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PubMed1991

Transcriptional regulation of cytochrome d in nitrogen-fixing Azotobacter vinelandii. Evidence that up-regulation during N2 fixation is independent of nifA but dependent on ntrA.

Cytochrome d has been postulated to be the "respiratory protection" oxidase of Azotobacter vinelandii, allowing this organism to fix nitrogen under aerobic growth conditions. We have previously cloned and characterized the structural genes for the A. vinelandii cytochrome d (cydA and cydB). The cyd genes are co-transcribed, yielding an mRNA of approximately 3.6 kilobase pairs. The level of the cyd message was 2-3-fold higher in cells that were fixing nitrogen, as compared with non-nitrogen-fixing cells. RNase protection analysis was used to determine the transcriptional start site at 275 bases upstream of the initiator ATG of cydA, and this start site was the same for nitrogen-fixing and non-nitrogen-fixing cells. The cyd promoter has sequence similarities to the canonical Escherichia coli promoters, which are transcribed by the major sigma 70 form of RNA polymerase. Plasmid-borne lacZ transcriptional fusions were constructed, using approximately 650 base pairs of 5'-upstream sequences of the cyd structural genes. This region had a strong promoter activity which was further up-regulated 1.5-2.5-fold upon the induction of nitrogen fixation. The cyd-lacZ fusions were characterized in a nifA- as well as an ntrA- background. Mutations in neither of these nif regulatory genes affected the constitutive expression of cyd under non-nitrogen-fixing conditions. However, the up-regulation of this promoter during the induction of nitrogen fixation was abolished only in the ntrA- background. Based on these results, the cytochrome d promoter of A. vinelandii belongs to a new class of nitrogen-regulated promoters which, unlike the authentic nif genes, does not require the ntrA gene product for its expression. The up-regulation of this promoter during nitrogen fixation, however, requires the ntrA gene product.

Amino Acid Sequence↗
PubMed1991

Mechanisms of nitrogen dioxide toxicity in humans.

These studies were undertaken to evaluate short-term respiratory effects and identify markers of nitrogen dioxide toxicity during exposures designed to approximate realistic conditions. With the development of bronchoalveolar lavage as a clinical investigative technique, the evaluation focused on the assessment of effects induced at the alveolar level. The exposure protocols were designed to assess the duration of nitrogen dioxide-induced effects and determine exposure-response relationships. Groups of normal, nonsmoking volunteers of both sexes between the ages of 18 and 40 years, without airway hyperreactivity, constituted the study population. The exposure protocols required a total of three to five days for each subject, depending on the timing of bronchoalveolar lavage. Subjects were exposed to nitrogen dioxide or air for three hours in a double-blind, randomized fashion in a 45-m3 environmental chamber, with intermittent exercise sufficient to quadruple minute ventilation. Pulmonary function was measured during and after exposure, and airway reactivity to carbachol was assessed before and after exposure. Lavaged cells were examined for their capacity to inactivate influenza virus and secrete IL-1 in vitro. Cell-free lavage fluid was analyzed for total protein, albumin, alpha 2-macroglobulin, arylsulfatase, and alpha 1-protease inhibitor. The studies were undertaken in three phases, each of approximately one year's duration. In Phase 1, 15 subjects were exposed to a background concentration of 0.05 parts per million2 (ppm) nitrogen dioxide and to three 15-minute peaks of 2.0 ppm, and underwent bronchoalveolar lavage 3.5 hours after nitrogen dioxide exposure. During Phase 2, 8 subjects were exposed to continuous 0.60 ppm nitrogen dioxide and underwent bronchoalveolar lavage 18 hours later. Finally, in Phase 3, 15 subjects were exposed to continuous 1.5 ppm nitrogen dioxide and underwent bronchoalveolar lavage 3.5 hours after exposure. No significant symptomatic or pulmonary function changes could be detected in response to any of the nitrogen dioxide exposures. However, a small but significant increase in airway reactivity was observed in normal subjects after exposure to 1.5 ppm nitrogen dioxide. Following the highest dose of carbachol (10 mg/mL), the forced expiratory volume in one second decreased 7.5 +/- 1.1 percent after nitrogen dioxide exposure compared to 4.8 +/- 1.1 percent after exposure to air (p less than 0.05). No symptoms were induced in any of the groups by the carbachol exposures. Analyses of cells recovered by bronchoalveolar lavage during all three phases revealed no differences in total cell recovery, cell viability, or differential cell counts.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1990

Influence of postnatal age on nitrogen metabolism in very low birth weight infants appropriate for gestational age.

In 14 very low birth weight (VLBW) infants appropriate for gestational age the absorption and retention of nitrogen and the energy balance were studied on the 8th day and the 6th week of postnatal age. All infants were fed with a human milk formula composed by fresh mother's milk enriched with 6 g freeze-dried human milk/100 ml. The absorption rates of nitrogen and fat increase significantly with postnatal age but even on the 8th day of life they are on high levels (nitrogen absorption: 86.9 +/- 3.2% of intake; fat absorption: 85.7 +/- 4.3% of intake). Despite the higher nitrogen absorption during the 6th week of life the excretion of total nitrogen is lower in comparison to the 8th day of life. Similarly, the percentages of alpha-amino-nitrogen and of ammonium-nitrogen of the total nitrogen excretion in the urine decrease whereas the percentage of urea-nitrogen increases with postnatal age. The results indicate a postnatal development of both the digestive, as well as the metabolic capacity. The postnatal adaptation of the metabolic capacity to utilize nitrogen seems to be the stronger limiting factor for nutrition than the functional capacity of digestion and absorption. Thus, metabolic monitoring is essential for the individual nutrition of VLBW-infants during the first weeks of postnatal life. Urine analysis data are very sensitive for evaluating the metabolic state of these infants.

Aging↗
PubMed1987

Effects of increasing glucose intake on nitrogen balance and energy expenditure in malnourished adult patients receiving parenteral nutrition.

The effects of increasing glucose intake on nitrogen balance, energy expenditure and fuel utilization were measured in malnourished adult patients receiving parenteral nutrition with constant nitrogen intake and high or low glucose intakes for 8 day periods. Energy balance, nitrogen balance, weight and temperature were determined daily. Blood samples taken at admission and at the end of days 7 and 8 of each diet were analysed for glucose, fatty acids, urea, insulin, glucagon and thyroid hormones. The effect of increasing glucose intake was to increase nitrogen balance by 0.28 +/- 0.08 (SEM) mg/kJ. A scheme is proposed, based on present and previous findings, of the separate effects of nitrogen and energy intake on nitrogen balance, permitting calculation of rates of repletion of fat and lean body mass from estimates of nitrogen intake and energy balance. Malnourished patients are shown to attain markedly positive nitrogen balances at zero or negative energy balances. Large errors in estimation of energy requirements have little effect on nitrogen balance. Changes in nitrogen balance were entirely due to changes in urea excretion. Creatinine excretion increased 12% with high glucose intake, attributed mainly to increased muscle mass (7%) and body temperature (4%). A 12% increase in resting energy expenditure was only partly due to costs of glycogen storage and lipogenesis; the remainder, about one-half, is probably due to glucose and insulin mediated increases in sympathetic activity. There were marked increases in 3,5,3'-triiodothyronine (T3) concentrations with time, but no difference between the high and low glucose diets. The T3/thyroxine ratio, an index of free T3 concentration, increased much more rapidly on the high than on the low glucose diet. Changes in T3 could not account for the effect of glucose, under these conditions, to increase resting energy expenditure.

Adult↗
PubMed1984

Effect of lipid-coated lysine on digestion and nitrogen metabolism by wethers.

Four mature wethers (70 kg) fitted with permanent abomasal cannulas were assigned to a 4 X 4 Latin square design to study the effect of coating supplemental lysine with coconut oil on nutrient digestion, nitrogen retention and recovery of amino acids in the abomasum and plasma. Dietary treatments were: Control (C) = basal diet; Lysine (LYS) = Control + 1% supplemental lysine; Coconut oil-coated lysine (CN-LYS) = Control + 1% supplemental lysine coated with coconut oil; and Coconut oil + diet (CN-DIET) = Control + 1% supplemental lysine + an equal amount of coconut oil added to the entire diet. Lysine supplementation significantly increased total apparent dry matter, ether extract and energy digestibilities. Total nitrogen and protein nitrogen flows to the abomasum were decreased (p less than .1) in lambs consuming CN-LYS and CN-DIET compared with LYS. Urinary nitrogen excretion (p less than .05), ruminal ammonia nitrogen and plasma urea nitrogen (p less than .05) concentrations were higher for LYS, CN-LYS and CN-DIET compared with C and highest for CN-LYS. There were no differences in nitrogen retention among treatments. Recovery of lysine in the diets after coating (CN-LYS) or lipid addition (CN-DIET) was reduced indicating degradation of supplemental lysine to other nitrogenous compounds during the coating process or storage since total dietary nitrogen content was equivalent to LYS. Flow of abomasal lysine (% of lysine intake) was higher (p = .15) for CN-LYS and CN-DIET than LYS. Flow of total essential amino acids (% of total amino acid flow) was greater (p less than .02) when lysine was added to diets. Essential amino with LYS. Plasma amino acid concentrations did not differ among treatments. Coating lysine with coconut oil did not protect the amino acid from ruminal degradation and was ineffective in improving total nitrogen status of mature wethers.

Abomasum↗
PubMed1980

Studies on calorie to nitrogen ratio for total parenteral nutrition.

In this study, three calorie nitrogen ratios, 102:1, 163:1 and 204:1, were analyzed in 40 week long study periods in a total of approximately 22 stable patients without sepsis who required parenteral nutrition. A calorie to nitrogen ratio of 163:1 appeared to be most efficacious for nitrogen equilibrium in these patients studied. A calorie to nitrogen ratio of 102:1 was associated with weight loss and negative nitrogen balance. Conversely, increasing the calorie to nitrogen ratio to 204:1, at least for this group of patients, did not result in improved nitrogen retention. Different methods of calculation of nitrogen equilibrium are presented, depending upon the disease state and the method by which data analysis is carried out. The results suggest that different levels of nitrogen and caloric input as well as calorie to nitrogen ratio may be appropriate in different disease states.

Adult↗
PubMedDate not supplied

[Changes in nitrogen metabolism in young cattle following ultraviolet irradiation and feeding on urea].

Some indexes of nitrogen metabolism in blood, rumen content and urine of bull-calves fed on urea were studied as affected by UV-radiation. The content of protein, nonprotein, amine nitrogen, urea and ammonia in the rumen content and blood as well as as intensity of urea nitrogen and ammonia excretion with urine were determined. It is established that when 25% of protein necessary for the organism was replaced in the ration by urea, UV-radiation with a dose of 120 merg/h-m2 lowers already at the beginning of irradiation the amount of amine nitrogen and further the protein one in the young cattle rumen content. In blood of the irradiated bull-calves at the beginning of irradiation the level of amine nitrogen decreases, the level of nonprotein nitrogen lowers with a longer irradiation. The content of protein nitrogen in blood at that time increases. It was found that the content of ammonia in the bull-calves rumen during the first twenty-hours lowers, the amount of urea in blood does not change essentially. Simultaneously the ammonia excretion with urine intensifies, at the same time the excretion of urea nitrogen with urine does not differ essentially from that in the control bull-calves. In the bull-calves under study the nitrogen balance and average daily gains increase that may testify to the fact that UV-radiation in the applied dose stimulates a more complete utilization of urea nitrogen for the synthesis processes in the organism.

Animal Feed↗
PubMedDate not supplied

Loss of nitrogen by denitrification.

A series of experiments showed the quantity and composition of nitrogen lost in gaseous form from fertilizers in soil is largely determined by the conditions of denitrification. Loss of nitrogen from ammonium sulfate or calcium nitrate was mainly through the release of nitrous oxide and molecular nitrogen, while nitrogen was released from sodium nitrite in the form of nitric oxide. Under anaerobic conditions and at neutral soil pH in the presence of glucose, the more reduced gaseous forms of nitrogen were released. However, the oxides of nitrogen predominated under conditions unfavorable for denitrification. The nitrogen oxides were not the terminal products of nitrogen conversion (nitrates and nitrites). By a process of dissimilation, the nitrogen oxides acted as electron acceptors for microorganisms, being converted to N2O and N2. The reduction of NO generally led to the formation of N2O as an intermediate, and depended on pH, aeration, and the presence of an energy source for the denitrifying organisms.

Aerobiosis↗
PubMed2002

Could microbial symbionts of arthropod guts contribute significantly to nitrogen fixation in terrestrial ecosystems?

Fixed nitrogen is a limiting nutrient in most terrestrial ecosystems and has been assumed to be supplied almost entirely by free-living bacteria as well as by bacteria living in association with plants. The survival and growth of many arthropods on diets with extremely high carbon to nitrogen (C:N) ratios suggest that these arthropods are not obtaining sufficient nitrogen from their diets but must be obtaining additional nitrogen from some other source(s). Estimates of N(2) fixation have suggested that symbiotic microbes of some arthropod hindguts could be obtaining this additional nitrogen as a result of nitrogen fixation. With the recent availability of antibody and nucleic acid probes, the presence of the enzyme that reduces dinitrogen gas to ammonia (nitrogenase) as well as the presence of its transcripts can be detected and localized with great sensitivity. A preliminary survey of a few detritivores indicates that nitrogen-fixing microbes of diverse forms are widespread in arthropod hindguts. In calculating nitrogen budgets, the possible contributions of nitrogen fixation by symbionts in arthropod guts, however, has been largely ignored. N(2) fixation in arthropod guts, with rates as high as 10-40 kg/ha/year being possible, may represent a significant contribution both to the growth of arthropods and to their ecosystem functions of processing carbon and nitrogen.

Journal Article↗
PubMed1976

Hydrogen evolution: A major factor affecting the efficiency of nitrogen fixation in nodulated symbionts.

Nitrogenase-dependent hydrogen evolution from detached legume nodules and from reaction mixtures containing cell-free nitrogenase has been well established, but the overall effect of hydrogen evolution on the efficiency of nitrogen fixation in vivo has not been critically assessed. This paper describes a survey which revealed that hydrogen evolution is a general phenomenon associated with nitrogen fixation by many nodulated nitrogen-fixing symbionts. An evaluation of the magnitude of energy loss in terms of the efficiency of electron transfer to nitrogen, via nitrogenase, in excised nodules suggested that hydrogen production may severely reduce nitrogen fixation in many legumes where photosynthate supply is a factor limiting fixation. With most symbionts, including soybeans, only 40-60% of the electron flow to nitrogenase was transferred to nitrogen. The remainder was lost through hydrogen evolution. In situ measurements of hydrogen evolution and acetylene reduction by nodulated soybeans confirmed the results obtained with excised nodules. In an atmosphere of air, a major portion of the total electron flux available for the reduction of atmospheric nitrogen by either excised nodules or intact nodulated plants was utilized in the production of hydrogen gas. Some non-leguminous symbionts, such as Alnus rubra, and a few legumes (i.e., Vigna sinensis) apparently have evolved mechanisms of minimizing net hydrogen production, thus increasing their efficiency of electron transfer to nitrogen. Our results indicate that the extent of hydrogen evolution during nitrogen reduction is a major factor affecting the efficiency of nitrogen fixation by many agronomically important legumes.

Journal Article↗
PubMed1966

Effects of calcium deficiency on symbiotic nitrogen fixation.

The mechanism of the effect of mild calcium deficiency on nitrogen metabolism of the symbiotic plant was studied from the distribution of calcium and of nitrogen and carbohydrate fractions in plant organs.Nitrogen concentrations of all plant organs decreased with calcium deficiency. Addition of either a nitrogen or a calcium salt increased nitrogen concentrations. For roots as well as whole plants the effects of one salt were largely replaced by the other. These effects establish that calcium deficiency decreased the supply of fixed nitrogen from nodules to other organs. As weight of nodules was independent of calcium it follows that nodular efficiency was impaired.Since nitrogen concentrations of nodules decreased rather than increased with calcium deficiency it is suggested that calcium deficiency interferes with the rate of reduction of nitrogen in the nodule rather than with the export of reduced nitrogen. Distribution of alpha-amino, amide, and ammonium nitrogen are consistent with this suggestion.Nitrogen fixation was not limited by translocation of carbohydrates to nodules as calcium deficiency had little effect on the concentration of soluble carbohydrates and actually increased the concentration of starch in nodules.Calcium deficiency depressed the calcium content of nodules so that nitrogen fixation may have been impaired by inadequate calcium for nodular structure or metabolism.

Journal Article↗
PubMed1986

Regulation of Carbon Flow by Nitrogen and Light in the Red Alga, Gelidium coulteri.

The red alga Gelidium coulteri Harv. photosynthetically fixed [(14)C] bicarbonate at high rates under defined conditions in unialgal laboratory culture. The fixation rate and flow of photosynthate into various end products were dependent on the nitrogen status of the tissue. Plants fed luxury levels of nitrogen (approximately 340 micromolar) showed fixation rates several-fold higher than those seen for plants starved for nitrogen. The addition of NO(3) (-) or NH(4) (+) to such starved plants further inhibited fixation over at least the first several hours after addition. The majority of (14)C after incubations of 30 minutes to 8 hours was found in the compounds floridoside, agar and floridean starch. In addition, amino acids and intermediate compounds of the reductive pentose phosphate pathway, glycolytic pathway and tricarboxylic acid cycle were detected. Nitrogen affected the partitioning of labeled carbon into these compounds. Plants under luxury nitrogen conditions had higher floridoside levels and markedly lower amounts of agar and starch than found in plants limited for nitrogen. Amino acid, phycobiliprotein and chlorophyll levels were also significantly higher in nitrogen-enriched plants. Addition of NO(3) (-) to starved plants led to an increase in floridoside, tricarboxylic acid cycle intermediates and amino acids within 1 hour and inhibited carbon flow into agar and starch. Carbon fixation in the dark was only 1 to 7% of that seen in the light. Dark fixation of [(14)C]bicarbonate yielded label primarily in tricarboxylic acid cycle intermediates, amino acids and polysaccharides. Nitrogen stimulated amino acid synthesis at the expense of agar and starch. Floridoside was only a minor component in the dark. Pulse-chase experiments, designed to show carbon turnover, indicated a 2-fold increase in labeling of agar over 96 hours of chase in the light. No increases were seen in the dark. Low molecular weight pools, including floridoside, decreased 2- to 5-fold over this period under both light and dark conditions. Nitrogen status did not influence turnover. There was little or no organic carbon released into the culture medium over this period. The results are consistent with biosynthetic pathways to floridoside and agar that share the common intermediate UDP-d-galactose. It is hypothesized that synthesis of floridoside is regulated by nitrogen and light at the enzymic level.

Journal Article↗
PubMed1997

Urate deposits in the gecarcinid land crab Gecarcoidea natalis are synthesised de novo from excess dietary nitrogen

The urate content of the gecarcinid land crab Gecarcoidea natalis was correlated to the amount of nitrogen assimilated. Crabs fed a high-nitrogen diet (ad libitum amounts of soy beans and fig leaves, Ficus macrophylla) for 6 weeks assimilated approximately 23 times more nitrogen (33.9±5.6mmolkg-1day-1) than animals fed a diet low in nitrogen (fig leaves alone) (1.5±0.7mmolkg-1day-1). Animals maintained on a high-nitrogen diet accumulated urate (67.1±29.4mmolkg-1drymass), while animals fed the low-nitrogen diet did not accumulate significant amounts of urate compared with the control animals killed at the beginning of the dietary period. The urate deposits clearly originate from the excess dietary nitrogen ingested on the high-nitrogen diet. The intake of preformed dietary purine was low (0.028±0.005mmolkg-1drymass) and at most could only account for 0.04% of the urate accumulated by crabs fed the high-nitrogen diet. This indicates that the urate was synthesised de novo. When crabs were fed a high-nitrogen diet supplemented with [15N]glycine, the 15N heavy isotope was incorporated into urate. This provided direct evidence that the urate was synthesised de novo.

Journal Article↗
PubMed1981

[Amide nitrogen in blood plasma of sheep].

The physiological concentrations of amide nitrogen in blood plasma of sheep taken before feeding, 60, 180, and 360 min, after feeding were determined. The concentration of the total amide nitrogen in plasma at intake of 7.6 g of nitrogen per day (45.55 +/- 3.85 mmol.1-1) was significantly higher (P less than 0.001) than at intake of 24 g of nitrogen per day (42.34 +/- 4.07 mmol.1-1). Between the concentrations of amide nitrogen unbound to plasma proteins (1.5 +/- 1.36 mmol.1-1) no significant differences in dependence on the nitrogen intake were found. The results prove that a substantial part of amide nitrogen in plasma is bound to proteins and that its level is relatively stable. A significant change was observed only in the concentration of the total amide nitrogen after a long-term feeding of sheep with some other diet. When the concentration of the total amide nitrogen in plasma was lower in relation to nitrogen intake, the urea concentration was higher.

Amides↗
PubMed2006

Global transcriptional analysis of Methanosarcina mazei strain Gö1 under different nitrogen availabilities.

Certain archaeal species can fix molecular nitrogen under nitrogen limiting conditions although little is known about this process at either the genetic or molecular level. To address this on a genome-wide scale, transcriptional analysis was performed on the model methanogen Methanosarcina mazei strain Gö1 using DNA-microarrays. The genomic expression patterns for cells grown under nitrogen fixing conditions versus nitrogen sufficiency (10 mM ammonium) revealed that approximately 5% of all genes are differentially expressed. Besides a small set of genes previously known to be up-regulated under nitrogen limitation, 14 additional genes involved in nitrogen metabolism were identified plus 10 genes encoding potential transcriptional regulators, 13 genes involved in carbon metabolism, 3 genes in general stress response, 8 putative transporter genes, and an additional 21 genes with unknown function. Quantitative reverse transcriptase PCR experiments confirmed the differential expression of a subset of these genes. Promoter analysis revealed a palindromic DNA motif centered nearby the transcriptional start point for several genes up-regulated under nitrogen limitation. A bioinformatics study demonstrated the presence of this motif in the up-stream region of 52 genes genome-wide, the majority of which showed nitrogen dependent differential transcription. We therefore hypothesize that this DNA element is involved in nitrogen control in M. mazei where it may act as a binding site for a regulatory protein.

Archaeal Proteins↗
PubMed2002

Effects of long-term oral misoprostol administration on hepatic amino acid-nitrogen metabolism in patients with cirrhosis.

BACKGROUND: The acute infusion of a Prostaglandin of E series 1 (PGE1) analogue results in nitrogen sparing in cirrhosis. AIMS: To test the effects of long-term oral PGE1 on hepatic and whole-body nitrogen metabolism. PATIENTS AND METHODS: Ten patients with advanced cirrhosis were studied in paired experiments, before and 30-50 days after oral misoprostol therapy. alpha-Amino-nitrogen levels and urea-nitrogen synthesis rate were measured in the post-absorptive state and in response to continuous alanine infusion (2 mmol/kg per hour for 4.5h). Data were used to compute the functional hepatic nitrogen clearance, i.e. the slope of the regression of alpha-amino-N levels to urea-N synthesis rate, and the apparent nitrogen exchange. RESULTS: Misoprostol reduced urea-N synthesis rate (during fasting and in response to alanine), resulting in a positive nitrogen exchange. The functional hepatic nitrogen clearance slightly increased, and the regression line was rightwards shifted, indicating a reduced urea synthesis rate at any alpha-amino-N concentration. Amino acid- and ammonia-N did not accumulate in plasma. No systematic effects on insulin and glucagon were observed. CONCLUSIONS: Data are consistent with a nitrogen sparing mechanism of misoprostol, not mediated by hormone levels. These effects may be beneficial in clinical hepatology, and need to be tested in controlled trials.

Administration, Oral↗
PubMed1978

Effect of moisture level on nitrogen immobilization as affected by wheat straw decomposition in soil.

Samples of a slightly degraded chernozem soil were amended with 2 per cent of wheat straw at three moisture levels (10, 20, and 30 per cent) and were provided with 160, 240, and 400 ppm of ammoniacal nitrogen. Amounts of total, ammonia, and nitrate were determined at different periods of incubation at 28 degrees C and immobilization of the total available nitrogen in the soil was calculated. Substantial amounts of the added nitrogen were immobilized in the soil as a result of the straw decomposition during the first month of incubation. The amount of inorganic nitrogen (NH4 + -N + NO3 - -N), bound within 75 days of incubation, was almost three times less than that immobilized within 30 days. Maximum quantity of nitrogen was immobilized at 30 and 20 per cent moisture levels at 30 and 75 days of incubation, respectively. Minimum immobilization was observed at 10 per cent moisture at almost all levels of nitrogen. The absolute amount of nitrogen immobilized increased in proportion to the quantity of nitrogen added, but the relative immobilization tended to decrease with the increased inorganic nitrogen the soil.

Humidity↗
PubMed1981

Nitrogen and urea metabolism during continuous ambulatory peritoneal dialysis.

During continuous ambulatory peritoneal dialysis (CAPD), concentrations of serum urea nitrogen (SUN) have been reported that are lower than what would be predicted from estimated dietary protein intake and the calculated urea clearance by dialysis. Net urea generation (urea nitrogen appearance) and losses of various nitrogenous constituents were measured during 12 metabolic studies in patients undergoing CAPD. Patients ingested constant diets containing either 1.0 or 1.4 g or protein per kilogram of body wt per day; total daily urea "clearance" from peritoneal dialysis plus renal clearance averaged 10.8 +/- 0.3 liters/day. Urea nitrogen appearance was only 55 and 68% of total nitrogen output with the low and high protein diets, respectively, values that are substantially lower than those reported in normal subjects, patients with chronic renal failure, and those undergoing hemodialysis. The reduction fraction of nitrogen appearing as urea was largely accounted for by the loss of protein and free amino acids into the dialysate. These respective constituents accounted fro 11.5 and 4.4% of total nitrogen output. Urea nitrogen appearance correlated closely (r = 0.96) with total nitrogen output in the patients undergoing CAPD.

Adult↗