Urea Degradation Rate Research Articles

Structure engineering and surface reconstruction enabling MoNi4 hollow nanocube for efficient urea-assisted water electrolysis

Nickel-based electrocatalysts are identified as the promising candidates for both urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) in urea-assisted water electrolysis to accelerate energy saving hydrogen production. However, the high occupation of Ni 3d orbital leads to their constrained adsorption for reactant and multiple intermediates during UOR process. Herein, considering the d-band electron complementation, the bimetallic MoNi4 hollow nanocubes self-assembled with numerous ultrathin nanosheets was constructed by introducing molybdenum with relatively empty d orbital and synergistically boost UOR/HER activities. Notably, the MoNi4 requires a lower cell voltage of 1.462 V to drive a current density of 10 mA cm−2 in urea electrolyzer, superior to that in water electrolyzer (1.796 V) and most of the reported nickel-based electrocatalysts, as well as the urea degradation rate is impressive. In situ technologies including electrochemical impedance spectroscopies and Raman spectra reveal that the favorable UOR pathway can be initiated directly by the reconstructed NiOOH species. Density functional theory (DFT) calculations prove that the urea molecular are preferential absorbed on Ni site and then collaborate with the adjacent Mo site to carry out the subsequently dehydrogenation, N-N coupling, and desorption in energetically favorable pathways, proving their dual site mechanism (synergy between Mo and Ni).

Formulasi dan Evaluasi Tablet Urea Lepas Lambat Berlapis Biopolimer Poliasam Laktat Sebagai Suplemen Ruminansia

Urea is a source of non-protein nitrogen (NPN) which can be used to replace pure protein in ruminants. Urea is easily soluble and is degraded to ammonia by rumen bacteria, thus affecting the quality of ruminants. To increase the utilization of urea as a supplement is to try to slow its release into ammonia in the rumen so that it can be used efficiently by rumen microbes to form microbial protein. Slow release urea tablets as an alternative can control the rate of urea degradation and release of ammonia into the rumen and increase rumen efficiency. This study aims to determine the rate and pattern of release of urea tablets in the rumen so that their use is more practical and the dosage is correct. To maintain ammonia levels in the rumen, an alternative polymer-coated urea slow release tablet was designed. Based on this, it was carried out to manufacture slow release urea tablets with biopolymer polylactic acid (PLA) coating in the rumen fluid of ruminants. Furthermore, an in vitro evaluation was carried out by measuring pH into rumen fluid and measuring NH3 by UV-Vis spectro analysis at a wavelength of 630 nm. The results of the test for urea release in the rumen in formulas 1, 2 and 3 were 75.133%, 76.076% and 74.051% respectively, while the release of urea in uncoated urea tablets was 96.384%, these results indicate that tablets with lactic acid coated polyacid last longer. release compared to urea tablets without biopolymer coating.

Metal-Organic Frameworks Offering Tunable Binary Active Sites toward Highly Efficient Urea Oxidation Electrolysis.

Electrocatalytic urea oxidation reaction (UOR) is regarded as an effective yet challenging approach for the degradation of urea in wastewater into harmless N2 and CO2. To overcome the sluggish kinetics, catalytically active sites should be rationally designed to maneuver the multiple key steps of intermediate adsorption and desorption. Herein, we demonstrate that metal-organic frameworks (MOFs) can provide an ideal platform for tailoring binary active sites to facilitate the rate-determining steps, achieving remarkable electrocatalytic activity toward UOR. Specifically, the MOF (namely, NiMn0.14-BDC) based on Ni/Mn sites and terephthalic acid (BDC) ligands exhibits a low voltage of 1.317 V to deliver a current density of 10 mA cm−2. As a result, a high turnover frequency (TOF) of 0.15 s−1 is achieved at a voltage of 1.4 V, which enables a urea degradation rate of 81.87% in 0.33 M urea solution. The combination of experimental characterization with theoretical calculation reveals that the Ni and Mn sites play synergistic roles in maneuvering the evolution of urea molecules and key reaction intermediates during the UOR, while the binary Ni/Mn sites in MOF offer the tunability for electronic structure and d-band center impacting on the intermediate evolution. This work provides important insights into active site design by leveraging MOF platform and represents a solid step toward highly efficient UOR with MOF-based electrocatalysts.

Combined aerobic resistance exercise improves dialysis adequacy and quality of life in patients on maintenance hemodialysis .

This study aims to compare the effect of pure aerobic exercise and combined aerobic resistance exercise on dialysis adequacy and quality of life in patients on maintenance hemodialysis. A total of 45 patients on maintenance hemodialysis were divided into three groups: pure aerobic exercise group, combined aerobic resistance exercise group, and control group. Patients in the control group were only given the usual treatment, which included dietary guidance, drug therapy, and hemodialysis. The other training groups underwent 12-week exercise intervention therapy on the basis of the usual treatment. Blood samples were collected before and after the hemodialysis, at the beginning and end of the intervention for these three groups. Then, the blood urea nitrogen (BUN) concentration was determined, the urea clearance index (Kt/v) and urea degradation rate (URR) were calculated, the dialysis adequacy was evaluated, and the short form-36 (SF-36) scale was used to evaluate the life quality. Before intervention, there was no significant difference in general health condition (GH), Kt/v, URR, SF-36 total score, and the score of each dimension in the three groups. After the intervention therapy, the Kt/v, URR, GH, vitality (VT), and SF-36 total score markedly improved in the pure aerobic exercise group, while the Kt/v, URR, GH, VT, physical functioning (PF), and SF-36 total score significantly increased in the combined aerobic resistance exercise group. Furthermore, compared with the pure aerobic exercise group, the improvement effect of body function (PF score) was better in the combined aerobic resistance exercise group. Both pure aerobic exercise and combined aerobic resistance exercise can significantly improve the dialysis adequacy and quality of life of maintenance hemodialysis patients. Compared with the pure aerobic exercise group, the effect of combined aerobic resistance exercise on PF was better. .

In Situ Growth of Highly Active MgAl Layered Double Hydroxide on η-Al2O3 for Catalytic Hydrolysis of Urea in Wastewater

Magnesium aluminum layered double hydroxide (MgAl–LDH) was first successfully deposited in situ on η-Al2O3 applied to catalyze urea hydrolysis. Characterization by AAS, XRD, SEM, EDS, DSC, FT-IR, N2-BET, determination of base strength and basicity and experiments on hydrolysis activities of in situ MgAl–LDH catalysts show that the crystallinity and coverage degree of MgAl–LDH on η-Al2O3 gradually increase with increasing initial c(Mg2+). When initial c(Mg2+) = 2 mol L−1, η-Al2O3 is completely covered and the smallest particle size, the highest crystallinity, basicity and urea degradation rate of in situ MgAl–LDH are obtained. The basicity is mainly from Mg–OH at the edges of MgAl–LDH on η-Al2O3. The highest basicity corresponds to the highest urea degradation rate, Mg–OH is the active sites for catalytic hydrolysis of urea. The specific surface area, basicity and catalytic activity of MgAl–LDH by in situ synthesis are evidently higher than MgO and MgAl–LDH purchased. The urea concentration is 8.162 mg L−1 at 165 °C after 120 min with in situ MgAl–LDH (c(Mg2+) = 2 mol L−1) as catalyst, which is below the effluent standard. In situ MgAl–LDH also shows excellent recycling ability and the slight loss of activity should be due to the reduction of basicity, which is caused by hydrothermal conditions. In addition, a possible catalytic mechanism of urea hydrolysis over MgAl–LDH is proposed.

Biochemical process of ureolysis-based microbial CaCO3 precipitation and its application in self-healing concrete.

Urea hydrolysis has already been considered as the most effective pathway for microbially induced CaCO3 precipitation (MICP). The present work first studied the combination of several key factors including initial pH, temperature, and dosage of urea, which contribute to the biochemical process of MICP. Under an amiable condition of pH and temperature, the dosage of urea has a significant impact on the rate of urea degradation and CaCO3 precipitation. A bacteria-based self-healing system was developed by loading healing agents on ceramsite carriers. The self-healing efficiency was evaluated by visual inspection on crack closure, compressive strength regain, and capillary water absorption. A preferable healing effectiveness was obtained when the bacteria and organic nutrients were co-immobilized in carriers. Image analysis showed that cracks up to 273μm could be healed with a crack closure ratio of 86% in 28days. The compressive strength regain increased 24% and the water absorption coefficient decreased 27% compared to the reference. The findings indicated a promising application of ureolysis-based MICP in restoring the mechanical properties and enhancing the durability of concrete.

Biogeochemical cycling of urea in the aquatic systems of Pindaré and Turiaçu River basins, a pre-Amazonian floodplain, Baixada Maranhense, Brazil

AIM: This work is aimed at extending the understanding of urea cycle in freshwater ecosystems. Its degradation rate concerning microorganisms activities was measured in the turbid waters of Pindaré and Turiaçu rivers located on the pre-Amazonian floodplain, Brazil; METHODS: The Pindaré and Turiaçu aquatic systems have distinct dry and rainy periods. The investigation was developed in the middle of the rainy period, and field activities were carried out in the extensive water bodies from the middle to lower reaches. The rate of degradation in the surface waters of the two aquatic systems was determined with in situ simulation technique using 14C-labelled urea. Photosynthetic rates were determined by the radiocarbon technique simultaneously with experimental measurements of urea degradation rate; RESULTS: Urea degradation rates (sum of carbon incorporation into particulate matter and CO2 liberation into water) were 2.0 mg urea C m-3 day-1 in the Pindaré and 17.1 mg urea C m-3 day-1 in the Turiaçu waters. Daylight values were obviously higher than those in the dark, and the urea degradation rates in Turiaçu showed much higher values than those in Pindaré. Most of the urea degradation occurred during the CO2 liberation phase. The average of chlorophyll a specific urea degradation rate was 0.13 and 0.83 mg urea C mg chl.a-1 day-1 in both river waters. The ratio of urea carbon degradation to photosynthetic carbon assimilation in both waters averaged 1.2 and 4.2%, respectively. The residence time of urea in the surface water was calculated as 2.3 to 4.5 days in the Pindaré and 0.21 to 0.50 days in the Turiaçu. Much shorter residence times were obtained in the Turiaçu due to the high degradation rate of urea; CONCLUSION: The correlation coefficient between the urea degradation rate and chlorophyll a or photosynthetic rate showed a statistically significant value in the Turiaçu. This indicates that in the Turiaçu system the urea degradation rate was proportional to the standing crop of phytoplankton and their photosynthetic rate. A strong relationship between the urea carbon incorporation rate and photosynthetic rate in the light bottles was observed, indicating that the carbon incorporation into the phytoplankton cells was also related to the photosynthetic rate. The present brief residence time indicates that the urea was being rapidly recycled in the euphotic zone of the investigated systems in the rainy period.

Assessment of Urea Degradation Rate in Model Wine Solutions by Acid Urease fromLactobacillus fermentum

The specific activity (piA) of a whole cell acid urease preparation was assessed in model wine solutions at different levels of malic (M) and lactic acids, metabisulfite, ethanol, and pH by performing a central composite design. M and then pH were found to be the most controlling variables, their effects being practically coincident but of opposite sign. For urea concentrations up to approximately 1 mol m(-3) the ammonium formation rate was assumed of the pseudo-first-order with respect to urea, this being confirmed by two independent validation tests performed at 20 degrees C for as long as 24 h. In the case of real wines the effective pseudo-first-order kinetic rate constants were found to be smaller than those pertaining to the model solutions having the same wine composition and pH by a factor varying from 10 to 1000, this affecting significantly the specific urease treatment costs per liter of wine treated.

KINETICS OF UREA DEGRADATION BY GENETICALLY MODIFIED E. COLI

Malchesky first reported the degradation of urea by wild type cells grown in media containing an uremic molecule (Trans Am Soc Artif Int Organs 7977 23:726). Chang subsequently described the metabolism of urea by E. Coli cells modified to contain the gene for urease and proposed a therapy format based upon oral ingestion of encapsulated cells (Nat. Med. 1996 2:883). In order to further develop this intriguing technology, we have begun to characterize the kinetics and mechanism of bacterial urea degradation. All studies were conducted with E. Coli DH 5 cells (kindly provided by S. Mulrooney, Mich. State U.) containing the urease plasmid pkAU17 from Klebsiella aerogens along with an ampicillin resistant gene. Cells were passaged in Luria-Bertani (LB) media containing urea and ampicillin. The rate of urea degradation from a 100 mg/dl starting concentration of urea varied in dose dependent fashion on the concentration of modified cells in a challenge solution. Small aliquots of these cells in LB media grew to a concentration of −1 million cells/ml in 48 hours. At this concentration, cells were found to completely degrade urea at a starting concentration of 100 mg/dl in less than one hour. Supernatant from cultures of modified cells had no capacity to degrade urea, suggesting that the degradation process is intracellular. The mass efficiency of urea degradation by genetically modified cells (approximately three mg urea removed per μg of cells per hour) was greater than that of constructs prepared from purified urease suspended in alginate and appeared adequate for therapeutic consideration. In our expereincee at least, it was not possible to condition unmodified control E. Coli cells to degrade urea by prolonged passaging in urea-containing culture media.

酸性ウレアービによる尿素分解速度の欧州産と米国産ワインにおける比較及びワイン成分との関係

The rate of urea degradation by acid urease in European and American wines were compared and it was shown that the average degradation rate in European wine was 6-9 fold higher than that of American wine, in both white and rose wine. Consequently, urea reduction by urease treatment is more difficult in American wine than in European wine. There was little difference in the urea degradation rates for red wine. A significant negative correlation was observed between fluoride concentration and the degradation rate, in addition, a significant difference in fluoride concentration was found in European and American white/rose wines. Therefore, it was suggested that the high concentration of fluoride in American wine made urea reduction difficult. A significant positive correlation was found between Llactate concentration and the degradation rate.

Urea degradation by picophytoplankton in the euphotic zone of Lake Biwa

The ability of photoautotrophic picoplankton Synechococcus to degrade urea was examined in the euphotic zone of Lake Biwa. Samples were divided into pico (0.2–2.0 μm) and larger (>2.0 μm) size fractions by filtration. The rates of urea degradation (the sum of the rates of incorporation of carbon into phytoplankton cells and of liberation of CO2 into water) measured by radiocarbon urea were 8 and 17 μmol urea m−3 day−1 in June and July, respectively, for the picophytoplankton in the surface water, and 196 and 96 μmol urea m−3 day−1, respectively for the larger phytoplankton. The rates decreased with depth, somewhat similar to the vertical profiles of the photosynthetic rate. The urea degradation rates were obviously high under light conditions. In daylight, urea was degraded into two phases, carbon incorporation and CO2 liberation, whereas in the dark it was degraded only into the CO2 liberation phase. The contribution of picophytoplankton to total phytoplankton in urea degradation was high in the subsurface to lower euphotic layer. Urea degradation activity was higher in the picophytoplankton fraction than in the larger phytoplankton fraction. Shorter residence times of urea were obtained in the upper euphotic zone. The contribution of picophytoplankton to urea cycling was 4% to 35%. The present results suggest that the picophytoplankton Synechococcus is able to degrade urea and effectively makes use of regenerated urea as a nitrogen source in the euphotic layer, and that picophytoplankton play an important role in the biogeochemical nitrogen cycle in Lake Biwa.

Influence of the novel urease inhibitor N-(n-butyl) thiophosphoric triamide on ruminant nitrogen metabolism: I. In vitro urea kinetics and substrate digestion.

Two in vitro digestion experiments were conducted to evaluate the influence of the novel urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) on in vitro urea kinetics, substrate digestion, and fermentation characteristics. In Exp. 1, in vitro incubations were conducted in 50-mL test tubes containing .25 g of ground fescue hay to which 0, 6.5, 13, 26, or 52 mg of NBPT in a buffered ruminal fluid innoculum was added. Tubes were incubated in triplicate at 39 degrees C and replicated on consecutive days, with NH3 N and urea concentrations measured at 0, 10, 30, 60, 120, 240, and 360 min. Samples for VFA analysis were collected at 6 h, and incubations were continued through 48 h to estimate true digestibility (based on NDF analysis). Increasing the dose of NBPT tended (P < .12) to linearly depress the rate of urea hydrolysis and decreased (P < .0004) subsequent NH3 N formation. Although total VFA concentration at 6 h increased linearly (P < .03), acetate:propionate and estimated true digestibility decreased (P < .01) with increasing NBPT concentration. In Exp. 2, we compared in vitro urea kinetics and digestion of forage-only or mixed forage-grain substrates in response to addition of NBPT. In vitro incubations were conducted in 50-mL test tubes containing either .5 g of ground fescue hay or .5 g of a ground fescue hay and ground corn mixture (50:50, DM basis) to which 0, 6.5, 13, 26, or 52 mg of NBPT in a buffered ruminal fluid innoculum was added. Tubes were incubated in triplicate at 39 degrees C and replicated on consecutive days, with NH3 N and urea concentrations measured at 0, .5, 1, 2, 4, 8, 12, 24, and 48 h. At 48 h, samples for VFA analysis were collected and true digestibility (based on NDF analysis) was estimated. No (P > .10) NBPT dose x substrate interactions were detected. Increasing the dose of NBPT depressed (P < .003) the rate of urea hydrolysis and subsequent NH3 N formation, regardless of substrate. Although total VFA concentration was unaffected (P > .10), the acetate:propionate and estimated true digestibility decreased (P < .002) with higher NBPT addition. In both experiments, the rate of urea degradation was not different (P > .20) from zero for the 26 and 52 mg NBPT treatments, indicating that nearly complete inhibition of urease had been achieved. We conclude that NBPT can be used to reduce the rate of NH3 N release from dietary urea and, thereby, offers the potential to improve nonprotein nitrogen utilization in ruminants.

Suppression of Helicobacter pylori urease activity by sucralfate and sulglycotide.

The effect of gastroprotective agents, sucralfate and sulglycotide, on the in vitro activity of H. pylori urease was investigated. The bacterium was subjected to sonication, centrifuged, and the supernatant used as an enzyme source. The assays revealed that the rate of urea degradation was proportional to enzyme protein up to 100 micrograms and remained constant with time for 10 min. Introduction of sucralfate or sulglycotide to the assay system led to the reduction in the rate of ammonia production. With both drugs the optimal inhibition was attained at 10 micrograms/ml, at which dose a 63.1% decrease in urease activity occurred with sucralfate and a 70.2% inhibition was obtained with sulglycotide. The findings demonstrate that the inhibitory action of sucralfate and sulglycotide on H. pylori urease activity may be of value in the treatment of gastric disease associated with H. pylori infection.

Effects of intraruminal infusions of urea, sucrose or urea plus sucrose on plasma urea and glucose kinetics in sheep fed chopped lucerne hay

SUMMARYThe effect of rumen fermentation on the relationship between urea and glucose kinetics was examined in sheep fed chopped lucerne hay with intraruminal infusions of water, urea, sucrose, or urea plus sucrose at Palmerston North, New Zealand in 1986. Sheep were fed hourly and infused intraruminally with water (1200 m1/day), or a similar volume containing either urea alone (13·7g/day), sucrose alone (178·2 g/day) or urea (14·6 g/day) plus sucrose (175·0 g/day). The added sucrose resulted in a lower rumen ammonia concentration (P&lt; 0·05), lower plasma urea concentration (P&lt; 0·05) and reduced urinary urea excretion (P&lt; 0·05). Urea recycled to the gut tended to increase with the sucrose, urea or sucrose plus urea treatments compared with the water treatment. The fermentation of sucrose in the rumen resulted in decreases in ruminal pH (P&lt; 0·05) and in the ratio of acetate to propionate (A:P) (P&lt; 0·05). The infusion of sucrose also increased the concentration of propionate in rumen fluid (P&lt; 0·05), tended to increase the plasma glucose level and increased plasma glucose irreversible loss (P&lt; 0·05). The infusion of urea resulted in an increase in the plasma urea level (P&lt; 0·05), urea pool size (P&lt; 0·05) and urea irreversible loss (P&lt; 0·01). However, urea infusion did not affect glucose metabolism or volatile fatty acid (VFA) fermentation. The effects of sucrose infusion on glucose and urea kinetics were broadly similar when given alone or with urea, apart from changes in the urea degradation rate. It was concluded that the additional fermentative activity resulting from sucrose increased propionate production which, in turn, was available for glucose production, thus ‘sparing’ amino acids for tissue protein utilization and reducing urea excretion.

Tracer studies of urea kinetics in growing pigs: I. The effect of intravenous infusion of urea on urea recycling and the site of urea secretion into the gastrointestinal tract

Four gilts (average BW 80 kg) were used in the first experiment to study the effect of i.v. infusion of urea on urea kinetics by means of a radioisotope dilution technique. The pigs were fed twice daily 600 g of a cornstarch-based diet formulated to contain 16% CP by supplementation with isolated soy protein. Infusion of urea, compared with saline, increased (P < .05) plasma urea concentration, urea pool size, urea entry, urea excretion, and urea degradation rates; urea turnover rate and urea space were not affected (P > .05). Expressed as a percentage of the total entry rate, a lower (P < .05) percentage of urea was recycled in pigs infused with urea. The urea infused was almost completely excreted in urine, so there were no differences (P > .05) in N balance. In the second experiment, four gilts (average BW 40 kg), fitted with ileocecal reentrant cannulas, were used to determine whether the upper or the lower digestive tract represents the preferential site of urea secretion in pigs. Two pigs were fed twice daily 600 g of a cornstarch-based diet, formulated to contain 16% CP from soybean meal. The other two pigs were fed the same diet in which 15% cornstarch was replaced by beet pulp. After labeling the body urea pool of one pig on each treatment with [15N]urea, the reentrant cannulas were disconnected to prevent the flow of digesta from the small into the large intestine.(ABSTRACT TRUNCATED AT 250 WORDS)

Urea degradation rates by size-fractionated plankton populations in a temperate estuary

The distribution of the rates of remineralisation and assimilation of labelled urea by bacteria was determined in a temperate estuary in winter and related to the activities of planktonic populations separated by filtration into a large fraction (LF > 3 μm) and small fractions (SF < 3 μm). A significant relationship was established between remineralisation activity of the SF in situ and the ambient urea concentrations, whereas corresponding relationships between the LF in situ and urea concentrations were inconsistent. A series of comparable artificial dilution experiments demonstrated consistent effects of salinity on rates of urea remineralisation with opposing relationships observed for the LF and SF. However interpretation of the data obtained from the in situ samples in relation to those obtained experimentally indicated only minimal control of the in situ rates of urea remineralisation by salinity, thus confirming the greater influence on these rates of the ambient urea concentrations. Remineralisation activity was approximately an order of magnitude greater than the assimilation activity with no clear trends being shown between assimilation rates and environmental variables. Highest ambient concentrations of urea were consistently recorded adjacent to the freshwater inflow.

87:6458 Urea degradation rates by size-fractionated plankton populations in a temperate estuary: Savidge, G. and J.P. Johnston, 1987. Estuar. coast. Shelf Sci., 24(4):433–447. Mar. Biol. Station, Portaffery, Co. Down, BT22 1PF, Northern Ireland

87:6458 Urea degradation rates by size-fractionated plankton populations in a temperate estuary: Savidge, G. and J.P. Johnston, 1987. Estuar. coast. Shelf Sci., 24(4):433–447. Mar. Biol. Station, Portaffery, Co. Down, BT22 1PF, Northern Ireland

Urea turnover and transfer to the digestive tract in the rabbit.

14C and 15N isotopes of urea were infused intravenously into rabbits for 6-8 h in order to measure urea synthesis and the extent of degradation in the digestive tract. The results indicate that 0.62 of the urea flux was excreted in the urine and that re-incorporation of urea-N following hydrolysis in the gut represented 0.3 of the urea synthesis rate. Sampling of metabolites from the caecum by dialysis provided an opportunity to assess the contribution of urea-N to the caecal ammonia pool. This contribution is calculated to be 0.25 of caecal ammonia turnover. Infusion of a urease (EC 3.5.1.5) inhibitor during a continuous infusion of [14C]urea into the caecum permitted the measurement of urea turnover within the caecum. Results obtained for urea entry into the caecum are contrasted with the measured urea degradation rate in the gut.

Effects of lactulose and neomycin on urea metabolism in cirrhotic subjects

In our previous studies of cirrhotic subjects lactulose caused a 25% decrease in the urea production rate associated with a decrease in urinary urea excretion and an increase in stool nitrogen. The decrease in the rate of urea production was an indirect measure of reduction in gut ammonia production. The present study was designed to determine if the poorly absorbed antibiotic neomycin had an additive effect in reducing ammonia production when administered in combination with lactulose. Six stable cirrhotic subjects received isonitrogenous diets during separate lactulose and lactulose + neomycin treatment periods. The addition of neomycin to a lactulose regimen caused a 17% reduction in the urea production rate that was quantitatively accounted for by a 70% reduction in the urea degradation rate. The intestinal urea clearance rate demonstrated a parallel reduction, indicating an inhibition of bacterial ureolysis. There was no evidence that neomycin altered the effects of lactulose since urinary urea excretion did not rise, fecal nitrogen remained high, and stools remained acidic. These results demonstrate that neomycin inhibited bacterial ureolysis when administered with lactulose while lactulose itself was metabolized and its individual effect on nitrogen metabolism persisted. Lactulose and neomycin, when administered together, had an additive effect in reducing gut ammonia production in cirrhotic subjects.

Studies on the Nutrition of Macropodine Marsupials. 2. Urea and Water Metabolism in Thylogale Thetis and Macropus Eugenii; Two Wallabies From Divergent Habitats.

Urea and water metabolism were studied in the red-necked pademelon Thylogale thetis. and tammar wallaby Mucropus eugenii fed diets of chopped lucerne hay and fresh grass Phalaris aquatica ad libitum. On both diets T. thetis consumed more nitrogen (P&lt;0.05), plasma urea levels were higher (P&lt;0.05) and urea entry rate was greater (P&lt;0.05) than in M. eugenii. Urea excretion rate was greater (P&lt;0.05) in T. thetis than in M. eugenii on the lucerne diet, and urea degradation rate was greater (P&lt;0.05) in T. thetis on the Phalaris diet. The proportion of urea synthesized that was recycled to and degraded in the digestive tract was similar (52-56%) in both species on both diets. T. thetis consumed more water (feed and drinking water) (P&lt;0.05), and water turnover time was less (P&lt;0.05) and turnover rate greater (P&lt;0.05) than in M. eugenii, on both diets. At least on diets of adequate nitrogen and digestible energy content, it appears that differences in nitrogen metabolism between T. thetis and M. eugenii are not attributable to differences in gut microbial activity; rather, the results of this and other studies suggest that M. eugenii has a greater urine-concentrating ability and lower maintenance requirements than T. thetis.