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PubMed2000

High hopanoid/total lipids ratio in Frankia mycelia is not related to the nitrogen status.

Vesicles are specific Frankia structures which are produced under nitrogen-limiting culture conditions. Hopanoids are the most abundant lipids in these vesicles and are believed to protect the nitrogenase against oxygen. The amounts and quality of each hopanoid were estimated in different Frankia strains cultivated under nitrogen-depleted and nitrogen-replete conditions in order to detect a possible variation. Studied Frankia strains nodulating Eleagnus were phylogenetically characterized by analysis of the nifD-K intergenic region as closely related to genomic species 4 and 5. Phylogenetically different strains belonging to three infectivity groups were cultivated in the same medium with and without nitrogen source for 10 d before hopanoid content analysis by HPLC. Four hopanoids together accounted for 23-87% and 15-87% of the total lipids under nitrogen-replete and nitrogen-depleted culture conditions, respectively. Two of the hopanoids found, bacteriohopanetetrols and their phenylacetic acid esters, have previously been described in Frankia Two new hopanoids, moretan-29-ol and a bacteriohopanetetrol propionate, have also been identified. The moretan-29-ol and bacteriohopanetetrols were found to be the most abundant hopanoids whereas the bacteriohopanetetrol propionate and phenylacetates were present at a concentration close to the limit of detection. The ratio of (bacteriohopanetetrols + moretan-29-ol)/(total lipids) varied in most of the strains between nitrogen-depleted and nitrogen-replete culture conditions. In most of the strains, the hopanoid content was found to be slightly higher under nitrogen-replete conditions than under nitrogen-depleted conditions. These results suggest that remobilization, rather than neosynthesis of hopanoids, is implicated in vesicle formation in Frankia under nitrogen-depleted conditions.

Actinomycetales↗
PubMed2001

Nitrogen deposition and leaching from two forested catchments in Southwest China--preliminary data and research needs.

Increased nitrogen deposition has resulted in increased nitrogen pools and nitrogen leaching in European and North American forest soils. The development in Asia in general, and China in particular, suggests increased deposition of reduced nitrogen from changes in agricultural practices and of oxidized nitrogen from rapid growth of the transportation sector. Decreased nitrogen retention in forested areas in the future may cause increased NO3- leaching and, thus, acidification and eutrophication in surface waters. The differences in climate, ecosystems, land use, and deposition history make direct application of knowledge from studies in Europe and North America difficult. In Southwest China the potential for nitrogen mobilization from forest soils may be high because of the warm and humid climate, resulting in high decomposition rates of soil organic matter. However, there are very few data available for quantifying the suspected potential for increased nitrogen leaching in forest ecosystems. Here we present data from two forested catchments, dominated by Masson pine (Pinus massoniana), near Guiyang and Chongqing, respectively, in Southwest China. The present nitrogen deposition is moderate, estimated in the range from 10 to 40 kg N ha(-1) year(-1). The C/N ratios of the soils are generally below 15. Nitrate concentrations in soil water are rather variable in space, with highest values of several hundred microequivalents per liter. The turnover rate of nitrogen in the forest ecosystem is quite high compared to the atmospheric deposition rate. At present, nitrate runoff from the catchments is low and intermediate in Guiyang and Chongqing, respectively. More research is needed to improve our ability to predict future nitrogen leaching from subtropical Asian coniferous forests.

Carbon↗
PubMed2000

The role of ammonia metabolism in nitrogen catabolite repression in Saccharomyces cerevisiae.

Saccharomyces cerevisiae is able to use a wide variety of nitrogen sources for growth. Not all nitrogen sources support growth equally well. In order to select the best out of a large diversity of available nitrogen sources, the yeast has developed molecular mechanisms. These mechanisms consist of a sensing mechanism and a regulatory mechanism which includes induction of needed systems, and repression of systems that are not beneficial. The first step in use of most nitrogen sources is its uptake via more or less specific permeases. Hence the first level of regulation is encountered at this level. The next step is the degradation of the nitrogen source to useful building blocks via the nitrogen metabolic pathways. These pathways can be divided into routes that lead to the degradation of the nitrogen source to ammonia and glutamate, and routes that lead to the synthesis of nitrogen containing compounds in which glutamate and glutamine are used as nitrogen donor. Glutamine is synthesized out of ammonia and glutamate. The expression of the specific degradation routes is also regulated depending on the availability of a particular nitrogen source. Ammonia plays a central role as intermediate between degradative and biosynthetic pathways. It not only functions as a metabolite in metabolic reactions but is also involved in regulation of metabolic pathways at several levels. This review describes the central role of ammonia in nitrogen metabolism. This role is illustrated at the level of enzyme activity, translation and transcription.

Ammonia↗
PubMed1999

Nitrogen availability to Pseudomonas fluorescens DF57 is limited during decomposition of barley straw in bulk soil and in the barley rhizosphere.

The availability of nitrogen to Pseudomonas fluorescens DF57 during straw degradation in bulk soil and in barley rhizosphere was studied by introducing a bioluminescent reporter strain (DF57-N3), responding to nitrogen limitation, to model systems of varying complexity. DF57-N3 was apparently not nitrogen limited in the natural and sterilized bulk soil used for these experiments. The soil was subsequently amended with barley straw, representing a plant residue with a high carbon-to-nitrogen ratio (between 60 and 100). In these systems the DF57-N3 population gradually developed a nitrogen limitation response during the first week of straw decomposition, but exclusively in the presence of the indigenous microbial population. This probably reflects the restricted ability of DF57 to degrade plant polymers by hydrolytic enzymes. The impact of the indigenous population on nitrogen availability to DF57-N3 was mimicked by the cellulolytic organism Trichoderma harzianum Rifai strain T3 when coinoculated with DF57-N3 in sterilized, straw-amended soil. Limitation occurred concomitantly with fungal cellulase production, pointing to the significance of hydrolytic activity for the mobilization of straw carbon sources, thereby increasing the nitrogen demand. Enhanced survival of DF57-N3 in natural soil after straw amendment further indicated that DF57 was cross-fed with carbon/energy sources. The natural barley rhizosphere was experienced by DF57-N3 as an environment with restricted nitrogen availability regardless of straw amendment. In the rhizosphere of plants grown in sterilized soil, nitrogen limitation was less severe, pointing to competition with indigenous microorganisms as an important determinant of the nitrogen status for DF57-N3 in this environment. Hence, these studies have demonstrated that nitrogen availability and gene expression in Pseudomonas is intimately linked to the structure and function of the microbial community. Further, it was demonstrated that the activities of cellulolytic microorganisms may affect the availability of energy and specific nutrients to a group of organisms deficient in hydrolytic enzyme activities.

Biodegradation, Environmental↗
PubMed2005

Nuclear accumulation of the GATA factor AreA in response to complete nitrogen starvation by regulation of nuclear export.

Both the availability and the quality of nutrients affect cellular functions by controlling gene activity. AreA, a member of the GATA family of transcription factors, globally activates expression of genes involved in nitrogen source utilization in Aspergillus nidulans. The quality of the nitrogen source determines the level and activation capacity of AreA through controls at the level of areA mRNA stability and by interaction of AreA with the corepressor NmrA. The availability of potential nitrogen sources also affects the activation capacity of AreA. We show that the complete absence of a nitrogen source results in an enhanced level of AreA-dependent gene expression and that this response is independent of mechanisms regulating AreA activity in response to nitrogen source quality. During nitrogen starvation AreA accumulates in the nucleus, but the presence of a potential nitrogen source or carbon starvation prevents this accumulation. Furthermore, accumulated AreA is rapidly lost from the nuclei of nitrogen-starved cells when a nitrogen source is supplied or when a carbon source is absent, and this accompanies arrest of the AreA-dependent nitrogen starvation response on regulated gene expression. By the generation of a leptomycin B-sensitive mutant, we have been able to show that nuclear exit occurs via the CrmA exportin. We conclude that sensing mechanisms discriminate between starvation and the presence of potential nutrients that can signal to the AreA transcription factor. Nitrogen source availability, but not quality, affects nuclear accumulation by regulating nuclear exit of AreA, providing a rapid response to changes in the supply of nutrients.

Active Transport, Cell Nucleus↗
PubMedDate not supplied

Long-term effect of total cycle time and aerobic/anoxic phase ratio on nitrogen removal in a sequencing batch reactor.

A laboratory-scale sequencing batch reactor was used to study nitrogen removal from a synthetic wastewater with an ammonium-nitrogen concentration of 50 mg/L. The effect of two key parameters (i.e., the total cycle time and the aerobic/anoxic phase duration ratio) on the performance of the reactor was investigated. Four sets of operational parameters resulting from the combination of 6 and 8 hours of cycle time and 1:1 and 1:3 aerobic/anoxic ratios were studied. Denitrification was based mainly on endogenous carbon sources as long as organic carbon, provided in the form of acetate, was quickly removed from the mixed liquor during the aerobic phase of the reactor operation. In terms of nitrogen removal efficiency, the set of 8 hours of cycle time and 1:3 aerobic/anoxic phase ratio was found to be superior in that it consistently yielded an effluent total nitrogen concentration of less than 15 mg/L (consisting almost exclusively of nitrate-nitrogen) and exhibited a percentage nitrogen removal rate of 77 +/- 2.5%. In terms of wastewater throughput (i.e., wastewater volume treated per day), however, the implementation of 6 hours of cycle time and 1:3 aerobic/anoxic phase ratio was satisfactory for nitrogen removal efficiency (72 +/- 2%), although elevated amounts of ammonium- and nitrite-nitrogen were found in the effluent. It was also demonstrated that under certain operating conditions nitrogen removal via nitrite is observed, as nitratification (i.e., oxidation of nitrite-nitrogen to nitrate) and denitratification (i.e., reduction of nitrate-nitrogen to nitrite) are bypassed.

Ammonia↗
PubMedDate not supplied

Nitrogen transformations modeling in subsurface-flow constructed wetlands.

Subsurface-flow constructed wetlands (CWs) wastewater treatment typically results in satisfactory organics removal. However, the removal of nutrients, particularly nitrogen, is often unreliable, and typically less than desired, and nitrogen transformations in wetlands systems are not well-understood. The principal objective of this study was to establish a basis for quantification of nitrogen transformations through subsurface flow CW systems. Actual performance data from a full-scale facility located near Lincoln, Nebraska, were used to calibrate a proposed nitrogen transformations model, which, in turn, was used to replicate and predict the wetlands performance. To realize this objective, a compartmental analysis technique, which uses a set of differential equations and nonlinear optimization numerical methods, was used for solving nitrogen transformation rates and for predicting wetland performance. The model satisfactorily reproduced the mean effluent concentrations for organic nitrogen, ammonium-nitrogen, and nitrate-nitrogen, but with lesser accuracy with respect to peak high and low effluent concentrations. Nitrogen mass balance in the wetland was used to identify likely nitrogen transformation pathways. Generally, it was found that approximately one-third of the influent nitrogen mass was removed through nitrification and denitrification, one-third was removed through vegetative assimilation, and the remainder was discharged in the wetland effluent.

Biodegradation, Environmental↗
PubMed2004

Management to reduce nitrogen losses in animal production.

Reduction of nitrogen loss in animal production requires whole-farm management. Reduced loss from one farm component is easily negated in another if all components are not equally well managed. Animal excretion of manure N can be decreased by improving the balance of protein or amino acids fed to that required by individual animals or animal groups or by improving production efficiency. Management to increase milk, meat, or egg production normally improves efficiency by reducing the maintenance protein required per unit of production. Large losses of manure nitrogen occur through the ammonia and nitrous oxide that are emitted into the atmosphere and the nitrate leached into groundwater. Up to half of the excreted nitrogen is lost from the housing facility, but this loss can be decreased through frequent manure removal and by avoiding deep litter systems and feedlots. Techniques such as acid treatment of manure, scrubbing of ventilation air, and floor designs for separating feces and urine substantially reduce ammonia emissions, but these practices are often impractical or uneconomical for general use. Manure storage units improve nutrient utilization by allowing better timing of nutrient application with crop needs. At least 70% of the nitrogen entering anaerobic lagoons is typically lost, but a less than 10% loss can be maintained using slurry storage with a natural crust or other cover, or by drying poultry manure to at least 50% dry matter. Irrigation and surface spreading of manure without soil incorporation often ensures the loss of all remaining nonorganic nitrogen (typically, 20 to 40% of remaining nitrogen). Rapid incorporation and shallow injection methods decrease this loss by at least 50%, and deep injection into the soil essentially eliminates this loss. For grazing animals, excessive loss can be avoided by not overstocking pastures and avoiding late fall and winter grazing. Reducing emissions between the animal and the soil can lead to greater leaching and denitrification losses from the soil if this additional nitrogen is not used properly. The use of a crop rotation that efficiently absorbs these nutrients and applying nitrogen near the time it is needed by crops reduce the potential for further loss. Maintaining the proper number of animals per unit of land available for manure application is always crucial for efficient recycling of nitrogen. Our understanding of nitrogen loss processes is improved through modeling, and computer models assist in the development of integrated systems for efficient and economical nitrogen use in animal production.

Amino Acids↗
PubMedDate not supplied

Clinical effect of blowing nitrogen gas across the cornea during photorefractive keratectomy.

OBJECTIVE: We evaluated the clinical effects of blowing nitrogen gas over the cornea during photorefractive keratectomy. METHODS: We retrospectively compared clinical outcomes of 32 patients (37 eyes), divided into two groups who had photorefractive keratectomy with nitrogen gas blowing across the cornea (n = 19) and without nitrogen gas (n = 18). All photorefractive keratectomies were performed between April 1991 and August 1992. Ablation zone diameters were 5.0 or 5.5 mm. The average attempted correction was -3.47 +/- 1.76 diopters (D) in the nitrogen gas group, and -3.48 +/- 1.25 D in the non-nitrogen gas group. RESULTS: The nitrogen gas group achieved more accurate corrections than the non-nitrogen gas group, but had a significantly greater amount of corneal haze at all postoperative examinations. Corneal haze was most evident at 1 month and gradually diminished therafter in both groups. At 6 months, videokeratography revealed a central island in 2 eyes (11.1%) of the non-nitrogen gas group. Because of undercorrection (2 eyes) or central island (1 eye), 3 out of 18 eyes in the non-nitrogen gas group were reablated 6 months later. CONCLUSIONS: The non-nitrogen gas group had more undercorrections and a higher frequency rate of central steep islands, but nitrogen gas blowing caused a greater amount of corneal haze.

Administration, Topical↗
PubMed2003

[The impact of land uses on watershed runoff nitrogen discharge in hilly regions].

Nitrogen is a crucial factor in causing the eutrophication of water body. Land use has an important impact on agricultural non-point sources (NPS) nitrogen discharge. This study on quantitative relationship of runoff nitrogen discharge and land use was conducted in Meicun watershed of Xuancheng County, Anhui Province, in the subtropical low hill area, by the dynamic monitoring of stream water and nutrient discharge, integrating interpretation of aerial image and GIS analysis. The results showed that, land use significantly affect nitrogen concentration and discharge in which nitrate nitrogen was the main component. There was a significant linear relationship between nitrate and total nitrogen concentration in the given land use system. However, statistically significant relationship between ammonium and total nitrogen concentration was found only in forest-pond system. Moreover, positive linear relationship existed between different forms of nitrogen discharge. It was found that there were exponential relationship between the discharge of nitrate, ammonium and total nitrogen and the area percentages of forest, pond, paddy and village. Forest and pond had a negative impact on nitrogen discharge while the paddy and village had positive effect. At the same time, land use types had important effect on nitrogen concentration.

Agriculture↗
PubMed2003

[Soil nitrogen mineralization and its prediction in winter wheat-summer maize rotation system].

The mineralization of soil nitrogen in winter wheat-summer maize growth season was studied with field experiment, and its prediction was made by interval leached aerial incubation combined with first-order dynamic model. The results showed that the amount of soil mineralized nitrogen had a large variation among years and crops. The soil nitrogen mineralization was lower in winter wheat growth season than in summer maize growth season, resulted in the yield increment of summer maize being not significant with increasing nitrogen fertilization rate. The amount of soil mineralized nitrogen occupied 31%-60% of the total nitrogen uptake by winter wheat and 62%-108% by summer maize. It was understandable why crop yield (especially summer maize) was not significantly response to applied nitrogen fertilizer. The amount of soil mineralized nitrogen decreased with increasing soil nitrogen supply. The mineralization was positive in normal nitrogen supply range(0-300 kg N.hm-2). The first order dynamic model could only predict the whole trend of mineralization in growth season, but could not reflect its variation in some growth stages. The role of the model was still important in view of the prediction of nitrogen mineralization before sowing.

Crops, Agricultural↗
PubMed2005

The development of policy approaches for reducing nitrogen pollution to coastal waters of the USA.

Two-thirds of the coastal rivers and bays in the United States are degraded from nutrient pollution, and nitrogen inputs these waters continue to increase. The nitrogen comes from a variety of sources, including runoff from agricultural fields, concentrated animal feeding operations, atmospheric deposition from fossil fuel combustion, and sewage and septic wastes. Technical solutions for nitrogen pollution exist at reasonable cost. That most of these solutions have not yet been implemented to any significant extent across the United States suggests that new policy approaches are necessary. The best solution may involve a combination of voluntary and mandatory approaches, applying different approaches to different sources of nitrogen pollution. A watershed-based approach that relies heavily on voluntary mechanisms (such as crop-yield insurance to reduce over-fertilization) is likely to be the most effective for some sources of nitrogen (such as runoff from agricultural fields), while a uniform national regulatory approach may be better for others (such as NOx emissions from fossil fuel combustion). Implementation of management strategies should be carefully coupled to monitoring programs to assess the effectiveness of these strategies. While both nitrogen and phosphorus are important to control, the focus should be on nitrogen management, in part because nitrogen is more generally the causal agent of coastal eutrophication. Also, while nitrogen-control practices tend to also reduce phosphorus pollution, phosphorus-control practices often have little effect on nitrogen. Although current scientific and technical knowledge is sufficient to begin to make substantial progress toward solving coastal nitrogen pollution, progress will be made more quickly and more cost effectively with increased investment in appropriate scientific research.

Animals↗
PubMed2006

[Effects of nitrogen application rate and its basal-/top-dressing ratio on spatio-temporal variations of soil NO3- -N and NH4+ -N contents].

Under high-yielding cultivation condition, this paper studied the spatiotemporal variations of soil NO3 -N and NH4+ -N contents as affected by different nitrogen application rate and its basal-/top-dressing ratio, and calculated the apparent budget of soil nitrogen at different growth stages of wheat. The results indicated that compared with split application, applying all fertilizer nitrogen at jointing stage decreased the soil NO3- -N content and apparent surplus of soil nitrogen before jointing stage, and decreased the nitrogen leaching to deeper soil layers. Applying fertilizer nitrogen at flagging stage had no significant difference with split application in soil NO3- -N content, but increased soil NH4+ -N content. Applying fertilizer nitrogen at maturing stage increased the soil NO3- -N content in 0-60 cm and 0-20 cm layers. In comparing with applying 240 kg x hm(-2) of fertilizer nitrogen at jointing stage, applying 168 kg x hm(-2) of fertilizer nitrogen at the same stage decreased the soil NO3- -N and NH4+ -N contents at flagging stage, soil nitrogen deficit from flagging to maturing stage, and soil NO3- -N content at maturing stage. The grain yield and its protein content had no significant difference among different treatments, but applying all 168 kg x hm(-2) fertilizer nitrogen at jointing stage induced the highest grain protein content.

Fertilizers↗
PubMed1989

Nitrogen metabolism in man under hypokinesia and physical exercise.

Experimental studies of hypokinetic physiology are generally based on the assumption that diminished muscular activity (progressive reduction of number of steps per day) is hostile to animal and human organisms, since the entire animal kingdom has been formed in a high motor activity environment, which left its imprint on the evolution, structure, function and behavior of living organisms. It has been suggested that physical exercise may be used to prevent changes in man's nitrogen metabolism under hypokinesia. Thus, the aim of this study was to evaluate the effect of physical exercise in attenuating nitrogen metabolic changes under hypokinesia of 90 days in twelve healthy men aged 19 to 23 years. They were divided into two groups with six men in each. The control group was subjected to pure hypokinesia, that is, without the use of any preventive measures, and the experimental group was submitted to combined hypokinesia and physical exercise with energy expenditure of about 500 kcal. For the simulation of the hypokinetic effect the men were kept under an average of 500 steps/day. The caloric value of their diet was about 2400 kcal/day and 2600 kcal/day for the control and experimental groups, respectively. Total nitrogen, urea nitrogen, nitrogen ammonium salts, nitrogen of free amino acids, creatine, creatinine, as well as vitamins C, B1 and 4-pyridoxic acid excretion were measured in urine. Hypokinesia induced a negative nitrogen balance, which was most pronounced in the control group. The excretion of the other nitrogeneous compounds, vitamins, creatine, and creatinine was also increased. Physical exercise had only a limited effect on nitrogen metabolism. We concluded that diminished muscular activity induced a marked increased excretion of nitrogen; at the same time it was revealed that physical exercise cannot be used to counteract effectively the development of adverse reactions of nitrogen metabolism under hypokinetic conditions.

Adult↗
PubMed1988

Modulation of pulmonary defense mechanisms against viral and bacterial infections by acute exposures to nitrogen dioxide.

The scientific literature suggests that ambient levels of nitrogen dioxide increase susceptibility to respiratory infections. However, this association has not been conclusively demonstrated. The epidemiologic data regarding this relationship are inconclusive because these studies have used parameters of "acute respiratory illness" that are not necessarily related to infectious episodes. Previous animal studies have used either mortality after bacterial infection with virulent bacteria or decreased rate of intrapulmonary killing of bacteria with low virulence. Studies using appropriate bacterial and viral challenge organisms, with morbidity as an endpoint, provide a better basis for extrapolation to humans. The investigations in animals suggest a relationship between nitrogen dioxide and increased susceptibility to respiratory infection, but studies in which functional parameters of host resistance to such infections have been used are few. The aim of this work was to determine the threshold level of acute nitrogen dioxide exposure that would induce increased susceptibility to, and increased severity of, viral and bacterial infections. Physiologic parameters of host resistance to respiratory infections were used as endpoints. A composite picture was developed of dose-response relationships between nitrogen dioxide and the impairment of a spectrum of defense parameters in the murine respiratory tract against viral and bacterial challenges. The salient findings of this study are as follows: (1) the intrapulmonary killing of Staphylococcus aureus was impaired at 5 ppm of nitrogen dioxide; (2) this effect was found at 2.5 ppm or less when nitrogen dioxide exposure was superimposed on lungs predisposed to lowered resistance through immunosuppression with corticosteroids; (3) the adverse effect of nitrogen dioxide occurred at lower concentrations when exposure followed bacterial challenge; and (4) during the course of murine Sendai virus infection, exposure to nitrogen dioxide for four hours per day did not alter the infection in the lungs, but rather it enhanced lung pathology. The implications of these findings are that the antibacterial defenses of the lungs are susceptible to the inhibiting effects of short acute exposures of lower concentrations of nitrogen dioxide when the lungs are predisposed by bacteria present or, even more so, by immunosuppression. The alveolar macrophage phagocytic system is the defense component of the lungs that is most susceptible to the adverse effects of nitrogen dioxide. The finding that nitrogen dioxide increases virus-associated lung damage suggests that the increased severity of the disease process results from the proliferation of the virus to high titers, rather than from alterations of the infective process.

Animals↗
PubMed1979

[Comparative study of postoperative nitrogen balance as a function of carbohydrate intake].

Postoperative nitrogen intake, which limits nitrogen catabolism and improves conditions of healing, classically implies a high calorie intake. The risks and dangers of hypertonic or hypersmotic solutions are such that the provision of nitrogen postoperatively in ordinary surgery is often avoided. The authors studied postoperative nitrogen balance for a given nitrogen intake with different calorie levels in a series of 50 patients undergoing digestive surgery. A first group (28 patients--mean age 54.6 years, mean weight 63.3 kg) received 12.4 g of nitrogen and 1000 calories per day. The second group (22 patients--mean age 52.5 years, mean weight 64.7 kg) received 12.4 g of nitrogen and 2200 calories. Daily nitrogen balance was calculated using the method of approximation described by Apfelbaum on the basis of urinary urea excretion. Statistical study of nitrogen balances for the first four days showed no statistically significant difference between the mean values in the two groups. For group A, the cumulative balance for the first four days was 7.60 g +/- 4.75 g, and for group B 7.85 G +/- 6.64 g. Limitation of postoperative nitrogen catabolism does not necessarily impose the need for high calorie intake, implying the use of a central venous catheter and administration at constant flow. The patient undergoing ordinary digestive surgery may benefit from postoperative nitrogen supplies, associated with a moderate calorie intake and administered via usual venous routes.

Adult↗
PubMed1977

[Relationship between the volatile fatty acids (VFA) in the rumen and nitrogen secretion into isolated sheep's rumen].

Two sheep with a ruminal fistula and an isolated small rumen were studied for the secretion of ammonia nitrogen, urea nitrogen, and amino nitrogen into the isolated rumen at different levels of volatile fatty acids (VFA) (50, 133-97, and 97-66 M Mol 1(-1)) in the rumen. The VFA level in the rumen was found to exert a great influence on the quantitative secretion of endogenous nitrogen from the blood through the rumen wall into rumen content. When the VFA level in the rumen was increased by administration of a single dose of acetic, propionic, and butyric acid, the secretion of ammonia nitrogen and amino nitrogen abruptly dropped and the secretion of urea into the isolated rumen slightly increased. The over-all amount of nitrogen (NH3-N + urea-N + amino-N) that had passed into the isolated rumen in the course of an hour showed a highly significant correlation with the passage of nitrogen in the form of ammonia and amino nitrogen and was greatest before the application of VFA to the rumen, i.e. at the level of 50 m mol 1-1. Of the metabolites under study, which were passing to the isolated rumen, amino nitrogen shared the greatest proportion (45.38-46.54%). When the VFA level in the rumen was raised, the proportion of ammonia secreted to the isolated rumen decreased and the proportion of urea in the total amount of nitrogen increased.

Animals↗
PubMed1993

[Experimental study of fecal excretion of nitrogen in different nutritional conditions].

Fecal nitrogen excretion in different nutritional conditions were studied in 32 adult Wistar rats, casually distributed in four groups: group A (12), with normal control rats; group B (6), with subcutaneous impalnt of Walker-256 carcinosarcoma, at the beginning of the experiment; group C (8), with tumor implant eight days before the experiment beginning; group D (6), with standard skin wound in 15th day. The animals were fed with normoproteic diet (25% casein content). Nitrogen ingestion and urinary and fecal excretion were daily measured. Evaluation selected parameters were: nitrogen ingestion and urinary, fecal and total excretion; nitrogen fecal excretion/ingestion, nitrogen fecal excretion/urinary excretion and nitrogen fecal excretion/total excretion ratios; nitrogen urinary excretion/ingestion and nitrogen urinary excretion/total excretion ratios. Adequate statistical analysis was done with p < 0.05 critical limit value. It was observed that in normal animals nitrogen fecal excretion was equal to 5.7% ingestion value, 12.0% urinary excretion and 10.8% total excretion. In presence of malignant tumor, nitrogen fecal excretion was equal to 79% of normal animals value. In rats with skin wound in cicatrization nitrogen fecal excretion was 70.5% of normal animals value.

Animals↗