enzyme induction that provokes a transition to glycolytic energy production.

A transition from aerobic to anaerobic metabolism occurs as mitogen-activated thymocytes undergo proliferation. Glucose utilization and lactate formation increases 18- and 38-fold, respectively, during proliferation. The absolute amount of 14CO2 production by pyruvate dehydrogenase remains constant, while 14CO2 production by the tricarboxylic acid cycle is reduced during transition from a resting to a proliferating state. Addition of 2,4-dinitrophenol, an agent uncoupling oxidative phosphorylation, and phenacinemethosulfate, an electron acceptor, provide evidence that the reduction of glucose oxidation in proliferating thymocytes is caused neither by limitation of the tricarboxylic acid cycle itself nor by an insufficient supply of ADP. Our data suggest that enhanced cytosolic regeneration of NAD+ by induction of the glycolytic enzymes during proliferation effectively competes with NADH transport and its subsequent oxidation in the mitochondria. Mitogen-stimulated rat thymocytes cultured in a conventional medium containing glucose induce their glycolytic enzymes 8-10-fold in the S phase of the cell cycle and divide within a culture period of 72 h. Replacement of glucose by glutamine, glutamine and ribose, or glutamine and uridine prevents glycolytic enzyme induction and thymocyte proliferation. The effect of glucose on glycolytic enzyme induction cannot be mimicked by 3-O-methylglucose or 2-deoxyglucose. In conclusion, glucose is required for proliferation and the glycolytic enzyme induction that mediates the transition from oxidative to glycolytic energy production during the G1/S transition of rat thymocytes.