Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “UREA”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources
PubMed1994

Urea kinetic modeling at high urea clearances: implications for clinical practice.

The original description of urea kinetic modeling in hemodialysis was based on a single pool of fluid equal to total body water. This assumption is valid only if the rate of transport between compartments is sufficiently rapid compared with the rate of urea removed by hemodialysis. We have reexamined the issue of urea compartmentation using 10 patients with initial BUN values ranging from 28 to 101 mg/dL who were studied while on high flux hemodiafiltration. Sampling was carried out at times as short as 1 minute after the beginning of the treatment. In 4 patients, samples were also drawn after the dialysis ended. The measured BUN values were used to fit a two-compartment, variable-volume kinetic model. The mean urea diffusive clearance of the dialyzer during the treatment was 503 mL/minute, and the bidirectional urea clearance between compartments was 1,282 mL/minute. The percentage of total body water in the rapidly exchangeable compartment was 35.4%. Comparison with a one-compartment, variable-volume model showed a statistically better fit for all patients with the more complex model. In the 4 patients studied in the postdialysis period, the rebound in BUN ranged from 22% to 24%. These studies show that, at high urea clearances, the urea distribution space and, therefore, dialysis modeling requires two compartments. These results explain the majority of the rebound in urea concentration observed 30 to 60 minutes following the discontinuation of the dialysis treatment and point out an improved strategy for monitoring the efficiency of the treatment delivered to the patient.

Blood Urea Nitrogen↗
PubMed1994

Why do some organisms use a urea-methylamine mixture as osmolyte? Thermodynamic compensation of urea and trimethylamine N-oxide interactions with protein.

Many organisms accumulate low molecular weight substances known as osmolytes when they experience environmental water stress. The main classes of osmolytes are sugars, polyhydric alcohols, amino acids and their derivatives, and methylamines, and all are known to be protein stabilizers. However, marine cartilaginous fishes and the coelacanth use, as osmolytes, a combination of urea and methylamines, i.e., a denaturant and a stabilizer, in a 2:1 molar ratio. Preferential binding and thermal denaturation measurements in the presence of each cosolvent separately and in their mixtures have been carried out using ribonuclease T1 (RNase T1) as the protein. At a 2:1 molar ratio of urea and trimethylamine N-oxide (TMAO), the effects of the two cosolvents on the transition temperature (Tm) were found to be essentially the algebraic sum of their effects when used individually. Preferential interaction measurements of urea, TMAO and urea in its 2:1 molar ratio mixture with TMAO, have shown that the presence of TMAO has no effect on the interaction of urea with the protein in either the native or the unfolded (reduced carboxymethylated RNase T1) state. The preferential interaction of TMAO in the presence of urea could not be measured for technical reasons. Calculations of transfer free energy in the two end states of the denaturation reaction have shown that 2 M urea destabilizes RNase T1 by 3.8 +/- 0.3 kcal/mol whether 1 M TMAO is present or not. The contribution of 1 M TMAO to stabilization is calculated to be 3.1 kcal/mol in the presence of 2 M urea and is measured to be 2.7 kcal/mol in its absence.

Methylamines↗
PubMedDate not supplied

The effects of sodium chloride, urea and mannitol on the permeability in vitro fo rat papillary collecting ducts to THO, 14C-urea and 22Na.

1. The diffusional permeabilities of collecting duct membranes to THO, 14C-urea and 22Na+ have been measured at different concentrations of urea, NaCl and mannitol. 2. In the absence of urea in perfusate and bath or in its presence in low concentrations, the diffusional permeability to urea was 2.0 (s.e.m. = 0.15, n = 58) micrometer s-1, compared with 0.87 (s.e.m. = 0.06, n = 29) microgram s-1 when 200 mmol/l urea was present. The permeability of the collecting ducts to THO or Na+ was not affected by the different urea concentrations. 3. High concentrations of sodium chloride increased the diffusional permeability of collecting ducts to water and urea but did not affect the diffusional permeability of the collecting duct to Na+. 4. Mannitol had effects similar to those of sodium chloride. 5. In all media tested there was an increase in THO and urea permeability when supramaximal amounts of antidiuretic hormone were added. The increases in the various media for each substance were similar, despite widely different starting permeabilities. 6. The results suggest that solutes and water move across collecting duct epithelium by several pathways that respond differently to various stimuli.

Animals↗
PubMed1999

Comparison of [13C]urea blood test to [13C]urea breath test for the diagnosis of Helicobacter pylori.

OBJECTIVE: It has been determined that the [13C]urea breath test (UBT) is a safe and effective way of detecting Helicobacter pylori (H. pylori) infection. Some individuals may have difficulty performing the exhalation component of the test, possibly due to age, or mental or physical compromise. Our aim was to determine if a commercially developed [13C]urea blood test could be utilized as a substitute for the UBT to detect H. pylori infection. METHODS: Patients who were referred by their physicians for UBT were offered study inclusion. Patients underwent baseline and 30-min UBT. A simultaneous blood sample of 3 cc was drawn into a heparinized vacutainer at the 30-min period of the UBT. [13C]urea levels in both blood and breath samples were analyzed using isotope ratio mass spectrometry. UBT > or = 6 delta per mil over baseline and urea blood tests > (-17 delta per mil) were considered positive. RESULTS: One hundred sixty-one patients (68 men/93 women) with average age of 47.0 +/- 14.2 yr were tested. Agreement between breath and blood test results occurred in 153/161 (95%) cases. Using the UBT as the diagnostic standard, the urea blood test resulted in 44 true positive, 109 true negative, four false positive, and four false negative results, giving a sensitivity of 92%, specificity of 96%, positive predictive value of 92%, and negative predictive value of 96%. CONCLUSIONS: The urea blood test was found to be comparable to the urea breath test in the detection of H. pylori infection. The urea blood test will be accurate in the diagnosis of active H. pylori infection.

Breath Tests↗
PubMed1986

[The protein-synthesizing function of the liver in dairy cows fed feed with the addition of various urea preparations and different doses of urea].

It was compared the effect of different preparations containing urea on the productivity and on the blood content of the biochemical compounds informing about protein synthesis activity in the liver of milk cows. The following preparations were added alternatively to the food to 28 cows in a quantity equal with 150 Gm in the first year and with 200 Gm of pure urea in the second year of experimentation for cow and for day: 1. Melwit--a liquid food supplementation containing 5 per cent of urea, 2. Wałczan--"Sterea"-like preparation with 30 p.c. of urea, 3. Ekstruder--"Golden-Pro"-like preparation with 20 p.c. of urea and 4. BW preparation (concentration) for dairy cows containing only plant protein, without urea. In the plasma of all animals was observed the increase of urea, total protein and albumin content and of the activity of following enzymes: AP, AAP, Arg, LAP, AspAT and of A1AT. The content of total and of direct bilirubin in plasma did not change significantly. All examined compounds did not exceed the physiological range. The greatest changes were observed after feeding with Extruder. The physiological decline of milk production after calving was smallest in group fed with Wałczan (2.4 litres) and greatest in Ekstruder group (4.4 litres) when in Melwit 3.4 and in BW 3.5 litres was noticed. The authors stated that the most suitable form of preparation containing urea was Wałczan in the first place and Melwit in the second.

Animal Feed↗
PubMed1995

Denaturation of pteroylpoly-gamma-glutamyl hydrolase from chicken liver by urea, thiourea and guanidine hydrochloride: altered catalytic properties of the enzyme activated by urea.

The effects of varying concentrations of urea, thiourea and guanidine hydrochloride on the enzyme activity and the isoenzymic polypeptide association of pteroylpoly-gamma-glutamyl hydrolase (EC 3.4.22.12) from chicken liver were studied. Incubation of the enzyme at 4 degrees C with low concentrations of the buffered (100 mM sodium acetate containing 1% ascorbate, pH 4.1) solutions of urea (0.55 M) and guanidine hydrochloride (0.05 M) resulted in stimulation (5- and 2-fold respectively) of the activity of the enzyme whereas at higher concentrations of the denaturants (6 M urea, 1 M thiourea or 2 M guanidine hydrochloride) the enzyme was completely inactivated. However, there was no enzyme activation in response to thiorea treatment. Under specific denaturing conditions the association of two isoenzymic polypeptides was studied. The 0.55 M urea- and 0.05 M guanidine hydrochloride-activated enzyme displayed its disaggregated nonidentical polypeptides I and II (M(r) = 41,000 and 17,300 respectively) on Sephadex G-100 gel filtration, SDS-PAGE and sedimentation analyses. The 8 M urea- and 3 M guanidine hydrochloride-inactivated enzyme on the other hand exhibited a single protein aggregate species of an M(r), 57,000 like the native enzyme. Both unmodified native enzyme and the pCMB-modified PtepolyGlu hydrolase responded similarly to these denaturants. The two constituent active polypeptides polyp-I and polyp-II of the heterodimeric gamma-glutamyl glutamyl hydrolase are dissociated in the presence of 0.55 M urea as evident from the PAGE analyses. Some catalytic properties of the activated enzyme were studied and compared with those of the native enzyme. The urea-activated enzyme displayed a shift in the second pH optimum of the double pH-activity profile (optima at pH 4.1 and pH 5.2) from pH 5.2 to pH 6.0. The activated enzyme has a Km value of 0.59 x 10(-6) M (Vmax, 0.10) for 5-CH3-H4PteGlu4 while the native enzyme has the Km of 0.83 x 10(-6) M (Vmax, 0.03) for this substrate. When the reaction mixtures were incubated with the urea-activated gamma-glutamyl hydrolase, a maximum stimulatory effect on the enzyme activity was observed with the bivalent metal ion Ca2+ whereas the most potent inhibitory effect was observed with the trivalent anion citrate.

Animals↗
PubMedDate not supplied

Urea kinetic modeling with a prototype urea sensor in the spent dialysate stream.

The authors have previously demonstrated the feasibility and accuracy of urea kinetic modeling (UKM) based on monitoring urea concentration in the spent dialysate stream (SDS) throughout the hemodialysis (HD) session. They describe here a prototype urea sensor for this purpose and initial experience with HD patients. The sensor is based on ammonium ion and reference electrodes housed in a cell through which the entire SDS passes. The two electrode tips are bathed in urease solution on one side of a dialysis membrane; the SDS flows along the adjacent side. Urea diffusing across the membrane from the SDS is converted by the urease into ammonium ion, which is measured by the electrode pair. For evaluation, the prototype flowthrough urea sensor was installed in the SDS of a Cobe Centry 3 HD machine for 36 HD sessions. Independent measurement demonstrated a linear relationship between mv output of the sensor and logarithm of SDS urea concentration. The use of SDS urea concentration time profiles obtained with this sensor to obtain accurate values of patient protein catabolic rate (PCR) and KT/V is illustrated. Incorporation of urea sensors such as this prototype into HD machines, will permit complete automation of UKM in the near future.

Dialysis Solutions↗
PubMed1995

Urea kinetics: effect of severely restricted dietary intakes on urea hydrolysis.

Urea kinetics (urea-N production-P, excretion-E, hydrolysis-H, recycling-R and retention-S) were measured in 7 healthy adults consuming a standard diet compared with 4 fasted for 24 and/or 96 h, using primed/intermittent doses of [(15)N (15)N]-urea and mass spectrometry. Standard values were P = 196, E = 132, H = 65, R = 13 and S = 51, mgN/kg/day. After 24 h fasting all urea kinetics were reduced, and P and H were significantly reduced compared with the standard diet (p < 0.01 and < 0.05 respectively). After 96 h fasting, urea kinetics returned to standard values (P = 187, E = 136, H = 51, R =13 and S = 38, mgN/kg/day), although nitrogen intake was significantly lower (p < 0.001). Relative urea excretion (E/P) was 67%, standard diet, and 75% after fasting. Consequently H/P was slightly reduced from 33 to 25%. S/P was 26%, standard diet, 15% after 24 h and 20% after 96 h fasting, suggesting increased urea-N retention with prolonged fasting. These results imply a slight temporary shift towards increased nitrogen excretion at 24 h and subsequent return to the kinetics of the fed state after 96 h. Urea-N retention increases with prolonged fasting.

Journal Article↗
PubMed2005

Impaired urea accumulation in the inner medulla of mice lacking the urea transporter UT-A2.

Urea transporter UT-A2, the major urea transporter of the thin descending limb of the loop of Henle in short loop nephrons, has been implicated in urea recycling in the medulla, thereby producing concentrated urine. To investigate the physiological role of UT-A2 in vivo, we generated UT-A2-selective knockout mice by deleting the UT-A2 promoter. Western analysis, immunohistochemistry, and quantitative reverse transcription-PCR were used to confirm the specific deletion of UT-A2 with preservation of other UT-A transporters. Compared to wild-type mice, differences in the urine outputs of UT-A2(-/-) mice consuming a normal protein diet (20% protein) were not observed under normal conditions or with dehydration. Likewise, impairment of urea accumulation in the inner medulla of UT-A2(-/-) mice was not observed. On a low-protein diet (4% protein), however, significantly reduced maximal urine osmolality was observed in dehydrated UT-A2(-/-) mice compared to wild-type littermates (2,500 mosmol versus 3,450 mosmol, respectively). A significant reduction in urea accumulation in the inner medulla was also observed in UT-A2(-/-) mice; however, differences in Na(+) and Cl(-) accumulation were not observed. Thus, UT-A2 is important for maintaining a high concentration of urea in the inner medulla when urea supply to the kidney is limited.

Alleles↗
PubMed2006

Non-racemic atropisomeric (thio)ureas as neutral enantioselective anion receptors for amino-acid derivatives: origin of smaller Kass with thiourea than urea derivatives.

The synthesis of a limited series of non-racemic atropisomeric 1-(2-(4-methyl-2-thioxothiazol-3(2H)-yl)phenyl)-3-(hetero)aryl-(thio)ureas is described. Using NMR titration experiments monitoring the shift of the two NH of the (thio)urea and the C-5 hydrogen of the heterocycle, the binding constants for some optically pure (thio)-ureas with the enantiomers of N-protected amino acid tetrabutylammonium salts were determined in CD3CN. The obtained enantioselectivities were modest. Contrary to what was expected on the basis of the NH acidity in thiourea versus urea group, the association constants were smaller with the thiourea than with the corresponding urea. X-ray data, DFT calculations, and NMR provided the explanation of that unexpected behavior: the urea presents a pre-organized (Z,Z) conformation suitable for a double hydrogen bond with the carboxylate anion, the thiourea presents a (Z,E) conformation, which must be reorganized in a constrained (Z,Z) conformation in the complex. An intramolecular hydrogen bond between one NH and the thiocarbonyl group of the heterocycle, which is present in the thiourea and absent in the urea, might also contribute to the smaller K(ass) for the thiourea. The possible implication of these observations in the field of bifunctional organocatalysis is briefly discussed.

Amino Acids↗
PubMed1976

Urea amidolyase of Candida utilis. Characterization of the urea cleavage reactions.

Evidence is presented that the enzymes catalyzing the three reactions involved in urea cleavage in Candida utilis, biotin carboxylation, urea carboxylation, and allophanate hydrolysis occur as a complex of enzymes. The allophanate-hydrolyzing activity could not be separated from the urea-cleaving activity using common methods of protein purification. Further, urea cleavage and allophanate hydrolysis activities are induced coordinately in cells grown on various nitrogen sources. The reactions involved in urea cleavage can be distinguished from one another on the basis of their sensitivities to (a) heat, (b) pH, and (c) chemical inhibitors. Evidence is presented for the product of the first reaction in urea cleavage, biotin carboxylation. Production of carboxylated enzyme is ATP dependent and avidin sensitive. Carboxylated enzyme is not observed in the presence of 1 mM urea.

Acetamides↗
PubMed1993

Effect of dietary protein and urea on in vitro caecal ammonia production from urea and uric acid in cockerels.

1. Single Comb White Leghorn adult cockerels were fed on 50 g/kg protein diet, 200 g/kg protein diet or 50 g/kg protein diet plus urea and in vitro ammoniagenesis from urea and uric acid in the caeca was determined. 2. Four-fold protein intake caused about 4.6-fold increase in caecal ammonia production from urea (P < 0.05), and tended to increase it from uric acid as compared with 50 g/kg protein-fed birds. 3. Dietary urea significantly increased caecal ammonia production from urea and uric acid by about 2 and 3 times as much as those of control birds, respectively (P < 0.05). 4. It is concluded that increased protein intake and the feeding of urea are able to induce ammoniagenesis from urea and uric acid in the caeca of fowls.

Animals↗