Acute tolerance and metabolic responses of Chinese mitten crab (Eriocheir sinensis) juveniles to ambient nitrite

The lethal concentration of nitrite to the Chinese mitten crab Eriocheir sinensis was tested by exposing the animals to 17.78, 23.71, 31.62, 42.17, and 56.23 mg NaNO2 L(-1) at 20 degrees C for 24, 48, 72, and 96 h. The corresponding LC50 value for each time exposure was 43.87 (38.70-51.70), 40.24 (34.88-46.01), 38.87 (33.72-46.01) and 38.87 (33.72-46.01) mg NaNO2 L(-1) or 29.25 (25.80-34.47), 26.83 (23.25-30.67), 25.91(22.48-30.67), 25.91(22.48-30.67) mg NO2-N L(-1), respectively. The physiological response of the crab to nitrite toxicity was further investigated by exposing the crab to 0, 10, 20, 30 and 40 mg NaNO2 L(-1) for 2 d. The changes of nitrogenous compounds in haemolymph, oxyhemocyanin and metabolism were measured at 3, 6, 24 and 48 h upon exposure. Haemolymph nitrite was significantly enhanced by the increase of nitrite from 10 to 40 mg NaNO2 L(-1) during the 2-day exposure. The concentrations of nitrate, urea and glutamate in haemolymph increased concomitantly with the exposing time and ambient nitrite levels, suggesting that the formation of nitrate, urea and glutamine may be the possible end products of nitrite detoxification in crabs. The diffusion of nitrite caused a reduction of oxyhemocyanin, resulting to hypoxia in tissues. Under a hypoxia condition, crabs increased energy demand for metabolism as indicated by the elevated levels of glucose and lactate in haemolymph. Our data showed that ambient nitrite could affect oxygen carrying capacity through oxyhemocyanin reduction and the increase of energy catabolism in crabs. This study suggests that nitrite could be detoxified through the pathway of nitrate, urea and glutamine formation in crabs.     

重组CHO细胞培养过程中氨对细胞代谢的影响

研究了重组CHO细胞批培养过程中,氨浓度对细胞的葡萄糖、谷氨酰胺及其它氨基酸代谢的影响。表明,细胞对葡萄糖和谷氨酰胺的得率系数随着氨浓度的增加而降低,起始氨浓度为566mmol/L的批培养过程与起始氨浓度为021mmol/L的批培养过程相比,细胞对葡萄糖和谷氨酰胺的得率系数分别下降了78%和74%,细胞对其它氨基酸的得率系数也分别下降了50%～70%。氨浓度的增加明显地改变了细胞的代谢途径,葡萄糖代谢更倾向于厌氧的乳酸生成。在谷氨酰胺的代谢过程中,谷氨酸经谷氨酸脱氢酶进一步生成α酮戊二酸的过程受到了氨的抑制,而氨对谷氨酸经谷氨酸转氨酶反应生成α酮戊二酸的过程有促进作用,但总体上谷氨酸进一步脱氨生成α酮戊二酸的反应受到了氨的限制。     

Ammonia Intoxication: Effects on Cerebral Cortex and Spinal Cord

The effect of an acute systemic ammonia intoxication on the metabolic states of the cerebral cortex and the spinal cord of the same animal was studied in the cat. The intravenous infusion of ammonium acetate (2 and 4 mmol/kg body weight/30 min) increased the gross levels of tissue NH4+, glutamine, glutamine/glutamate ratio, lactate, and the lactate/pyruvate ratio in the cerebral cortex and the spinal cord. Pyruvate increased, but significantly only in the spinal cord; aspartate decreased, but significantly only in the cerebral cortex. The infusion of ammonium acetate did not significantly change the levels of phosphocreatine, ATP, ADP, AMP, total adenine nucleotides, adenylate energy charge, glucose, glutamate, alpha-ketoglutarate, and malate in either tissue. The changes of NH4+, glutamine, and lactate levels as well as glutamine/glutamate and lactate/pyruvate ratios in the spinal cord correlated significantly with the corresponding changes of these metabolites in the cerebral cortex. Thus, cerebral cortex and spinal cord show certain specific and comparable metabolic changes in response to a systemic ammonia intoxication. The effect of ammonia intoxication on the increases of glutamine and lactate levels is discussed.     

Methylparathion, carbaryl and aldrin impact on nitrogen metabolism of prawn, Penaeus indicus

Changes in hepatopancreas, muscle and gill tissue nitrogen metabolic profiles were studied in a penaeid prawn, Penaeus indicus, following its exposure to sublethal concentrations of methylparathion, carbaryl and aldrin. In all the insecticide exposed prawn tissues, Ammonia levels were significantly increased and a shift in the nitrogen metabolism towards the synthesis of urea and glutamine was observed. Inhibition of glutamate oxidation to ammonia and alpha-ketoglutarate by glutamate dehydrogenase suggests a mechanism whereby hyperammonemia is reduced by minimizing the addition of further ammonia to the already existing elevated ammonia pool. Increased alanine and aspartate aminotransferases demonstrates the onset of gluconeogenesis. Mechanisms to detoxify the ammonia by enhancing the synthesis of urea and glutamine at the cellular level was observed in the selected tissues pave way for the survivability of prawns in insecticide polluted environs.     

Effects of high temperatures on functional responses of haemocytes in the clam Chamelea gallina

The effects of high temperatures on the clam, Chamelea gallina, generally recognised as a low tolerant bivalve species, were studied by evaluating some functional responses of the haemocytes. The animals were kept for 7days at 20, 25 and 30 degrees C and total haemocyte count (THC), phagocytosis, lysozyme activity (in both haemocyte lysate and cell-free haemolymph), activity and expression of the antioxidant enzyme superoxide dismutase (SOD) (in both haemocyte lysate and cell-free haemolymph) were chosen as biomarkers of exposure to high temperatures. The survival-in-air test was also performed. During the experiment, the clams showed differing burrowing behaviour: the animals kept at 20 and 25 degrees C burrowed completely, whereas at 30 degrees C the clams progressively emerged from the sediment and then remained on the surface. The highest temperature significantly increased THC, whereas it decreased the phagocytic activity of haemocytes. The haemocyte size frequency distribution in clams kept at 30 degrees C showed that the cell population of about 8-10microm was markedly reduced compared to clams kept at 20 and 25 degrees C. In clams maintained at 25 degrees C, lysozyme activity was significantly increased in haemocyte lysate, whereas it was markedly decreased in cell-free haemolymph. Total SOD activity significantly decreased in haemocytes from clams held at 30 degrees C whereas it increased in cell-free haemolymph from clams held at 25 degrees C and 30 degrees C. A significant decrease in haemocyte Mn-SOD and Cu/Zn-SOD activities was found with increasing temperature. In cell-free haemolymph, the highest Mn-SOD activity was recorded at 30 degrees C, whereas the Cu/Zn-SOD activity showed no significant changes in clams maintained at different temperatures. SOD isoform expression exhibited different patterns in haemocyte lysate and cell-free haemolymph. The resistance to air exposure of clams kept at 30 degrees C was shown to decrease significantly, LT(50) values fell from 6days in clams kept at 20 degrees C and 25 degrees C to 4days in those kept at 30 degrees C.     

Changes of haemocyanin,protein and free amino acid levels in the haemolymph of Penaeus japonicus exposed to ambient ammonia

Haemolymph ammonia-N of Penaeus japonicus (15.6 ± 2.17 g) increased with increased ambient ammonia-N, as they were exposed individually in 30 ppt seawater to 0.003 (control), 0.367, 0.731, 1.439 and 3.665 mmol/1 ammonia-N after 24 hr. Ammonia-N excretion was inhibited and net ammonia-N uptake occurred, as shrimps were exposed to 0.367 mmol/1 ammonia-N or greater. Haemocyanin and protein levels in the haemolymph of shrimp decreased, whereas free amino acid levels increased with increased ambient ammonia-N in the range of 0.003–1.439 mmol/1 ammonia-N. Exposure of shrimp to ambient ammonia-N at 1.439 mmol/1 caused accumulation of haemolymph ammonia and urea, and caused catabolism of haemocyanin and protein to free amino acids. Urea, taurine and glutamine are the major organic constituents in the haemolymph of shrimp under ammonia stress.     

Effects of ammonia and lactate on hybridoma growth, metabolism, and antibody production

The influence of ammonia and lactate on cell growth, metabolic, and antibody production rates was investigated for murine hybridoma cell line 163.4G5.3 during batch culture. The specific growth rate was reduced by one-half in the presence of an initial ammonia concentration of 4 mM. Increasing ammonia levels accelerated glucose and glutamine consumption, decreased ammonia yield from glutamine, and increased alanine yield from glutamine. Although the amount of antibody produced decreased with increasing ammonia concentration, the specific antibody productivity remained relatively constant around a value of 0.22 pg/cell-h. The specific growth rate was reduced by one-half at an initial lactate concentration of 55 mM. Although specific glucose and glutamine uptake rates were increased at high lacatate concentration, they showed a decrease after making corrections for medium osmolarity. The yield coefficient of lactate from glucose decreased at high lactate concentrations. A similar decrease was observed for the ammonia yield coefficient from glutamine. At elevated lactate concentrations, specific antibody productivities increased, possibly due to the increase in medium osmolarity. The specific oxygen uptake rate was insensitive to ammonia and lactate concentrations. Addition of ammonia and lactate increased the calculated metabolic energy production of the cells. At high ammonia and lactate, the contribution of glycolysis to total energy production increased. Decreasing external pH and increasing ammonia concentrations caused cytoplasmic acidification. Effect of lactate on intracellular pH was insignificant, whereas increasing osmolarity caused cytoplasmic alkalinization.     

The metabolic response of the kidney to acute sodium lactate alkalosis

In vivo studies were performed in the dog to verify if sodium lactate had an important effect on the metabolism of glutamine by the kidney. The animals were infused with 0.6 M sodium lactate to induce acute metabolic alkalosis with plasma bicarbonate of 29.7 mM. During these experiments, it was demonstrated that the renal uptake of glutamine increased by 46%, while the renal production of ammonia was unchanged. The renal production of alanine rose from 6.0 to 16.8 mumol/min. Plasma concentration of lactate increased from 1.3 to 19.2 mM, while that of pyruvate increased from 0.075 to 0.454 mM. In the renal tissue, alpha-ketoglutarate, malate, oxaloacetate, lactate, pyruvate, citrate, and alanine increased significantly. Similar changes were found in the liver and skeletal muscle. The observed changes are best described by transamination of pyruvate and glutamate under the influence of alanine aminotransferase (GPT). It can be calculated that this reaction was responsible for 76% of the production of ammonia from glutamine, the latter being necessary to provide glutamate for the synthesis of alanine. Dogs infused with 0.3 M sodium bicarbonate instead of sodium lactate with the same degree of acute metabolic alkalosis, showed a depression of 40% in the renal uptake of glutamine with a 38% decrease in renal ammoniagenesis and a 20% fall in the production of alanine. The present studies demonstrate that the production of ammonia from glutamine is not necessarily related to changes in acid-base balance, but may be associated with biochemical alterations related to the synthesis of alanine by the kidney.     

A 15N-n.m.r. study of cerebral, hepatic and renal nitrogen metabolism in hyperammonaemic rats.

1. Rats were infused with 15NH4+ or L-[15N]alanine to induce hyperammonaemia, a potential cause of hepatic encephalopathy. HClO4 extracts of freeze-clamped brain, liver and kidney were analysed by 15N-n.m.r. spectroscopy in combination with biochemical assays to investigate the effects of hyperammonaemia on tissue concentrations of ammonia, glutamine, glutamate and urea. 2. 15NH4+ infusion resulted in a 36-fold increase in the concentration of blood ammonia. Cerebral glutamine concentration increased, with 15NH4+ incorporated predominantly into the gamma-nitrogen atom of glutamine. Incorporation into glutamate was very low. Cerebral ammonia concentration increased 5-10-fold. The results suggest that the capacity of glutamine synthetase for ammonia detoxification was saturated. 3. Pretreatment with the glutamine synthetase inhibitor L-methionine DL-sulphoximine resulted in 84% inhibition of [gamma-15N]glutamine synthesis, but incorporation of 15N into other metabolites was not observed. The result suggests that no major alternative pathway for ammonia detoxification, other than glutamine synthetase, exists in rat brain. 4. In the liver 15NH4+ was incorporated into urea, glutamine, glutamate and alanine. The specific activity of 15N was higher in the gamma-nitrogen atom of glutamine than in urea. A similar pattern was observed when [15N]alanine was infused. The results are discussed in terms of the near-equilibrium states of the reactions involved in glutamate and alanine formation, heterogeneous distribution in the liver lobules of the enzymes involved in ammonia removal and their different affinities for ammonia. 5. Synthesis of glutamine, glutamate and hippurate de novo was observed in kidney. Hippurate, as well as 15NH4+, was contributed by co-extracted urine. 6. The potential utility and limitations of 15N n.m.r. for studies of mammalian metabolism in vivo are discussed.     

Calcium-ion transport by intact synaptosomes. Intrasynaptosomal compartmentation and the role of the mitochondrial membrane potential.

1. The pathways and the fate of glutamate carbon and nitrogen were investigated in isolated guinea-pig kidney-cortex tubules. 2. At low glutamate concentration (1 mM), the glutamate carbon skeleton was either completely oxidized or converted into glutamine. At high glutamate concentration (5 mM), glucose, lactate and alanine were additional products of glutamate metabolism. 3. At neither concentration of glutamate was there accumulation of ammonia. 4. Nitrogen-balance calculations and the release of 14CO2 from L-[1-14C]glutamate (which gives an estimation of the flux of glutamate carbon skeleton through alpha-oxoglutarate dehydrogenase) clearly indicated that, despite the absence of ammonia accumulation, glutamate metabolism was initiated by the action of glutamate dehydrogenase and not by transamination reactions as suggested by Klahr, Schoolwerth & Bourgoignie [(1972) Am. J. Physiol. 222, 813-820] and Preuss [(1972) Am. J. Physiol. 222, 1395-1397]. Additional evidence for this was obtained by the use of (i) amino-oxyacetate, an inhibitor of transaminases, which did not decrease glutamate removal, or (ii) L-methionine DL-sulphoximine, an inhibitor of glutamine synthetase, which caused an accumulation of ammonia from glutamate. 5. Addition of NH4Cl plus glutamate caused an increase in both glutamate removal and glutamine synthesis, demonstrating that the supply of ammonia via glutamate dehydrogenase is the rate-limiting step in glutamine formation from glutamate. NH4Cl also inhibited the flux of glutamate through glutamate dehydrogenase and the formation of glucose, alanine and lactate. 6. The activities of enzymes possibly involved in the glutamate conversion into pyruvate were measured in guinea-pig renal cortex. 7. Renal arteriovenous-difference measurements revealed that in vivo the guinea-pig kidney adds glutamine and alanine to the circulating blood.     

Benzoate stimulates glutamate release from perfused rat liver.

In isolated perfused rat liver, benzoate addition to the influent perfusate led to a dose-dependent, rapid and reversible stimulation of glutamate output from the liver. This was accompanied by a decrease in glutamate and 2-oxoglutarate tissue levels and a net K+ release from the liver; withdrawal of benzoate was followed by re-uptake of K+. Benzoate-induced glutamate efflux from the liver was not dependent on the concentration (0-1 mM) of ammonia (NH3 + NH4+) in the influent perfusate, but was significantly increased after inhibition of glutamine synthetase by methionine sulphoximine or during the metabolism of added glutamine (5 mM). Maximal rates of benzoate-stimulated glutamate efflux were 0.8-0.9 mumol/min per g, and the effect of benzoate was half-maximal (K0.5) at 0.8 mM. Similar Vmax. values of glutamate efflux were obtained with 4-methyl-2-oxopentanoate, ketomethionine (4-methylthio-2-oxobutyrate) and phenylpyruvate; their respective K0.5 values were 1.2 mM, 3.0 mM and 3.8 mM. Benzoate decreased hepatic net ammonia uptake and synthesis of both urea and glutamine from added NH4Cl. Accordingly, the benzoate-induced shift of detoxication from urea and glutamine synthesis to glutamate formation and release was accompanied by a decreased hepatic ammonia uptake. The data show that benzoate exerts profound effects on hepatic glutamate and ammonia metabolism, providing a new insight into benzoate action in the treatment of hyperammonaemic syndromes.     

Ammonia effects on pyruvate/lactate production in astrocytes--interaction with glutamate

Ammonia exerts a multitude of metabolic and non-metabolic effects on brain tissue. In the present communication we have investigated its effect on lactate production rates, pyruvate production rates and pyruvate/lactate ratios in mouse cerebrocortical astrocytes and neurons in primary cultures. No effects were found in neurons. All three parameters were affected by ammonia in astrocytes, but less potently and to a smaller degree in cells that had been treated with dibutyryl cyclic AMP (morphologically differentiated cells) than in untreated cells (morphologically undifferentiated cells). In the differentiated cells ammonia had virtually no effect up to a concentration of 1.0 mM, but at 3.0 mM it increased lactate production and decreased pyruvate/lactate ratio significantly. In the undifferentiated cells ammonia greatly increased lactate accumulation (by 80% at 3.0 mM) and it inhibited pyruvate accumulation (by 40% at 3.0 mM). It thereby reduced the pyruvate/lactate ratio progressively within the entire range 0.1-3.0 mM ammonia. In support of the hypothesis that the ammonia-induced reduction of pyruvate/lactate ratio is secondary to depletion of cellular glutamate by formation of glutamine (and glutathione) and a resulting interruption of the malate-aspartate shuttle (MAS), the addition of glutamate to the incubation medium significantly diminished the ammonia-induced reduction of pyruvate/lactate ratio, whereas it had no effect on the increased lactate production. It is discussed that MAS interruption may have additional consequences in astrocytes.     

Effects of chronic exposure to ammonia on glutamate and glutamine interconversion and compartmentation in homogeneous primary cultures of mouse astrocytes

Accumulation of radioactivity was studied in primary cultures of mouse astrocytes as a function of time of exposure (4–60 min) to 50 M glutamate and 200 M glutamine (initial concentrations), of whicheither glutamateor glutamine was¹⁴C-labeled. Both the glutamate pool and the glutamine pool were compartmentalized. Initially, by far the major intracellular glutamate pool (90%) was derived from extracellular glutamate and could be converted to glutamine. This allowed a rather accurate determination of metabolic flux from glutamate to glutamine, which under control conditions amounted to 2.0–2.2 nmol/min per mg protein. After chronic exposure to 3 mM ammonia for 3 days this flux was significantly increased to 3.1–3.6 nmol/min per mg protein. Acute exposure to ammonia caused a smaller, apparent increase, which was not statistically significant. The glutamine content was compartmentalized at all stages of the incubation. It consisted of at least two different pools. One of these was accessible to extracellular glutamine and could be converted to intracellular glutamate (constituting a sizeable fraction of the total glutamate pool after longer incubation), whereas the other constituted endogenously derived glutamine, formed from accumulated glutamate. The specific activity of the precursor pool for glutamate synthesis could not beaccurately determined and relatively exact fluxes therefore not be calculated. There was, however, no evidence that chronic exposure to ammonia decreases the rate of glutamine hydrolysis.     

The urea cycle in the liver of arthritic rats

The urea cycle in the liver of adjuvant-induced arthritic rats was investigated using the isolated perfused liver. Urea production in livers from arthritic rats was decreased during substrate-free perfusion and also in the presence of the following substrates: alanine, alanine + ornithine, ammonia, ammonia + lactate, ammonia + pyruvate and glutamine but increased when arginine and citrulline + aspartate were the substrates. No differences were found with ammonia + aspartate, ammonia + aspartate + glutamate, aspartate, aspartate + glutamate and citrulline. Ammonia consumption was smaller in the arthritic condition when the substance was infused together with lactate or pyruvate but higher when the substance was simultaneously infused with aspartate or aspartate + glutamate. Glucose production tended to correlate with the smaller or higher rates of urea synthesis. Blood urea was higher in arthritic rats (+25.6%), but blood ammonia was lower (–32.2%). Critical for the synthesis of urea from various substrates in arthritic rats seems to be the availability of aspartate, whose production in the liver is probably limited by both the reduced gluconeogenesis and aminotransferase activities. This is indicated by urea synthesis which was never inferior in the arthritic condition when aspartate was exogenously supplied, being even higher when both aspartate and citrulline were simultaneously present. Possibly, the liver of arthritic rats has a different substrate supply of nitrogenous compounds. This could be in the form of different concentrations of aspartate or other aminoacids such as citrulline or arginine (from the kidneys) which allow higher rates of hepatic ureogenesis.     

Alteration of amino acid metabolism in neuronal aggregate cultures exposed to hypoglycaemic conditions

The neuronal effects of glucose deficiency on amino acid metabolism was studied on three-dimensional cultures of rat telencephalon neurones. Transient (6 h) exposure of differentiated cultures to low glucose (0.25 mm instead of 25 mm) caused irreversible damage, as judged by the marked decrease in the activities of two neurone-specific enzymes and lactate dehydrogenase, 1 week after the hypoglycemic insult. Quantification of amino acids and ammonia in the culture media supernatants indicated increased amino acid utilization and ammonia production during glucose-deficiency. Measurement of intracellular amino acids showed decreased levels of alanine, glutamine, glutamate and GABA, while aspartate was increased. Added lactate (11 mm) during glucose deficiency largely prevented the changes in amino acid metabolism and ammonia production, and attenuated irreversible damage. Higher media levels of glutamine (4 mm instead of 0.25 mm) during glucose deprivation prevented the decrease of intracellular glutamate and GABA, while it further increased intracellular aspartate, ammonia production and neuronal damage. Both lactate and glutamine were readily oxidized in these neuronal cultures. The present results suggest that in neurones, glucose deficiency enhances amino acid deamination at the expense of transamination reactions. This results in increased ammonia production and neuronal damage.     

Hepatocyte heterogeneity in the metabolism of amino acids and ammonia.

With respect to hepatocyte heterogeneity in ammonia and amino acid metabolism, two different patterns of sublobular gene expression are distinguished: 'gradient-type' and 'strict- or compartment-type' zonation. An example for strict-type zonation is the reciprocal distribution of carbamoylphosphate synthase and glutamine synthase in the liver lobule. The mechanisms underlying the different sublobular gene expressions are not yet settled but may involve the development of hepatic architecture, innervation, blood-borne hormonal and metabolic factors. The periportal zone is characterized by a high capacity for uptake and catabolism of amino acids (except glutamate and aspartate) as well as for urea synthesis and gluconeogenesis. On the other hand, glutamine synthesis, ornithine transamination and the uptake of vascular glutamate, aspartate, malate and alpha-ketoglutarate are restricted to a small perivenous hepatocyte population. Accordingly, in the intact liver lobule the major pathways for ammonia detoxication, urea and glutamine synthesis, are anatomically switched behind each other and represent in functional terms the sequence of the periportal low affinity system (urea synthesis) and a previous high affinity system (glutamine synthesis) for ammonia detoxication. Perivenous glutamine synthase-containing hepatocytes ('scavenger cells') act as a high affinity scavenger for the ammonia, which escapes the more upstream urea-synthesizing compartment. Periportal glutaminase acts as a pH- and hormone-modulated ammonia-amplifying system in the mitochondria of periportal hepatocytes. The activity of this amplifying system is one crucial determinant for flux through the urea cycle in view of the high Km (ammonia) of carbamoylphosphate synthase, the rate-controlling enzyme of the urea cycle. The structural and functional organization of glutamine and ammonia-metabolizing pathways in the liver lobule provides one basis for the understanding of a hepatic role in systemic acid base homeostasis. Urea synthesis is a major pathway for irreversible removal of metabolically generated bicarbonate. The lobular organization enables the adjustment of the urea cycle flux and accordingly the rate of irreversible hepatic bicarbonate elimination to the needs of the systemic acid base situation, without the threat of hyperammonemia.     

Changes in the haemocyte profile ofSpilostethus hospes (Fab) (Heteroptera: Lygaeidae) in relation to eclosion,sex and mating

Five types of haemocytes have been identified in the haemolymph ofSpilostethus hospes. Their morphology and micrometric measurements have been provided. Changes in the total and differential haemocyte population [total haemocyte count (THC) and differtial haemocyte count (DHC)] as well as in the absolute number of haemocytes in circulation have been assessed in relation to eclosion, sex and mating. The haemogram profile was studied prior to and immediately after eclosion and also prior to and after copulation. Though the THC was not significantly different immediately before and after eclosion, there was a significant increase in total count prior to copulation. Mated females registered an increase in total count but there was no appreciable change in the mated males. Granulocytes were the most abundant of the haemocyte types in both the sexes and mating caused a significant increase in the plasmatocyte count in females. Changes in the blood volume as well as the mitotic activity of the haemocytes is also discussed     

Effect of the antiepileptic drug sodium valproate on glutamine and glutamate metabolism in isolated human kidney tubules

We studied the effects of sodium valproate, a widely used antiepileptic drug and a hyperammonemic agent, on L-[1-14C]glutamine and L-[1-14C]glutamate metabolism in isolated human kidney-cortex tubules. Valproate markedly stimulated glutamine removal as well as the formation of ammonia, 14CO2, pyruvate, lactate and alanine, but it inhibited glucose synthesis; the increase in ammonia formation was explained by a stimulation by valproate mainly of flux through glutaminase (EC 3.5.1.2) and to a much lesser extent of flux through glutamate dehydrogenase (EC 1.4.1.3). By contrast, valproate did not stimulate glutamate removal or ammonia formation, suggesting that the increase in flux through glutamate dehydrogenase observed with glutamine as substrate was secondary to the increase in flux through glutaminase. Accumulation of pyruvate, alanine and lactate in the presence of valproate was less from glutamate than from glutamine. Inhibition by aminooxyacetate of accumulation of alanine from glutamine caused by valproate did not prevent the acceleration of glutamine utilization and the subsequent stimulation of ammonia formation. It is concluded from these data, which are the first concerning the in vitro metabolism of glutamine and glutamate in human kidney-cortex tubules, that the stimulatory effect of valproate is primarily exerted at the level of glutaminase in human renal cortex.     

半边结灌注培养中杂交瘤细胞的生长和代谢

考察了半连续灌注培养中ＷｕＴ３杂交瘤细胞在不同灌注速率下细胞生长的动态变化,培养其中主要基质的消耗和代谢物的生成。当灌注速率Ｄ从１．０／升高到２．０／ｄ升高到２．０／ｄ时,乳酸得率系数Ｙｌａｃ／ｇｌｕ降低１８％,氨得率系数Ｙａｍｍ／ｇｌｎ降低４０％,丙氨酸得率系数Ｙａｌａ／ｇｌｎ升高５８％,甘氨酸得率系数Ｙｇｌｙ／ｇｌｎ基本恒定。说明在灌注速率升高的条件下,细胞会调整代谢机制,丙酮酸和过量的谷氨酸     

The immune response of the desert locust Schistocerca gregaria during mycosis of the entomopathogenic fungus,Metarhizium anisopliae var acridum

Topical application of Metarhizium anisopliae var acridum to the desert locust Schistocerca gregaria resulted in changes in the biochemistry and antimicrobial defenses of the haemolymph. M. anisopliae var acridum colonized the host haemolymph from day two post application. The haemocytes did not attach to, phagocytose or nodulate elements of the fungus. However, the presence of the fungus appeared to stimulate hemocyte aggregation over the first few days of mycosis though the number of aggregates declined subsequently. The total hemocyte count increased two days after application, indicating an overall stimulation of the immune system, but declined to a value below that for uninoculated controls by day four. The differential haemocyte count showed that the initial increase in total haemocyte count was primarily due to a larger number of coagulocytes. After day two consistent declines in cell number were observed for all haemocyte classes in mycosed insects. The activity of the enzyme, phenoloxidase, decreased during the course of infection. However, the converse was true for prophenoloxidase. Lysozyme levels were significantly smaller in infected than control locusts. There was a significant correlation between lysozyme and PO activities when data from mycosed and control insects were combined. The total protein content of the haemolymph decreased during the course of infection.