Decrease In Urea Concentration Research Articles

Apparent radii of the native, stable intermediates and unfolded conformers of the alpha-subunit of tryptophan synthase from E. coli, a TIM barrel protein.

The urea-induced equilibrium unfolding of the alpha-subunit of tryptophan synthase (alphaTS) from Escherichia coli can be described by a four-state model, N right harpoon over left harpoon I1 right harpoon over left harpoon I2 right harpoon over left harpoon U, involving two highly populated intermediates, I1 and I2 [Gualfetti, P. J., Bilsel, O., and Matthews, C. R. (1999) Protein Sci. 8, 1623-1635]. To extend the physical characterization of these stable forms, the apparent radius was measured by several techniques. Size-exclusion chromatography (SEC), analytical ultracentrifugation (UC), and dynamic light scattering (DLS) experiments yield an apparent Stokes radius, R(s), of approximately 24 A for the native state of alphaTS. The small-angle X-ray scattering (SAXS) experiment yields a radius of gyration, R(g), of 19.1 A, consistent with the value predicted from the X-ray structure and the Stokes radius. As the equilibrium is shifted to favor I1 at approximately 3.2 M and I2 at 5.0 M urea, SEC and UC show that R(s) increases from approximately 38 to approximately 52 A. Measurements of the radius by DLS and SAXS between 2 and 4.5 M urea were complicated by the self-association of the I1 species at the relatively high concentrations required by those techniques. Above 6 M urea, SEC and UC reveal that R(s) increases linearly with increasing urea concentration to approximately 54 A at 8 M urea. The measurements of R(s) by DLS and R(g) by SAXS are sufficiently imprecise that both values appear to be identical for the I2 and U states and, considering the errors, are in good agreement with the results from SEC and UC. Thermodynamic parameters extracted from the SEC data for the N right harpoon over left harpoon I1 and I1 right harpoon over left harpoon I2 transitions agree with those from the optical data, showing that this technique accurately monitors a part of the equilibrium model. The lack of sensitivity to the I2 right harpoon over left harpoon U transition, beyond a simple swelling of both species with increasing urea concentration, implies that the Stokes radii for the I2 and U states are not distinguishable. Surprisingly, the hydrophobic core known to stabilize I2 at 5.0 M urea [Saab-Rincón, G., Gualfetti, P. J., and Matthews, C. R. (1996) Biochemistry 35, 1988-1994] develops without a significant contraction of the polypeptide, i.e., beyond that experienced by the unfolded form at decreasing urea concentrations. Kratky plots of the SAXS data, however, reveal that I2, similar to N and I1, has a globular structure while U has a more random coil-like form. By contrast, the formation of substantial secondary structure and the burial of aromatic side chains in I1 and, eventually, N are accompanied by substantial decreases in their Stokes radii and, presumably, the size of their respective conformational ensembles.

Recycling of urea associated with the host plant urease in the silkworm larvae, Bombyx mori

Urea concentration and urease activity in the midgut content were compared between larvae of the silkworm, Bombyx mori fed an artificial diet and those fed fresh mulberry leaves. A considerable amount of urea was found in the midgut content of the both larvae, however it was significantly lower in the larvae fed fresh mulberry leaves than in the larvae fed the artificial diet; average urea concentrations in the midgut content of the larvae fed fresh mulberry leaves and the artificial diet were 2.9 and 4.6 μmol/g, respectively. Urea in the midgut content seems to be secreted from the insect itself since the amount of urea in both diets were negligibly small. Urease activity was detected only in the midgut content of the larvae fed fresh mulberry leaves but not in other tissues of the larvae. On the other hand, no urease activity was detected in the midgut content of the larvae fed the artificial diet. Subsequently, to elucidate the role of mulberry leaf urease in the midgut lumen, larvae that had been reared on the artificial diet were switched to fresh mulberry leaves. The diet switch caused a rapid decrease in urea concentration in the midgut content and an increase in ammonia concentration in the midgut content, suggesting that secreted urea could be hydrolyzed to ammonia by mulberry leaf urease in the midgut lumen. Furthermore, to investigate the physiological significance of mulberry leaf urease on urea metabolism of the silkworm, 15N-urea was injected into the hemocoel, and after 12 h the larvae were dissected for 15N analysis. A considerable amount of 15N was found to be incorporated into the silk-protein of the larvae fed fresh mulberry leaves, but there was little incorporation of 15N into the silk-protein of the larvae fed the artificial diet. These data indicate that urea is converted into ammonia by the action of mulberry leaf urease in the midgut lumen and used as a nitrogen source in larvae fed mulberry leaves.

Antiferritin single-chain antibody: a functional protein with incomplete folding?

The pET(scF11) plasmid was constructed comprising the gene of a single-chain antibody against human ferritin. This plasmid encodes the leader peptide pelB followed by the heavy chain variable V H domain, (Gly 4Ser) 3 linker peptide, and light chain variable V L domain. The correctly processed scF11 antibody was expressed in Escherichia coli as an insoluble protein without the leader peptide. Purified soluble scF11 was obtained after solubilization in 6 M GdnHCl followed by a sequential dialysis against decreasing urea concentrations and ion-exchange chromatography. ScF11 demonstrated only a ∼8-fold decrease in the affinity ( K a=5.1×10 8 M −1 in RIA and 1.8×10 8 M −1 in ELISA) vs. the parent IgG2a/κ monoclonal antibody F11. The emission maximum of intrinsic fluorescence strongly suggests a compact conformation with tryptophanyl fluorophores buried in the protein interior, consistent with the functionality of the protein. However, scF11 demonstrated (i) the lack of denaturant-induced fluorescence `dequenching' effect characteristic of the completely folded parent antibody, and (ii) prominent binding, under physiological conditions, of a hydrophobic probe 8-anilino-1-naphthalenesulfonate (ANS) recognizing partially structured states of a protein. These findings are indicative of an incomplete tertiary fold that gives ANS access to the protein hydrophobic core. This work provides the first indication that the functional single-chain antibody scF11 displays some properties of a partially structured state and therefore may possess incomplete folding.

Comparative Effects of Recombinant Ovine Placental Lactogen and Bovine Growth Hormone on Galactopoiesis in Ewes

The effects of recombinant ovine placental lactogen and bovine growth hormone on milk yield, milk composition, and concentrations of blood hormones and metabolites were compared in ewes during an established lactation. Beginning on d 17 of lactation, ewes were treated for 5 d with twice daily subcutaneous injections of ovine placental lactogen (n=9), bovine growth hormone (n=10) at a dose of 0.10 mg/d per kg of body weight, or saline (n=10). Circulating concentrations of ovine placental lactogen were 24.6±1.6ng/ml on d 5 for ewes treated with ovine placental lactogen, but concentrations of ovine placental lactogen were undetectable in ewes treated with either saline or bovine growth hormone. Treatment with bovine growth hormone increased circulating concentrations of growth hormone, insulin-like growth factor-I, and nonesterified fatty acids and decreased urea concentrations relative to those in ewes treated with ovine placental lactogen or saline. Compared with saline treatment, no parameters were affected by treatment with ovine placental lactogen. Treatment with bovine growth hormone or ovine placental lactogen treatment had no significant effects on plasma concentrations of insulin, glucose, or creatinine. Treatment with bovine growth hormone, but not ovine placental lactogen, increased yields of milk, fat, and lactose. Weight of the mammary gland was increased by bovine growth hormone, but not by ovine placental lactogen. Despite the fact that ovine placental lactogen is a potent somatogen, it does not appear to exhibit the same galactopoietic activity as bovine growth hormone in lactating ewes.

Study of structure and function of recombinant pea root plastid porin by biophysical methods.

Pea root plastid porin (Fischer et al. (1994) J. Biol. Chem. 269, 25754-25760), which belongs to the family of mitochondrial (eukaryotic) porins, was expressed in Escherichia coli in high amounts using the pQE expression system. The recombinant protein was reconstituted into lipid bilayer membranes, and its characteristic properties were compared to those of the native porin isolated from pea root plastids. No significant difference was found between the native and the recombinant form when the protein was preincubated in detergent and sterol. The recombinant porin seems to be a valuable model system for the study of eukaryotic porins by spectroscopic methods, in which high amounts of protein are needed. CD spectroscopy was performed to determine the secondary structure of the porin under different conditions. It was found to have a high degree of beta-sheet structure in the nonionic detergent Genapol X-80 and in lipid vesicles. The more polar detergent sodium dodecyl sulfate (SDS) induced a large amount of alpha-helix structure in the protein. Addition of sterol to the porin in Genapol buffer did not influence its secondary structure to any measurable extent, whereas it had a strong influence on channel forming activity in black lipid bilayers. First refolding experiments performed in decreasing urea concentrations are discussed together with the results of the other measurements with regard to protein folding and channel formation.

Effect of protein nutrition on ammonia emission from a cubicle house for dairy cattle

The effect of protein nutrition on the urinary concentration of urea and subsequent emission of ammonia into the atmosphere was studied using a mechanically ventilated cubicle house containing 34 lactating dairy cows (cross bred Holstein Friesian and Dutch Friesian). Two silage-based diets with different amounts of rumen-degradable protein balance (OEB), were alternately fed during six 3-week periods. Diet L contained a small amount of OEB and resulted in a 39% lower emission rate, compared with diet H which contained a high amount of OEB. The concentration of urea in the urine samples was 42% lower when feeding diet L compared with diet H. A decrease in urea concentration as a result of a lower OEB could contribute substantially towards diminishing the emission of ammonia from cubicle houses for dairy cattle. L'effet de la nutrition protéique sur la concentration d'urée dans l'urine et l'émission correspondant d'ammoniaque dans l'atmosphère ont été étudiés en utilisant une étable à logettes avec ventilation mécanique, contenant 34 vaches laitières (croisées Holstein). Deux régimes à base d'ensilage avec différents niveaux de protéine dégradable dans le rumen (OEB) ont été distribués en alternance pendant six périodes de trois semaines. Le régime L contenait peu d'OEB et a permis de diminuer de 39% le rythme d'émission, par rapport au régime H qui contenait beaucoup d'OEB. La concentration d'urée dans les échantillons d'urine a été de 42% inférieure en régime L par rapport au régime H. Une diminution de la concentration en urée suite à une diminution de l'OEB pourrait contribuer de façon importante à la diminution de l'émission d'ammoniaque par les étables à logettes des vaches laitières. In einem mechanisch belüfteten Boxenstall, in dem 34 laktierende Milchkühe (Kreuzungen aus Holstein Friesian und Holländischen Schwarzbunten) gehalten wurden, ist der Einfluβ der Proteinernährung auf die Harnstoffkonzentration im Urin und die daraus folgende Ammoniakemission in die Atmosphäre untersucht worden. Zwei auf Silage basierende Rationen mit unterschiedlichem Gehalt an im Pansen abbaubarem Protein (OEB) wurden alternativ während sechs 3-Wochen- Perioden gefüttert. Die Ration L zeichnete sich durch einen geringen Gehalt an OEB aus und hatte eine um 39% geringere Emissionsrate im Vergleich zu der Ration H mit einem hohen Gehalt. Die Konzentration von Harnstoff im Urin war bei der Ration L um 42% geringer im Vergleich zur Ration H. Eine Reduzierung der Harnstoffkonzentration im Ergebnis einer geringeren Menge an im Pansen abbaubarem Protein könnte substantiell zur Verringerung der Emission von Ammoniak in Boxenställen für Milchkühe beitragen.

Amnio-Allantoic fluid exchange for the prevention of intestinal damage in gastroschisis: An experimental study on chick embryos

In gastroschisis, the protruding intestine is usually shortened, thickened, and covered with a fibrous peel. Urine components, which are increased in the amniotic fluid with the onset of renal function, are responsible for these changes. In the chick embryo model of gastroschisis, the authors performed amnio-allantoic fluid exchange to reduce the effect of urinary products. There were three study groups: control, gastroschisis only, and gastroschisis plus exchange. There was a significant decrease in creatinine ( P < .05) and a slight decrease in urea concentrations in the gastroschisisplus-exchange group compared with the gastroschisis-only group. Whereas macroscopic and microscopic studies showed severe fibrosis and bowel-wall thickening in the latter group, the bowel was normal or slightly oedematous in the former. On the basis of this study, the authors suggest that antenatal amniotic fluid exchange might reduce the bowel damage in human foetuses.

Preparation of titania colloids by thermal hydrolysis of urea and densification behavior of the collid-derived monolithic titania gels

Hydrous titania colloids with different sizes and shapes were prepared from urea-containing TiCl4 solutions by controlled thermal hydrolysis of urea. Very small colloidal particles (Sw=280–290 m2/g) with anatase structure were precipitated from aqueous HCl solutions of [TiCl4] 16.6 mol/dm3. Sols containing such colloids could be converted to translucent monolithic gels. A decrease in urea concentration ([urea]=8.3 mol/dm3) caused the production of aggregated rutile-type particles with a large aspect ratio, from which only titania powder was obtained. Heating of a monolithic gel above 500°C resulted in the accelerated densification of the gel. A highly densified titania with 96% of theoretical density was produced from the monolithic gel after heating at 700°C for 6 h.

Influence of ice storage on ray (raja clavata) wing muscle

AbstractDeterminations of pH, urea, extractable protein (EP), apparent viscosity (AV), water‐binding capacity (WBC), hardness (H), Hunter L, a and b values and sensory evaluation (SE) (raw and cooked), as well as microbiological analysis, were used to study the effects of ice storage on the stability of ray (Raja clavata) muscle. Significant changes were found in pH, bacterial growth and sensory assessment (ammoniacal odour and colour) during the storage period. Urea content, EP, AP, WBC (measured as water loss) and Hunter L value (in cooked muscle) decreased significantly. Statistical analyses did not show significant differences in H and Hunter L value (in raw muscle). The decrease in urea concentration can be described as a linear function of the number of microorganisms suggesting the microbiological character of the process. No dependence was observed between pH or number of microorganisms and EP, whereas AP was much more affected and showed a marked dependence on these two parameters treated independently. The results of this research showed that wings could be stored in ice for 9–10 days without causing important loss of quality. The fish was considered excellent up to day 7 and acceptable after 9 days but unacceptable after 11–12 days onwards. Nonetheless, the shelf‐life of the ray in the iced state can vary depending upon the initial state of freshness, handling and the biological conditions of the fish. Microbiological analysis, pH, EP, AV, WBC, SE and Hunter L value have been demonstrated to be factors which could be used to monitor the deterioration of ray during ice storage.

Use of Nonreducing SDS-PAGE for Monitoring Renaturation of Recombinant Protein Synthesis Initiation Factor, eIF-4α

The purification of biologically active human protein synthesis initiation factor 4α, eIF-4α, overexpressed in Escherichia coli, is complicated by its localization in insoluble inclusion bodies, as well as its possession of four cysteines. Two of these cysteines have been reported to be reduced in the native molecule and two form a disulfide bond. A method is described, using nonreducing sodium dodecyl sulfate polyacrylamide gel electrophoresis, for monitoring renaturation of the polypeptide during staged dialyses in decreasing urea concentrations. The production of biologically active eIF-4α only occurs when the polypeptide is totally reduced during solubilization of the inclusion bodies in 8 M urea. This requires a minimum dithiothreitol concentration of 50 mM. Conversely, reformation of the disulfide bonds only occurs when the staged dialyses are performed at lower concentrations of sulfhydryl reagents. Once renatured, as described, eIF-4α can be purified by affinity chromatography on m7GTP-Sepharose. Approximately 20 μg of biologically active eIF-4α per milliliter of bacterial culture can be obtained. The affinity-purified eIF-4α has activity equivalent to that reported for purified native human eIF-4α, as measured by its activity in a rabbit reticulocyte translation system. The method described is applicable to the purification of other cysteine-contaming polypeptides that accumulate to high levels in inclusion bodies.

Osmotically sensitive renin release from permeabilized juxtaglomerular cells

Renin secretion from juxtaglomerular (JG) cells is sensitive to external osmolality in a way that has been suggested to depend either on cellular volume or on effects on secretory granules. To distinguish between these possibilities, a technique for permeabilization of JG cell membranes was developed. Rat glomeruli with attached JG cells were isolated and permeabilized by 20 microM digitonin for 12 min and followed by continuous exposure to 2 microM digitonin. Experiments on proximal tubules showed that cellular volume was unaffected by changes in external sucrose concentration after a similar permeabilization procedure. With permeabilized JG cells the following changes in osmolality were tested (in mM sucrose): +90 (n = 6), +60 (n = 5), +30 (n = 6), +15 (n = 6), -15 (n = 5), -30 (n = 6), -60 (n = 6), and -90 (n = 6). With nonpermeabilized cells similar experiments were done with changes of +90 (n = 7), +30 (n = 4), -30 (n = 4), and -90 (n = 6) mM sucrose. Increases in osmolality caused inhibition of renin release, whereas decreases stimulated secretion. Within +/- 10% variations in osmolality there were no differences between the responses in permeabilized and intact cells, whereas the responses with larger changes were less in the permeabilized cells. Increase or decrease in urea concentration by 30 mM did not affect renin release. Thus water fluxes can influence renin release by a mechanism that is independent of cell volume.

The relationships between seasonal variations in the concentration of urea in bulk milk and the production and fertility of dairy herds.

The concentration of urea was measured in bulk milk samples taken on seven occasions during a period of 13 months from 1,658-1,815 of the 2,100 suppliers of milk to a dairy. The mean concentration of urea was significantly higher when the cows were grazing than when they were housed, but there were no significant variations within either of these periods. In herds with very low milk urea concentrations while they were housed (< 2.4 mmol/l) the mean increase during the grazing season was approximately 2.0 mmol/l, whereas in herds with very high urea concentrations while they were housed (> 6.0 mmol/l) there was a slight decrease in urea concentration during the grazing season. The annual milk yield of herds with low urea concentrations was significantly lower than the yield of herds with intermediate or high concentrations. The interval between calving and first insemination was significantly longer in herds with low milk urea concentrations, but these herds also had a higher 56-day non-return rate.

The effects of porcine somatotropin (pST) dosage and dietary lysine level on growth performance and carcass characteristics of finishing swine (1988)

One hundred and forty-four finishing pigs (initial weight 126 lb) were utilized to determine the effects of PST dosage (4 or 8 mg PST' head^-1day^-1 ) and dietary lysine level (.8, 1,0, 1.2, or 1.4%) on growth performance and carcass characteristics. Pigs were injected daily in the extensor muscle of the neck with either 4 or 8 mg PST and fed a pelleted corn-soybean meal-sesame meal diet containing .8% lysine. Additional lysine levels of 1.0, 1.2, and 1.4% were provided by L-lysine HCl. Control pigs (placebo injection) received the .8% lysine diet. All diets were formulated to contain at least 220% of NRC (1979) recommendations for other amino acids, vitamins and minerals. There were no PST x lysine interactions for any observed traits (P>,1 0), so only main effects are reported. Increasing level of dietary lysine resulted in linear improvements in average daily gain (ADG) and feed conversion (F/G) in PST treated pigs. Adjusted backfat thickness (ABF) was lowered (linear P<.05), whereas longissimus muscle area (LMA) was increased (linear P<.05) with increasing lysine level. Pigs injected with 8 mg PST had similar ADG compared to 4 mg PST-treated pigs, and both were greater than controls (linear and quadratic P < .05%). Increasing PST dosage improved F/G (linear and quadratic P < .05), LMA and reduced ABF (linear P < .05). Urea concentrations determined in plasma on day 28 decreased (linear and Quadratic P<.05) with increasing lysine level, whereas free fatty acids and insulin tended to increase (P<.10). Porcine somatotropin dosage decreased urea concentrations while glucose, insulin and free fatty acid concentrations increased (linear and quadratic P < .05) in plasma. Trimmed ham and loin weights were increased slightly (P >.10) by increasing dietary lysine level and were also increased (linear P < .10) by PST dosage.; Swine Day, Manhattan, KS, November 17, 1988

Complete separation of the triplet components of neurofilament by DE-52 column chromatography depends upon urea concentration

In the separation of the triplet components of neurofilament (P 200, P 160, and P 68) by DE-52 column chromatography in the presence of urea, it was revealed that the efficiency of separation depended upon urea concentration. When chromatography was performed in the presence of 8 m urea and a linearly increasing sodium phosphate concentration from 10 to 400 m m at pH 6.8, P 160 and P 68 were eluted in the same peak, although P 200 was eluted faster. P 160 and P 68 were partially separated with 6 m urea, and completely separated with 4 m urea. But, under these conditions, P 200 was eluted at the same position as contaminated glial fibrillary acidic protein (GFA). From these results, two methods were recommended for the complete separation of the triplet components of neurofilament and GFA by DE-52 column chromatography. In one method, chromatography was performed in the presence of 8 m urea at first, and then P 160 and P 68 were separated in the presence of 4 m urea. In the other method, chromatography was performed with a linearly decreasing urea concentration from 8 to 0 m.

Effects of Long Supplementation with Lipids on Lacting Dairy Cows

Effects of long term feeding of large amounts of an oil seed supplement treated with formalin upon metabolite patterns in blood of the dairy cow, milk composition, and general performance were studied. Cholesterol and cholesterol esters in plasma rose to 1000 mg/100ml at peak lactation when lipid intakes were declined in later lactation. High concentrations of cholesterol did not induce hemolytic anema. Concentrations of nonesterified fatty acid in serum peaked at 700 microequivalents per liter when lipid intakes were greatest and declined thereafter. The pattern of triacylglycerol concentrations in plasma seemed to reflect both lipid intake and mammary uptake. No changes in blood hematocrite, hemoglobin content, plasma protein, amino acid nitrogen, urea glucose, aspartate aminotransferase, or creatine phosphokinase were noted, excepting a temporary decrease in urea concentrations when initiating feeding of the supplement. Milk protein and lactose contents were unaffected by the supplement while percentage of milk fat was increased. Since the supplement was high in linoleate, a major increase was in percentage of this fatty acid in milk fat. Changes in the fatty acid pattern in milk fat adjusted rapidly to the change in diet and remained constant thereafter. There was indication that the supplement increased lactational performance during early lactation. This apparent advantage was more than offset by a subsequent depression in milk yields and shortcoming of lactation in several cows under the ad lib feeding regime. if high lipid supplements are to be used in practice, research on appropriate feeding regimes is required.

Lability of renal papillary tissue composition in the rat.

1. The acute effects of (a) a minor operative procedure using ether as the anaesthetic, and (b) the administration of 0.9% saline as a single I.V. injection in the conscious rat, on renal tissue composition were studied in hydropenic and normally hydrated rats. 2. The operative procedure and anaesthesia induced a rapid and transient decrease in papillary osmolality in both hydropenic and normally hydrated animals, the important contributing factor being a significant decrease in urea content. 3. Administration of a small volume of saline caused a rapid decrease in urea content, and an increase in water content. 4. It is concluded that papillary composition is extremely labile, large changes being produced by relatively minor experimental procedures.

Collecting duct dlow rate as a determinant of equilibration between urine and renal papilla in the rat in the presence of a maximal antidiuretic hormone concentration.

1. Antidiuretic hormone (ADH) was infused into normal male rats at a rate of 60 muu./min. 100 g body wt., to maintain an effectively constant maximal circulating level. Four groups of rats were used; they were water-loaded by receiving together with the ADH, I.V. infusions of hypotonic dextrose (2.5 g/100 ml.) at different rates (1.0, 4.5, 9.0 and 12 ml./hr, respectively), over an infusion period of 4 hr.2. Urine flow rate increased in all groups, the rate and extent of the increase being related to the volume rate of infusion. The differences in urine flow rates between the four groups were due almost entirely to increases in free water clearance, with no consistent differences in osmolal clearance between the groups. At the end of the 4 hr infusion period, osmolal clearances were closely similar in the four groups.3. Papillary and medullary tissue solute concentrations were progressively reduced at the higher rates of infusion. The changes were due to small increases in the water content, together with a profound decrease in urea concentration and a smaller decrease in sodium concentration. However, papillary osmolality was consistently higher than urine osmolality at the three highest rates of dextrose infusion.4. As urine flow rate increased, there was a progressive reduction in the degree of osmotic equilibration between the final urine and the papillary tip. For urea, however, the degree of equilibration remained high.5. It is concluded that, in the rat, the rate of flow per se, along the collecting duct, is an important determinant of final urine concentration; even if there is an osmotic driving force for water re-absorption in the renal medulla, and the collecting duct walls are permeable to water, osmotic equilibration is restricted by tubular flow rate.

Time course of changes in renal tissue and urinary composition after cessation of constant infusion of lysine vasopressin in the conscious, hydrated rat.

1. The changes in urinary and renal tissue composition in conscious rats were determined for up to 2 hr following the cessation of intravenous infusion of lysine vasopressin, LVP (at 60 muu./min. 100 g body wt. for 4(1/2) hr). A constant water load (4% body wt.) was maintained during and after lysine vasopressin infusion, by quantitative replacement of excreted water. In these circumstances, any changes in urinary and renal tissue composition are presumed to represent direct consequences of the rapid plasma and tissue clearance of lysine vasopressin.2. Urinary flow increased and osmolality decreased, rapidly, reaching stable values characteristic of sustained water diuresis after about 60 min.3. The steepness of the corticomedullary solute concentration gradients also decreased rapidly. Papillary Na and urea concentrations fell to values characteristic of sustained water diuresis in about 45 min.4. The changes in medullary composition were compounded of a moderate significant increase in water content, a moderate, significant decrease in Na content, and a profound decrease in urea content.5. In the eventual steady-state water diuresis, urinary outputs of Na and K were significantly lower, and of NH(4) significantly higher, than those observed in control experiments where LVP infusion was continued for the corresponding 2 hr.6. It is concluded that the diuresis following the cessation of LVP infusion is due not merely to reduced nephron permeability to water but also to a rapid reduction in the osmotic force responsible for water reabsorption from the collecting duct.

Changes in the Composition of the Urine in Sigmoid Loop Bladders: A Comparison with Ileal Loops

In 5 patients with sigmoid loop urinary diversions, the sodium, potassium, and urea concentrations in the urine from the ureters and from the sigmoid loop were compared. Sodium and potassium were treated rather indifferently by the sigmoid segment as there was little or no significant difference between concentrations in the ureteral and the sigmoid loop urines. Three patients had a decreased urea concentration in the sigmoid loop urine, suggesting a transportation into the blood from the urine. In comparison with a corresponding study on ileal loop urinary diversion, the sigmoid loop showed little tendency towards changes in the urinary composition. Therefore, sigmoid loop urinary diversion is recommended for patients with an impaired kidney function.

Effects of 0-9 per cent saline infusion on urinary and renal tissue composition in the hydropaenic, normal and hydrated conscious rat.

1. Changes in water and solute outputs of hydropaenic, normal and hydrated conscious rats were determined during intravenous infusion (0.2 ml./min) of isotonic (0.9%) saline for 4 hr; renal tissue composition was determined before, and after 1 or 2 hr, infusion.2. In normal and hydrated rats increased excretion of water and sodium was such that urinary output matched intravenous input from about 2 hr. In hydropaenic rats, the diuretic and natriuretic response was much reduced; a retention of infused saline, equivalent to 15% body weight, occurred over 4 hr.3. A considerable increase in urea output and clearance, and a smaller increase in potassium and ammonium outputs, occurred in all groups.4. The corticomedullary osmolal gradients characteristic of non-diuretic rats were largely dissipated during saline infusion: by 1 hr in normal and hydrated rats, and by 2 hr in the hydropaenic group.5. These changes were ascribable mainly to an increase in tissue water content in all segments, particularly in the hydropaenic group; and to a profound decrease in urea content in all groups.6. Changes in tissue sodium content were smaller, and differed between segments and between the differently hydrated groups. A decrease in papillary content occurred in hydropaenic and normal groups and an increase in cortical and outer medullary content occurred in all groups.7. After 2 hr saline infusion, incomplete papillary-urinary osmotic equilibration was evident in all groups.8. These changes in medullary osmolality and in papillary-urinary osmotic equilibration preceded the maximal diuresis, and must contribute to the diuresis induced by saline infusion, as in water and osmotic diureses.