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PubMed2002

Reduced atmospheric CO2 inhibits nitrogen mobilization in Festuca rubra.

In defoliated grasses, where photosynthesis is reduced due to removal of leaf material, it is well established that remobilization of nitrogen occurs from both older remaining leaves and roots towards the younger growing leaves. In contrast, little is known about the movement of nitrogen within intact grass plants experiencing prolonged inhibition of photosynthesis. We tested the following hypotheses in Festuca rubra L. ssp. rubra cv. Boreal: that both reduction of the atmospheric CO2 concentration and defoliation (1) induce mobilization of nitrogen from roots and older leaves towards growing leaves and (2) elicit similar directional change in the abundance of proteins in roots and older leaves relevant to the process of nitrogen mobilization including, glutamine synthetase (GS), EC 6.3.1.2; papain, EC 3.4.22.2; chymopapain, EC 3.4.22.6; ribulose bisphosphate carboxylase/oxygenase (Rubisco), EC 4.1.1.39; and the light harvesting complex of photosystem II (LHCPII). After growth at ambient atmospheric CO2 concentration, plants of F. rubra were subject to atmospheres containing either ambient (350 micro l l-1) or deplete (< 20 micro l l-1) CO2. Concurrently, plants were either left intact or defoliated on one occasion. Steady state 15N labelling coupled with a series of destructive harvests over a 7-day period enabled changes in the nitrogen dynamics of the plants to be established. Proteins pertinent to the process of nitrogen mobilization were quantified by immunoblotting. Irrespective of defoliation, plants in ambient CO2 mobilized nitrogen from older to growing leaves. This mobilization was inhibited by deplete CO2. Greater concentration of Rubisco and reduced chymopapain abundance in older remaining leaves of intact plants, in deplete compared with ambient CO2, suggested the inhibition of mobilization was due to inhibition of protein degradation, rather than to the export of degradation products. Both deplete CO2 and defoliation induced nitrogen mobilization from roots to growing leaves. In plants at ambient CO2, defoliation did not affect nitrogen uptake or its allocation. Therefore in F. rubra nitrogen mobilization can occur independently of any downregulation of nitrogen uptake. This suggests either different signal compounds may act to downregulate uptake and upregulate mobilization, or if one particular signalling compound is used its concentration threshold differs for induction of mobilization and downregulation of uptake. The abundance of the cysteine proteases papain and chymopapain was low in roots suggesting that they were not involved in protein degradation in this tissue.

Journal Article↗

PubMed1996

Carbon and nitrogen allocation in ectomycorrhizal and non-mycorrhizal Pinus sylvestris L. seedlings.

We studied carbon and nitrogen allocation in mycorrhizal and non-mycorrhizal Scots pine (Pinus sylvestris L.) seedlings grown in a semi-hydroponic system with nitrogen as the growth limiting factor. Three ectomycorrhizal fungi were compared: one pioneer species (Thelephora terrestris Ehrh.: Fr.) and two late-stage fungi (Suillus bovinus (L.: Fr.) O. Kuntze, and Scleroderma citrinum Pers.). By giving all plants in each treatment the same amount of readily available nitrogen, we ensured that the external mycelium could not increase the total nitrogen content of the plants, thereby guaranteeing that any change in carbon or nitrogen partitioning was a direct effect of the mycorrhizal infection itself. Carbon and nitrogen partitioning were measured at an early and a late stage of mycorrhizal development, and at a low and a high N addition rate. Although mycorrhizal seedlings had a higher net assimilation rate and a higher shoot/root ratio than non-mycorrhizal seedlings, they had a lower rate of shoot growth. The high carbon demand of the mycobionts was consistent with the large biomass of external mycelia and the increased belowground respiration of the mycorrhizal plants. The carbon cost to the host was similar for pioneer and late-stage fungi. Above- and belowground partitioning of nitrogen was also affected by mycorrhizal infection. The external mycelia of Scleroderma citrinum retained 32% of the nitrogen supplied to the plants, thus significantly reducing nitrogen assimilation by the host plants and consequently reducing their growth rate. By contrast, the external mycelia of T. terrestris and Suillus bovinus retained less nitrogen than the mycelia of Scleroderma citrinum, hence we attributed the decreased growth rates of their host plants to a carbon drain rather than a nitrogen deficiency.

Journal Article↗

PubMed1995

Effects of feeding and confinement on nitrogen metabolism and excretion in the gulf toadfish Opsanus beta

In order to elucidate further the cues for, and the biochemical mechanisms of, the transition to ureogenesis in the gulf toadfish Opsanus beta, experiments on the effects of feeding (i.e. nitrogen loading) were carried out. Baseline nitrogen excretion rates were first measured on solitary toadfish in large water volumes (i.e. unconfined conditions). These nitrogen excretion rates were higher, and had a higher proportion as ammonia (61 %), than previously published 'control' measurements. Feeding of unconfined toadfish elevated total nitrogen excretion approximately threefold, with little change in the proportion of urea versus ammonia. During the first 24 h of confinement of unfed toadfish, absolute levels of urea excretion remained constant while ammonia excretion rates fell to near zero, so that toadfish became 90 % ureotelic. When fed prior to confinement, urea excretion rates remained constant for the first 24 h, and the bulk of the nitrogen was excreted as ammonia (80 %); excretion of the excess dietary nitrogen took up to 48 h to complete. If pre-adapted to confinement and then fed, toadfish excreted only about 55 % of their nitrogenous waste as ammonia, and excretion of excess dietary nitrogen was completed by 24 h. Elevations of hepatic glutamine synthetase (GNS) activities accompanied confinement and were shown to be almost exclusively in the cytosolic compartment and to be correlated with a decrease in the ratio of hepatic levels of glutamate:glutamine. These GNS activity increases also appear to account in part for the decrease in the percentage of ammoniotely in toadfish under conditions of nitrogen loading after confinement. However, additional means of regulating total nitrogen excretion (e.g. changes in protein turnover rates) and the degree of ureogenesis versus ammoniogenesis (e.g. N-acetylglutamate stimulation of carbamoylphosphate synthetase) must be postulated to account fully for changes in nitrogen excretion rates and activation of ureogenesis under some circumstances.

Journal Article↗

PubMed2000

Internal glutamine and glutamate pools in Klebsiella pneumoniae grown under different conditions of nitrogen availability.

Internal pool sizes of glutamine and glutamate in Klebsiella pneumoniae grown under nitrogen limitation or nitrogen sufficiency were measured to study the signal transduction of external nitrogen limitation. K. pneumoniae cells were grown in an anaerobic, ammonium-limited chemostat culture. At a growth rate of 0.217 h(-1), the steady state ammonium concentration in the culture was 55 microm, correlating with repression of the nitrogen fixation (nif) genes. At growth rates below 0.138 h(-1), the ammonium concentration in the culture dropped below 0.5 microm and the nif genes became derepressed. During the transition from nitrogen sufficiency to nitrogen limitation, the internal glutamine pool in K. pneumoniae decreased by a factor of approximately 6. The glutamate pool, however, remained stable. Similarly, in anaerobic batch cultures with different limiting nitrogen sources, the glutamine pool generally decreased by a factor of 7 to 9 when nif gene derepression was achieved. All the limiting nitrogen sources used resulted in decreased growth rates compared with growth under nitrogen excess, suggesting an inverse relationship between glutamine pool size and doubling time. These studies indicate that K. pneumoniae perceives external nitrogen limitation as internal glutamine limitation.

Fermentation↗

PubMed1997

Paradoxical positive nitrogen balance in burn patients receiving high-dose administration of insulin for nutritional care.

BACKGROUND: Nitrogen balance in patients who need high-dose administration of insulin has not been evaluated clinically. The purpose of this study was to compare the difference in nitrogen balance between burn patients who received high-dose administration of insulin and those who did not. METHODS: This study was performed in 19 severely burned adults with no liver or kidney failure. Patients were divided into two groups on the basis of the mean ratio of administered insulin and calorie intake (I/C) for the initial 4 weeks, a high I/C group (n = 9) and a low I/C group (n = 10). There were no significant differences between the two groups regarding age, percentage of area burned, and body weight. Nitrogen balance, blood urea nitrogen, and urine urea nitrogen were measured in all patients. Plasma concentrations of glucose, insulin, glucagon, cortisol, and urinary excretion of 3-methyl-histidine were measured in 12 patients (six in each group). RESULTS: Until day 10 both groups exhibited similar changes in plasma concentrations of glucose, insulin, glucagon, and cortisol. Subsequently, plasma concentrations of insulin and glucagon began to decrease in the low I/C group, whereas a high level was sustained in the high I/C group (p < 0.05). Plasma glucose and cortisol measurements showed no significant differences between the two groups. Blood urea nitrogen levels and urinary excretion of 3-methyl-histidine were not different between the two groups. Urine urea nitrogen excretion in the high I/C group, however, was significantly lower than that in the low I/C group from day 8 (p < 0.05). Thus the high I/C group achieved positive nitrogen balance more quickly than the low I/C group. Paradoxically, however, the high I/C group was at higher risk of septic complications and exhibited higher mortality than the low I/C group (p < 0.05). CONCLUSIONS: These results indicate that an improvement in nitrogen balance, which is accepted as a good thing in the management of critically ill patients, is not necessarily good in the high I/C group and that residual nitrogen was retained within the body in the high I/C group.

Adult↗

PubMed1982

Nitrogen utilization in uremic patients fed by continuous nasogastric infusion.

Patients with severe renal failure were continuously fed an electrolyte-free solution containing oligosaccharides plus 35 g of a mixture of six amino acids and four (or, in one study, five) nitrogen-free analogues via a small-bore nasogastric tube attached to a pump. They also ingested three small meals daily. Total caloric intake averaged 34 kcal/kg (of which 76% was infused). Total nitrogen intake averaged only 3.3 g (of which 68% was infused). Nevertheless, nitrogen balance was positive (average + 1.22 g/day). All components of nitrogen excretion fell to unusually low average values: urea nitrogen appearance, 1.14 g/day; non-urea urinary nitrogen. 0.63 g/day; fecal nitrogen, 0.48 g/day. Nitrogen requirement for balance on this regimen, estimated from linear regression, was only 2.0 g/day. Body weight did not change significantly. Serum albumin and transferrin remained normal. Thus, this regimen induces positive nitrogen balance despite low nitrogen intake.

Aged↗

PubMed1982

Increased ureagenesis and impaired nitrogen use during infusion of a synthetic amino acid formula: a controlled trial.

In a controlled trial conducted to assess the biologic value of High Nitrogen Vivonex, we compared this "elemental" diet with predigested protein--Product MJ7041--and with solid food during eight-day balance periods. Each formula was evaluated in three patients with malabsorption and one without it, by measuring apparent absorption of nitrogen and energy, nitrogen balance, and blood and urinary urea nitrogen. Overall energy and nitrogen absorption in the patients with malabsorption was better with either special diet than with solid food; net intestinal uptake of Vivonex tended to be higher but not consistently so in al patients. However, nitrogen balance differed consistently during the three diets; with solid food and MJ7041, retention of absorbed nitrogen was respectively, nine and 16 times greater than with Vivonex. Moreover, institution of each Vivonex period led to a prompt increase in urea nitrogen--a trend quickly reversed by the alternative diets. Although the mechanism for the impairment of nitrogen use caused by High Nitrogen Vivonex is unknown, its low biologic value and tendency to cause azotemia should be kept in mind.

Adult↗

PubMed1999

Nitrogen management and the future of food: lessons from the management of energy and carbon.

The food system dominates anthropogenic disruption of the nitrogen cycle by generating excess fixed nitrogen. Excess fixed nitrogen, in various guises, augments the greenhouse effect, diminishes stratospheric ozone, promotes smog, contaminates drinking water, acidifies rain, eutrophies bays and estuaries, and stresses ecosystems. Yet, to date, regulatory efforts to limit these disruptions largely ignore the food system. There are many parallels between food and energy. Food is to nitrogen as energy is to carbon. Nitrogen fertilizer is analogous to fossil fuel. Organic agriculture and agricultural biotechnology play roles analogous to renewable energy and nuclear power in political discourse. Nutrition research resembles energy end-use analysis. Meat is the electricity of food. As the agriculture and food system evolves to contain its impacts on the nitrogen cycle, several lessons can be extracted from energy and carbon: (i) set the goal of ecosystem stabilization; (ii) search the entire production and consumption system (grain, livestock, food distribution, and diet) for opportunities to improve efficiency; (iii) implement cap-and-trade systems for fixed nitrogen; (iv) expand research at the intersection of agriculture and ecology, and (v) focus on the food choices of the prosperous. There are important nitrogen-carbon links. The global increase in fixed nitrogen may be fertilizing the Earth, transferring significant amounts of carbon from the atmosphere to the biosphere, and mitigating global warming. A modern biofuels industry someday may produce biofuels from crop residues or dedicated energy crops, reducing the rate of fossil fuel use, while losses of nitrogen and other nutrients are minimized.

Agriculture↗

PubMed2001

Nitrogen exchanges: testing the hypothesis of a country without agricultural production.

Today, finding data on agricultural nitrogen balances is quite easy. Calculations of such balances are carried out by most of the European countries as an indicator of environmental pollution attributable to the agricultural sector. In France, average values of agricultural nitrogen balances show an excess of 1.5 to 2 million tons of nitrogen. This excess is enormous. What would the balance of a country be if agricultural activity were stopped? In the following article, a country (France is used as an example) without agriculture is studied in order to assess its nitrogen balance. Using a previously published model describing nitrogen input and output of a given country, nitrogen flows are identified. Inputs include deposition, fixation, and products not intended for agricultural use. Outputs are reduced to zero if agriculture disappears (in France, agriculture is the only sector exporting products containing nitrogen). All flows are calculated considering the hypothesis of disappearance of agriculture. Nitrogen requirements to feed people and pets in France are estimated based on medical and veterinary data (recommended daily amounts for proteins and/or usual average consumption). Indeed, most of the food that nourishes the French population is produced nationally. If agriculture stops, it will be necessary to import food from foreign countries. Results show an unexpectedly high excess (for a country without agriculture having a structure similar to France: number of human beings and pets) of 1.5 million tons of nitrogen. An attempt to calculate an agricultural balance with the same data gives a result close to 3 million tons. Differences in French agricultural balances found in the literature can mainly be explained by values taken into account for deposition and fixation (values used here are at least 300,000 tons higher than values used by the Organisation for Economic Co-operation and Development). In conclusion, nitrogen excess in agriculture is partly due to social demand; agriculture does not only produce food but also includes many other functions (landscape management, employment, and preservation of culture, for example). As a consequence, efforts that do not involve suppressing agriculture should be made to figure out alternative ways of production.

Agriculture↗

PubMed1964

PEPTIDES AND OTHER NITROGEN SOURCES FOR GROWTH OF BACTEROIDES RUMINICOLA.

Pittman, K. A. (Agricultural Research Service, Beltsville, Md.), and M. P. Bryant. Peptides and other nitrogen sources for growth of Bacteroides ruminicola. J. Bacteriol. 88:401-410. 1964.-Representative strains of Bacteroides ruminicola were found to utilize peptide nitrogen or ammonia nitrogen, but not to utilize significant amounts of free amino acid nitrogen or the nitrogen from a variety of other low molecular weight compounds for growth. All strains grew well in a defined medium containing glucose, minerals, B-vitamins, heme, volatile fatty acids, methionine, and cysteine, with ammonia as the main nitrogen source. Methionine and cysteine were required by some strains. The only compounds found to replace ammonia as the main nitrogen source were a few proteins; tryptic digests of protein; peptide-rich fractions of Sephadex G-25 fractionated tryptic digests of casein; and the octapeptides, oxytocin and vasopressin. Most of the nitrogen present in these compounds was utilized. However, the organism did not utilize nitrogen from any of 12 dipeptides, triglycylglycine, glutathione, or mixtures of free amino acids. Possible reasons for the inability of B. ruminicola to utilize low molecular weight nitrogen compounds are discussed.

Amino Acids↗

PubMed2002

[Effect of free-air CO2 enrichment (FACE) on nitrogen accumulation and utilization efficiency in rice (Oryza sativa)].

Effect of FACE, 200 mumol.mol-1 CO2 elevation under field condition in this study, on nitrogen accumulation and nitrogen use efficiency in rice was investigated. Results showed that nitrogen content (%) in rice plant sampled at different growth stages decreased significantly under FACE treatment, but FACE had no obvious effect on nitrogen accumulation in rice plant due to the significant enhancement in dry matter production. FACE treatment resulted in the significant increase in nitrogen use efficiency for biomass production (NUEp) which was measured at 28th day after transplanting, at heading and at maturity, respectively. Significant increase in nitrogen use efficiency for grain output (NUEg) and nitrogen harvest index (NHI) under FACE treatment was also observed in this study. Nitrogen content (%) and nitrogen accumulation in rice plant were increased under high N, but nitrogen use efficiency in rice plant were decreased.

Air↗

PubMed2026

Mikania micrantha invasion restructures rhizosphere nitrogen cycling through enzyme activation, microbial recruitment, and allelopathic regulation.

BACKGROUND: Plant invasions profoundly influence terrestrial ecosystems by reshaping nutrient cycling processes. However, the mechanisms through which invasive plants such as Mikania micrantha modulate soil nitrogen (N) cycling and microbial communities remain insufficiently explored. Moreover, comparative studies with indigenous congener are scarce, limiting insights into whether such effects reflect species-specific strategies or genus-wide traits. This study investigates how M. micrantha modulates nitrogen metabolic pathways and rhizosphere microecology using combined metagenomic and metabolomic analyses. RESULTS: Integrated analyses revealed that M. micrantha established a distinctive "high total nitrogen-low mineral nitrogen" profile in the rhizosphere soil. Metagenomic profiling showed consistent enrichment of key ammonium assimilation enzymes, including glutamine synthetase and glutamate dehydrogenase, promoting enhanced incorporation of NH₄⁺ into organic nitrogen pools. In contrast, genes encoding nitrate reductase and nitrate transporters were significantly lower in relative abundance, limiting nitrate assimilation. Mikania micrantha also selectively enriched nitrogen-fixing microbes (notably rhizobia genera) and plant growth-promoting rhizobacteria (PGPR), thereby enhancing biological nitrogen fixation capacity. Metabolomic analysis further identified several allelopathic compounds in invaded soils at higher relative abundance, particularly epicatechin, which exhibited inhibitory effects on nitrifying bacteria. Compared with the congener Mikania cordata, which exerted weaker impacts on soil nitrogen cycling and microbial assembly, M. micrantha deployed a more comprehensive strategy integrating biochemical, microbial, and metabolic regulation. CONCLUSIONS: These findings demonstrate that under greenhouse-controlled conditions, M. micrantha reconfigures rhizosphere nitrogen cycling through a multi-dimensional strategy that couples biochemical regulation, microbial recruitment, and metabolite-mediated interference, thereby suggesting a potential mechanism that may contribute to its ecological advantage in natural settings. Video Abstract.

Rhizosphere↗

PubMed1998

Effects of systemic prostaglandin E1 on hepatic amino acid-nitrogen metabolism in patients with cirrhosis.

Prostaglandins of the E (PGE) series have long been considered "catabolic" hormones, but recent data suggest that they may be secreted in critically ill patients to counteract stress hormones, stimulating protein synthesis. Their use is under scrutiny to improve hepatic microcirculation and as cytoprotective agents. We tested the effects of PGE1 on hepatic and whole-body nitrogen metabolism in eight patients with cirrhosis. Urea-nitrogen synthesis rate, alpha-amino-nitrogen levels, and nitrogen exchange were measured in the basal, postabsorptive state and in response to continuous alanine infusion, in paired experiments, during superinfusion of PGE1 or saline. Splanchnic and systemic hemodynamics were assessed by echo-Doppler at the beginning and at the end of each experiment. PGE1 produced a rapid fall in plasma amino acids and in urea-nitrogen synthesis rate, as well as a positive nitrogen exchange. The slope of the regression of alpha-amino-nitrogen levels on urea-nitrogen synthesis rate, a measure of liver cell metabolic activity, was not affected, but the regression line was shifted rightward, suggesting a nitrogen-sparing effect of PGE1. Mesenteric artery and portal flow were unchanged, whereas femoral artery flow increased by 30%. Insulin and glucagon levels were not systematically different. We conclude that PGE1 reduces hepatic urea synthesis rate, independent of hormones and/or hepatic flow, possibly acting at the peripheral level on amino acid transport, thus reducing amino acid supply to the liver. The resulting net nitrogen sparing might be the basis for the beneficial effect of PGE1 in clinical hepatology.

Aged↗

PubMed2004

Nitrogen fixation and metabolism by groundwater-dependent perennial plants in a hyperarid desert.

The Central Asian Taklamakan desert is characterized by a hyperarid climate with less than 50 mm annual precipitation but a permanent shallow groundwater table. The perched groundwater (2-16 m) could present a reliable and constant source of nitrogen throughout the growing season and help overcome temporal nitrogen limitations that are common in arid environments. We investigated the importance of groundwater and nitrogen fixation in the nitrogen metabolism of desert plants by assessing the possible forms and availability of soil N and atmospheric N and the seasonal variation in concentration as well as isotopic composition of plant N. Water availability was experimentally modified in the desert foreland through simulated flooding to estimate the contribution of surface water and temporally increased soil moisture for nutrient uptake and plant-water relations. The natural vegetation of the Taklamakan desert is dominated by plants with high foliar nitrogen concentrations (2-3% DM) and leaf nitrate reductase activity (NRA) (0.2-1 micromol NO2- g(-1) FW h(-1)). There is little evidence that nitrogen is a limiting resource as all perennial plants exhibited fast rates of growth. The extremely dry soil conditions preclude all but minor contributions of soil N to total plant N so that groundwater is suggested as the dominant source of N with concentrations of 100 microM NO3-. Flood irrigation had little beneficial effect on nitrogen metabolism and growth, further confirming the dependence on groundwater. Nitrogen fixation was determined by the 15N natural abundance method and was a significant component of the N-requirement of the legume Alhagi, the average contribution of biologically fixed nitrogen in Alhagi was 54.8%. But nitrogen fixing plants had little ecological advantage owing to the more or less constant supply of N available from groundwater. From our data we conclude that the perennial species investigated have adapted to the environmental conditions through development of root systems that access groundwater to satisfy demands for both water and nutrients. This is an ecologically favourable strategy since only groundwater is a predictable and stable resource.

Atmosphere↗

PubMed2000

Atmospheric nitrogen in the Mississippi River Basin--emissions, deposition and transport.

Atmospheric deposition of nitrogen has been cited as a major factor in the nitrogen saturation of forests in the north-eastern United States and as a contributor to the eutrophication of coastal waters, including the Gulf of Mexico near the mouth of the Mississippi River. Sources of nitrogen emissions and the resulting spatial patterns of nitrogen deposition within the Mississippi River Basin, however, have not been fully documented. An assessment of atmospheric nitrogen in the Mississippi River Basin was therefore conducted in 1998-1999 to: (1) evaluate the forms in which nitrogen is deposited from the atmosphere; (2) quantify the spatial distribution of atmospheric nitrogen deposition throughout the basin; and (3) relate locations of emission sources to spatial deposition patterns to evaluate atmospheric transport. Deposition data collected through the NADP/NTN (National Atmospheric Deposition Program/National Trends Network) and CASTNet (Clean Air Status and Trends Network) were used for this analysis. NOx Tier 1 emission data by county was obtained for 1992 from the US Environmental Protection Agency (Emissions Trends Viewer CD, 1985-1995, version 1.0, September 1996) and NH3 emissions data was derived from the 1992 Census of Agriculture (US Department of Commerce. Census of Agriculture, US Summary and County Level Data, US Department of Commerce, Bureau of the Census. Geographic Area series, 1995:1b) or the National Agricultural Statistics Service (US Department of Agriculture. National Agricultural Statistics Service Historical Data. Accessed 7/98 at URL, 1998. http://www.usda.gov/nass/pubs/hisdata++ +.htm). The highest rates of wet deposition of NO3- were in the north-eastern part of the basin, downwind of electric utility plants and urban areas, whereas the highest rates of wet deposition of NH4+ were in Iowa, near the center of intensive agricultural activities in the Midwest. The lowest rates of atmospheric nitrogen deposition were on the western (windward) side of the basin, which suggests that most of the nitrogen deposited within the basin is derived from internal sources. Atmospheric transport eastward across the basin boundary is greater for NO3- than NH4+, but a significant amount of NH4+ is likely to be transported out of the basin through the formation of (NH4)2SO4 and NH4NO3 particles--a process that greatly increases the atmospheric residence time of NH4+. This process is also a likely factor in the atmospheric transport of nitrogen from the Midwest to upland forest regions in the North-East, such as the western Adirondack region of New York, where NH4+ constitutes 38% of the total wet deposition of N.

Air Pollutants↗

PubMed1997

Growth hormone prevents prednisolone-induced increase in functional hepatic nitrogen clearance in normal man.

BACKGROUND/AIMS: Glucocorticoid treatment increases urea excretion and leads to negative nitrogen balance. This effect is presumed mainly to reflect actions on tissue protein metabolism, but has been shown in rats to involve an hepatic element in the form of upregulation of the kinetics of ureagenesis. Likewise, the anabolic action of growth hormone administration has been shown to involve an hepatic element, just as growth hormone administration has been shown to prevent the protein catabolic side effects of prednisolone. Whether glucocorticoids increase the ability of the liver to convert amino-N to urea-N in man, and whether growth hormone counteracts any possible effect of glucocorticoid has not been studied. METHODS: We measured urea nitrogen synthesis rates and blood alpha-amino-N levels before, during, and after a 4-h constant i.v. infusion of alanine (2 mmol x kg BW(-1) x h(-1)). The urea nitrogen synthesis rate was estimated hourly as urinary excretion corrected for gut hydrolysis and accumulation in body water. The slope of the linear relationship between urea nitrogen synthesis rate and amino-N concentration represents the hepatic kinetics of conversion of amino- to urea-N, and is denoted the functional hepatic nitrogen clearance. Eight normal male subjects (aged 22-28 years; BMI 21.6-26.3 kg/m2) were randomly studied four times: i) after 4 days of s.c. saline injections, ii) after 4 days of s.c. growth hormone injections (0.1 IU x kg(-1) x day(-1)), iii) after 4 days of glucocorticoid administration (50 mg/d) and iv) after 4 days of growth hormone and glucocorticoid administration. All injections were given at 20 00 hours and 25 mg prednisolone was given morning and evening. RESULTS: Growth hormone decreased functional hepatic nitrogen clearance (l/h) by 21% (from 38.8+/-1.8 l/h (control) to 30.5+/-2.7 l/h (4 d growth hormone) (mean+/-SE) (ANOVA; p<0.05)). Glucocorticoid increased functional hepatic nitrogen clearance by 23% (47.7+/-3.3 l/h, p<0.05), while growth hormone plus glucocorticoid offset any effect on functional hepatic nitrogen clearance (36.2+/-3.3 l/h, p=0.83). CONCLUSIONS: Glucocorticoid administration leads to loss of nitrogen as urea, in part due to a specific hepatic mechanism, as shown by the increased functional hepatic nitrogen clearance. Growth hormone has the opposite effect, and also neutralises the glucocorticoid effect when given together with prednisolone. This adds to the understanding of the development and treatment possibilities of steroid catabolism.

Adult↗

PubMed1997

Nitrogen levels in long bones from coffin burials interred for periods of 26-90 years.

Samples of long bones were obtained from 42 bodies buried in coffins at two sites over a 26 to 93 year period. Quicklime had been added to 17 of the coffins and there was fuel oil contamination of three of these. Long bone total nitrogen levels obtained by the macro Kjeldahl method were subjected to statistical analysis and their distribution plotted on a graph of burial time versus bone total nitrogen content. The highest nitrogen level recorded was 4.06 g per 100 g of bone (26 years) and the lowest 3.27 g per 100 g of bone (80 years). The oldest burial (93 years) gave a total nitrogen level of 3.49 g per 100 g of bone. For practical purposes, for burials deeper than 4 ft, the rate at which nitrogen is lost is independent of depth of burial. Although the overall trend was for nitrogen content to decrease with age, it was noted that despite being the oldest of the burials, the quicklime burials still possessed a relatively high nitrogen content. The maintenance of a relatively high nitrogen content in the quicklime burials was thought at first to be due to the quicklime acting as an inhibitor of decomposition during the initial period of interment. Statistical analysis, however, showed there to be no correlation between the addition of lime and the bone nitrogen level. Fuel oil contamination of three of the skeletons led to a high nitrogen content being recorded in the long bones, giving the impression that those burials were more recent than they actually were.

Adult↗

PubMed1999

Regulation of nitrogen metabolism in Bacillus subtilis: vive la différence!

Nitrogen metabolism genes of Bacillus subtilis are regulated by the availability of rapidly metabolizable nitrogen sources, but not by any mechanism analogous to the two-component Ntr regulatory system found in enteric bacteria. Instead, at least three regulatory proteins independently control the expression of gene products involved in nitrogen metabolism in response to nutrient availability. Genes expressed at high levels during nitrogen-limited growth are controlled by two related proteins, GlnR and TnrA, which bind to similar DNA sequences under different nutritional conditions. The TnrA protein is active only during nitrogen limitation, whereas GlnR-dependent repression occurs in cells growing with excess nitrogen. Although the nitrogen signal regulating the activity of the GlnR and TnrA proteins is not known, the wild-type glutamine synthetase protein is required for the transduction of this signal to the GlnR and TnrA proteins. Examination of GlnR- and TnrA-regulated gene expression suggests that these proteins allow the cell to adapt to growth during nitrogen-limited conditions. A third regulatory protein, CodY, controls the expression of several genes involved in nitrogen metabolism, competence and acetate metabolism in response to growth rate. The highest levels of CodY-dependent repression occur in cells growing rapidly in a medium rich in amino acids, and this regulation is relieved during the transition to nutrient-limited growth. While the synthesis of amino acid degradative enzymes in B. subtilis is substrate inducible, their expression is generally not regulated in response to nitrogen availability by GlnR and TnrA. This pattern of regulation may reflect the fact that the catabolism of amino acids produced by proteolysis during sporulation and germination provides the cell with substrates for energy production and macromolecular synthesis. As a result, expression of amino acid degradative enzymes may be regulated to ensure that high levels of these enzymes are present in sporulating cells and in dormant spores.

Bacillus subtilis↗