Showing papers on "Urea published in 2000"
TL;DR: Solubilized r-hGH in Tris buffer containing 2 M urea was found to be less susceptible to aggregation during buffer exchange and thus was refolded by simple dilution, improving the yield of bioactive protein during refolding.
244 citations
TL;DR: Dynamic analysis of models demonstrated that enhancing initial nitrogen concentration in fermentor cultures, which correspondingly enhances cell growth and lutein formation, may shorten the fermentation cycle by 25-46%.
236 citations
TL;DR: In this paper, the solubility analysis, viscometry and light scattering of cellulose in 6-8 wt% NaOH/urea aqueous solutions were performed by using Bemliese® solvent.
Abstract: NaOH/urea aqueous solution as solvent of cellulose including cotton linter, bagasse, alkali-soluble cellulose and Bemliese® was studied by solubility analysis, viscometry and light scattering. The addition of 2—4 wt% urea significantly improved the solubility of cellulose in 6—8 wt% NaOH aqueous solutions, and moderate urea plays a role in improving solubility and avoiding the formation of cellulose gel. Celluloses I with viscosity-average molecular weight (Mη) of 6.7×104 were completely dissolved in 6 wt% NaOH/4 wt% urea aqueous solution. Cellulose dissolved in 6 wt% NaOH/4 wt% urea aqueous solution degraded slowly with storage time, and Mη of cellulose in the solution decreased 20% after storage for 100 days. The stability of cellulose solution was higher than cellulose cuoxam. A regenerated cellulose membrane having the tensile strength of 88.7MPa and breaking elongation of 11% was successfully prepared by coagulating 4 wt% Bemliese® solution in 6 wt% NaOH/4 wt% urea with 5 wt% CaCl2 then 1.3 wt% HCl aqueous solution as coagulate at 20°C.
229 citations
TL;DR: In this article, a model of a V2O5-MoO3-TiO2 DeNOx catalyst has been presented and briefly characterized, and the adsorption of urea on it has also been investigated.
Abstract: A model V2O5–MoO3–TiO2 DeNOx catalyst has been prepared and briefly characterized. The adsorption of urea on it (and of ammonia for comparison) has also been investigated. It has been observed that urea can adsorb over the catalyst in an anionic form that can later decompose to isocyanate anions and ammonia and ammonium ion species. This mechanism suggests that the potential reactivity of the anionic form of urea and of isocyanate anions with VOCs, if they are present in the waste gas, possibly rise to polluting compounds must be taken into account for applications of the urea/DeNOx process.
213 citations
TL;DR: Elevated NaCl and/or urea reduces the number of proliferating mIMCD3 cells by slowing the transit through the S phase, by cell cycle delay in the G(2)M and G(1), and by inducing apoptotic cell death.
Abstract: We investigated the effects of hyperosmolality on survival and proliferation of subconfluent cultures of mIMCD3 mouse renal collecting duct cells. High NaCl and/or urea (but not glycerol) reduces t...
211 citations
TL;DR: This review describes the quantitative aspects of urea and ammonia metabolism in ruminants and it relates the metabolic or economic costs of that metabolism to practical feeding situations and concludes with a discussion of conflicts and considerations among three main priorities in rulerant N metabolism.
Abstract: Nitrogen was recognized over 200 yr ago as an element essential for normal function of farm animals. During the first half of the 19th century, the roles of proteins and urea in N metabolism were discovered. By the middle of the 20th century, the substrates, products, and enzymes of the urea cycle were elucidated. Work since then has quantified dietary crude protein requirements for specific production goals, protein synthesis and breakdown, ruminal ammonia production, endogenous urea synthesis, and urea recycling. In ruminants fed conventional diets, N absorbed as ammonia can be several times the amount of N absorbed in the form of amino acids or peptides. Nitrogen recycled to the digestive tract as urea in saliva or urea transported from blood ranges from 10 to 40% of N consumed in feed. Under production conditions, from 0 to 20% of N consumed by ruminants is retained as tissue N or excreted as milk protein. This review describes the quantitative aspects of urea and ammonia metabolism in ruminants and it relates the metabolic or economic costs of that metabolism to practical feeding situations. The review concludes with a discussion of conflicts and considerations among three main priorities in ruminant N metabolism: 1) maximizing microbial function in the rumen; 2) optimizing amino acid supply to the host ruminant; and 3) minimizing negative environmental effects of cycling N through ruminant production systems.
200 citations
TL;DR: Results indicate that soy proteins modified with urea and GH enhance water resistance as well as adhesive strength and may have higher content of secondary structure and more exposed hydrophobic amino acids compared with other modifications or unmodified proteins.
Abstract: An investigation was conducted on the adhesive and water-resistance properties of soy protein isolates that were modified by varying solutions of urea (1, 3, 5, and 8 M) or guanidine hydrochloride (GH) (0.5, 1, and 3 M) and applied on walnut, cherry, and pine plywoods. Soy proteins modified by 1 and 3 M urea showed greater shear strengths than did unmodified protein. The 3 M urea modification gave soy protein the highest shear strength. Soy proteins modified with 0.5 and 1 M GH gave greater shear strengths than did the unmodified protein. The 1 M GH-modified soy protein gave the highest shear strength. Compared to the unmodified protein, the modified proteins also exhibited higher shear strengths after incubating with two cycles of alternating relative humidity, zero delamination, and higher remaining shear strengths after three cycles water soaking and drying. These results indicate that soy proteins modified with urea and GH enhance water resistance as well as adhesive strength. Secondary structures of globule proteins may enhance adhesion strength, and the exposure of hydrophobic amino acids may enhance water resistance. Proteins modified by 3 M urea or 1 M GH may have higher content of secondary structure and more exposed hydrophobic amino acids, compared with other modifications or unmodified proteins.
176 citations
TL;DR: In this article, the uptake of ammonium, nitrate, amino acids and urea was examined in the nitrate-rich Thames estuary and adjacent area in the North Sea during February 1999.
Abstract: The uptake of ammonium, nitrate, amino acids and urea was examined in the nitrate- rich Thames estuary and adjacent area in the North Sea during February 1999. The majority of uptake was by heterotrophic bacteria, as demonstrated by addition of a prokaryotic inhibitor that lowered uptake rates by 82, 66, 49 and 86% for ammonium, nitrate, amino acids and urea, respec- tively. Amino acids were preferred over ammonium and urea, which in turn were preferred over nitrate. Urea was not important as nitrogen substrate. Amino acids were the main nitrogen substrate offshore and at the mouth of the estuary, but in the inner estuary nitrogen was mainly taken up as ammonium and, even more, as nitrate. Nitrate appeared to be the main substrate in the inner estuary (60 to 90%) despite its low affinity for nitrate. The high nitrate uptake by heterotrophic bacteria is probably due to high ambient concentrations of nitrate (up to 650 µM).
174 citations
TL;DR: In this paper, the thermal denaturation of α-lactalbumin (α-lac), β -lactoglobulin (β-lg) and a mixture of the two proteins in the presence of several sugars, sodium salts and at various pH values was studied by differential scanning calorimetry.
149 citations
TL;DR: In this article, a hydroxide-bridged dinuclear nickel complex with a urea molecule linking the two metal ions through its carbonyl oxygen atom has been prepared as a model for the metalloenzyme urease.
Abstract: A hydroxide-bridged dinuclear nickel complex with a urea molecule linking the two metal ions through its carbonyl oxygen atom has been prepared as a model for the metalloenzyme urease. This complex, [Ni2(μ-OH)(μ-urea)(bdptz)(urea)(CH3CN)](ClO4)3, where bdptz is the dinucleating ligand 1,4-bis(2,2‘-dipyridylmethyl)phthalazine, effects the hydrolysis of urea upon heating in a two-step reaction. In the first step, a molecule of ammonia is eliminated from urea with concomitant production of cyanate, the first-order rate constant in acetonitrile being (7.7 ± 0.5) × 10-4 h-1. This reaction is at least 500 times faster than the spontaneous decomposition of urea under the same conditions. When the cyanate-containing product is further heated in the presence of water, the cyanate is hydrolyzed with a second-order rate constant of (9.5 ± 1) × 10-4 M-1 h-1. Reaction of [Ni2(μ-OH)(μ-urea)(bdptz)(urea)(CH3CN)](ClO4)3 in 50% aqueous acetonitrile afforded ammonia with no appreciable buildup of the cyanate-containing spe...
146 citations
TL;DR: One-dimensional hydrogen-bonding aggregates of urea and thiourea corresponding to the two patterns, chains and ribbons, which are found in crystal structures of these molecules have been studied us as mentioned in this paper.
Abstract: One-dimensional hydrogen-bonding aggregates of urea and thiourea corresponding to the two patterns, chains and ribbons, which are found in crystal structures of these molecules have been studied us...
TL;DR: The urea breath test is the noninvasive method of choice to determine Helicobacter pylori status as mentioned in this paper, based on the organism's urease activity, which liberates carbon dioxide (CO 2 ) from urea and produces ammonia to buffer its acidic environment.
TL;DR: A comparison of the effects of various potassium salts revealed that anions were chiefly responsible in stabilizing HSA, suggesting that preferential binding of anions to HSA rather than hydration, was primarily responsible for stabilization.
Abstract: The unfolding of human serum albumin (HSA), a multidomain protein, by urea was followed by far-UV circular dichroism (CD), intrinsic fluorescence, and ANS fluorescence measurements. The urea-induced transition, which otherwise was a two-step process with a stable intermediate at around 4.8 M urea concentration as monitored by far-UV CD and intrinsic fluorescence, underwent a single-step cooperative transition in the presence of 1.0 M KCl. The free energy of stabilization (DeltaDelta G(H2O)D) in the presence of 1 M KCl was found to be 1,090 and 1,200 cal/mol as determined by CD and fluorescence, respectively. The salt stabilization occurred in the first transition (0-5.0 M urea), which corresponded to the formation of intermediate (I) state from the native (N) state, whereas the second transition, corresponding to the unfolding of I state to denatured (D) state, remained unaffected. Urea denaturation of HSA as monitored by tryptophan fluorescence of the lone tryptophan residue (Trp(214)) residing in domain II of the protein, followed a single-step transition suggesting that domain(s) I and/or III is (are) involved in the intermediate formation. This was also confirmed by the acrylamide quenching of tryptophan fluorescence at 5 M urea, which exhibited little change in the value of Stern-Volmer constant. ANS fluorescence data also showed single-step transition reflecting the absence of accumulation of hydrophobic patches. The stabilizing potential of various salts studied by far-UV CD and intrinsic fluorescence was found to follow the order: NaClO(4) > NaSCN >Na(2)SO(4) >KBr >KCl >KF. A comparison of the effects of various potassium salts revealed that anions were chiefly responsible in stabilizing HSA. The above series was found similar to the electroselectivity series of anions towards the anion-exchange resins and reverse of the Hofmeister series, suggesting that preferential binding of anions to HSA rather than hydration, was primarily responsible for stabilization. Further, single-step transition observed with GdnHCl can be ascribed to its ionic character as the free energy change associated with urea denaturation in the presence of 1.0 M KCl (5,980 cal/mol) was similar to that obtained with GdnHCl (5,870 cal/mol).
TL;DR: In this article, the synthesis of macrocyclic and acyclic cleft-like anion receptors in which four hydrogen bond donating urea moieties are present in a preorganized fashion is described.
TL;DR: The effect of diet quality on urea production, entry into the gastrointestinal tract (GIT) and subsequent diversion to anabolic or catabolic fates was examined in four sheep.
Abstract: The effect of diet quality on urea production, entry into the gastrointestinal tract (GIT) and subsequent diversion to anabolic or catabolic fates was examined in four sheep (mean live weight 49.5 kg). The animals received, in a crossover design, each of two rations, hay-grass pellets (1:1 HG) and a mixed concentrate-forage (CF). Measurements were made of N balance and urea kinetics based on a 4 d continuous intravascular infusion of [ 15 N 15 N]urea. Enrichments of [ 15 N 15 N]- and [ 14 N 15 N]urea in the urine, and faecal 15 N content were determined each day. After 24 h of infusion, urinary [ 15 N 15 N]urea enrichments reached constant enrichment but a further 24 h was required before [ 14 N 15 N]urea enrichment was at plateau. The latter is derived from hydrolysis of urea to 15 NH 3 in the digestive tract with subsequent absorption and reconversion to urea. The diets were not isonitrogenous (14.3 v. 17.1 g N supplied daily for HG and CF respectively) but showed no difference in N balance. Urea-N production was much greater (16.3 v. 11.1 g/d; P = 0.011) for CF compared with HG and more urea-N entered the GIT (9.9 ν. 7.7; P = 0.07). A larger proportion of GIT entry was returned to ureagenesis (51 ν. 42 %; P = 0.047) for the CF diet but a smaller fraction was lost in the faeces (3.3 % ν. 7.1 %; P = 0.013). In consequence, most of the additional urea-N which entered the GIT on the CF diet was returned to the ornithine cycle (probably as NH 3 ) and the absolute amount available for anabolic purposes was similar between the rations (3.9 v. 4.5 g N/d).
TL;DR: In this paper, a field experiment was conducted to evaluate chemically synthesized as well as locally available neem plant products on N2O emissions, from an irrigated rice at New Delhi, India.
TL;DR: Results suggest that H. pylori-associated urease functions to produce a potent ONOO− scavenger, CO2/HCO3−, that defends the bacteria from OnOO− cytotoxicity, and may facilitate sustained bacterial colonization in the infected gastric mucosa.
Abstract: Helicobacter pylori can produce a persistent infection in the human stomach, where chronic and active inflammation, including the infiltration of phagocytes such as neutrophils and monocytes, is induced. H. pylori may have a defense system against the antimicrobial actions of phagocytes. We studied the defense mechanism of H. pylori against host-derived peroxynitrite (ONOO(-)), a bactericidal metabolite of nitric oxide, focusing on the role of H. pylori urease, which produces CO(2) and NH(3) from urea and is known to be an essential factor for colonization. The viability of H. pylori decreased in a time-dependent manner with continuous exposure to 1 microM ONOO(-), i.e., 0.2% of the initial bacteria remained after a 5-min treatment without urea. The bactericidal action of ONOO(-) against H. pylori was significantly attenuated by the addition of 10 mM urea, the substrate for urease, whereas ONOO(-)-induced killing of a urease-deficient mutant of H. pylori or Campylobacter jejuni, another microaerophilic bacterium lacking urease, was not affected by the addition of urea. Such a protective effect of urea was potentiated by supplementation with exogenous urease, and it was almost completely nullified by 10 microM flurofamide, a specific inhibitor of urease. The bactericidal action of ONOO(-) was also suppressed by the addition of 20 mM NaHCO(3) but not by the addition of 20 mM NH(3). In addition, the nitration of L-tyrosine of H. pylori after treatment with ONOO(-) was significantly reduced by the addition of urea or NaHCO(3), as assessed by high-performance liquid chromatography with electrochemical detection. These results suggest that H. pylori-associated urease functions to produce a potent ONOO(-) scavenger, CO(2)/HCO(3)(-), that defends the bacteria from ONOO(-) cytotoxicity. The protective effect of urease may thus facilitate sustained bacterial colonization in the infected gastric mucosa.
TL;DR: Membrane-immobilized urease could be utilized in a two-compartment membrane reactor with temperature swing to substantially enhance urea hydrolysis rate and shows enhanced thermal stability after immobilization.
TL;DR: In this paper, a conductometric urea biosensor based on sol-gel-immobilized urease on a screen-printed inter-digitated array (IDA) electrode has been developed.
TL;DR: In this paper, N,N′-di(2-ethylhexyl)urea was shown by viscosimetry and FTIR spectroscopy to be associated in heptane at concentrations higher than 10 g l−1.
Abstract: N,N′-Dialkylureas, which form intermolecular hydrogen bonds, are
interesting precursors in the field of supramolecular chemistry.
Particularly, N,N′-di(2-ethylhexyl)urea, which is soluble in
nonpolar solvents, was shown by viscosimetry and FTIR spectroscopy to be associated in heptane at concentrations higher
than 10 g l−1. The interactions involved are strongly reinforced by the cooperative association of two urea groups in the case of bis-ureas
prepared from 2,4-toluene diisocyanate.
TL;DR: It is suggested that at low temperatures two kinds of hydrogen bonds are formed by urea molecules in urea-intercalated kaolinite.
TL;DR: Hepatic triglyceride accumulation may inhibit ureagenesis and result in increased circulating ammonia, Gln% and urinary ammonia N in vivo, and hepatocytes where Gln synthesis occurs and increasing ammonia concentration in blood leaving the liver.
TL;DR: Results from four separate experiments in healthy young adults carried out in laboratories and all at the end of the respective diet periods support the generally accepted view that a control of body N balance is via a regulation of urea production, but do not support the concept that urea hydrolysis is the more important site in the control ofBody N loss.
Abstract: The quantitative relationships between nitrogen (N) intake, urea production, excretion and amino acid oxidation are currently a matter of debate. Some investigators have proposed that urea production is essentially constant over a wide range of N intakes and that urea hydrolysis is regulated according to the N needs of the organism. We have assessed this proposal by compiling results from four separate experiments in healthy young adults (n = 34) carried out in our laboratories and all at the end of the respective diet periods using an identical 24-h continuous intravenous infusion of [(15)N, (15)N]urea and L-[1-(13)C]leucine. The N intakes were: expt. 1; protein-free diet for 5 d; expt. 2; N at 44 mg N. kg(-1). d(-1) from a balanced L-amino acid mixture for 13 d; expt. 3; N at 161 mg. kg(-1). d(-1) from egg protein for 6 d; expt. 4 -one group received 157 mg. kg(-1). d(-1) and the other 392 mg. kg(-1). d(-1) from milk-protein-based diets for 6 d. Urea production and excretion were linearly correlated with N intake (r = 0.98 and 0.94, respectively; P < 0.01). Urea hydrolysis increased linearly with N intake (r = 0.7; P < 0.05), with considerable variation in the rate among individuals, especially at the N intake of approximately 160 mg N. kg(-1)d(-1). These findings are consistent with the generally accepted view that a control of body N balance is via a regulation of urea production. They do not support the concept that urea hydrolysis is the more important site in the control of body N loss.
TL;DR: In this article, the authors measured the spin-lattice relaxation times (T1) of the 17O nucleus of a water molecule in guanidine hydrochloride, urea, and alkylated ureas at 25 °C.
TL;DR: Through retarding ammonia release from urea and increasing the proportion of propionate in ruminal VFA, Zn supplementation at a concentration of 250 ppm may decrease the likelihood of urea toxicity and increase energetic efficiency of ruminal fermentation.
Abstract: One in vitro and one in vivo metabolism experiment were conducted to examine the effects of supplemental Zn on ruminal parameters, digestion, and DMI by heifers fed low-quality prairie hay supplemented with urea. In Exp. 1, prairie hay was incubated in vitro for 24 h with five different concentrations of supplemental Zn (0, 5, 10, 15, and 20 ppm) and two concentrations of supplemental Mn (0 and 100 ppm), both provided as chloride salts. Added Mn increased (P < 0.02) IVDMD, but added Zn linearly decreased (P < 0.03) IVDMD. Added Zn tended to increase the amount of residual urea linearly (P < 0.06) at 120 min and quadratically (P < 0.02) at 180 min of incubation, although added Mn counteracted these effects of added Zn. Six 363-kg heifers in two simultaneous 3 x 3 Latin squares were fed prairie hay and dosed once daily via ruminal cannulas with urea (45 or 90 g/d) and with Zn chloride to provide the equivalent of an additional 30 (the dietary requirement), 250, or 470 ppm of dietary Zn. After a 7-d adaptation period, ruminal contents were sampled 2, 4, 6, 12, 18, 21, and 24 h after the supplement was dosed. Supplemental Zn did not alter prairie hay DMI (mean = 4.9 kg/d) or digestibility, although 470 ppm added Zn tended to decrease (P < 0.06) intake of digestible DM, primarily due to a trend for reduced digestibility with 470 ppm supplemental Zn. Zinc x time interactions were detected for both pH (P = 0.06) and NH3 (P = 0.06). At 2 h after dosing, ruminal pH and ruminal ammonia were linearly decreased (P < 0.05; P < 0.01) by added Zn. At 5 h after feeding, ruminal pH was linearly increased (P < 0.05) by added Zn, suggesting that added Zn delayed ammonia release from urea. The molar proportion of propionate in ruminal fluid was linearly and quadratically increased (P < 0.02; P < 0.01) whereas the acetate:propionate ratio was linearly and quadratically decreased (P = 0.02; P < 0.05) by added Zn. Through retarding ammonia release from urea and increasing the proportion of propionate in ruminal VFA, Zn supplementation at a concentration of 250 ppm may decrease the likelihood of urea toxicity and increase energetic efficiency of ruminal fermentation.
TL;DR: In this paper, the authors used differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and wide-angle X-ray diffraction (WAXD) to verify the formation and successfully characterize all inclusion compounds.
Abstract: α-Cyclodextrin (α-CD) and urea (U) hosts were used in order to separate a mixture of poly(ethylene glycols) (PEGs) with two different molecular weights (Mw = 600 [PEG600] and Mw = 20 000 [PEG20000]) by forming the respective inclusion compounds (ICs). Differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and wide-angle X-ray diffraction (WAXD) have been used to verify the formation and successfully characterize all inclusion compounds. The high melting point of the urea inclusion compound (PEG*-U IC) formed from the solution containing both polymers was the first evidence that urea preferentially included poly(ethylene glycol) with the higher molecular weight. The PEG*-U IC and PEG20000-U IC X-ray diffraction patterns and FTIR spectra were very similar to each other, confirming that urea preferentially complexes PEG20000 in their mutual solution. Since the above-mentioned techniques were not as useful in the case of α-CD ICs, viscosity measurements were made in order to ...
TL;DR: In this article, a review focused on the gastric acid pump as a therapeutic target for the control of acid secretion in peptic ulcer and gastro-oesophageal reflux disease.
Abstract: This review focuses on the gastric acid pump as a therapeutic target for the control of acid secretion in peptic ulcer and gastro-oesophageal reflux disease. The mechanism of the proton pump inhibitors is discussed as well as their clinical use. The biology of Helicobacter pylori as a gastric denizen is then discussed, with special regard to its mechanisms of acid resistance. Here the properties of the products of the urease gene clusters, ureA, B and ureI, E, F, G and H are explored in order to explain the unique location of this pathogen. The dominant requirement for acid resistance is the presence of a proton gated urea transporter, UreI, which increases access of gastric juice urea to the intrabacterial urease 300-fold. This enables rapid and continuous buffering of the bacterial periplasm to approximately pH 6.0, allowing acid resistance and growth at acidic pH in the presence of 1 mM urea. A hypothesis for the basis of combination therapy for eradication is also presented.
TL;DR: The varying polymer structures of wood adhesive-type urea-formaldehyde resins resulting from different formaldehyde/first urea (F/U1) mole ratios used in the first step of resin manufacture were investigated using 13C as mentioned in this paper.
Abstract: The varying polymer structures of wood adhesive-type urea–formaldehyde resins resulting from different formaldehyde/first urea (F/U1) mole ratios used in the first step of resin manufacture were investigated using 13C. As the F/U1 mole ratio decreased progressively from 2.40 to 2.10 and to 1.80, the viscosity increase due to polymerization during resin synthesis became faster and resulted in decreasing side-chain branches and increasing free urea amide groups in the resin structure. The resultant UF resins, with the second urea added to an overall F/(U1 + U2) of 1.15, showed viscosity decreases when heated with stirring or allowed to stand at room temperature that were also characteristic with the F/U1 mole ratios used in resin synthesis. The formaldehyde emission levels of particleboards bonded with the freshly made UF resins showed relatively small but similarly characteristic variations. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2800–2814, 2001
TL;DR: The results of the decreased plasma concentrations of arginine and nitrate plus nitrite, as well as the increased plasma ammonia concentration, indicate a hitherto unrecognized deficiency of Arginine in 7- to 21-d-old suckling pigs.
Abstract: Amino acids, ammonia, urea, orotate, and nitrate plus nitrite (stable oxidation products of nitric oxide) were determined in plasma of 1- to 21-d-old suckling pigs. Jugular venous blood samples were obtained from pigs at 1, 3, 7, 14, and 21 d of age for analysis of plasma amino acids and metabolites by HPLC and enzymatic methods. Plasma concentrations of arginine and its immediate precursors (citrulline and ornithine) decreased (P 0.05) in plasma concentrations of other amino acids. Plasma concentrations of ammonia increased (P < 0.01) by 18 and 46%, whereas those of nitrate plus nitrite decreased (P < 0.01) by 16 and 29%, in 7- and 14-d-old pigs, respectively, compared with 1- to 3-d-old pigs. Because arginine plays a crucial role in ammonia detoxification via the hepatic urea cycle and is the physiological substrate for nitric oxide synthesis, our results of the decreased plasma concentrations of arginine and nitrate plus nitrite, as well as the increased plasma ammonia concentration, indicate a hitherto unrecognized deficiency of arginine in 7- to 21-d-old suckling pigs. Arginine is an essential amino acid for piglets and has a great potential to enhance neonatal growth; therefore, further studies are necessary to elucidate the mechanism responsible for arginine deficiency in sow-reared piglets and to identify hormonal and metabolic means for improving neonatal arginine nutrition and growth.