Showing papers on "Urea published in 1968"

Formation of Malonaldehyde from Phospholipid Arachidonate during Microsomal Lipid Peroxidation

Abstract: The thiobarbituric acid reacting material produced during enzymatic microsomal lipid peroxidation has been identified as malonaldehyde. The malonaldehyde was condensed with urea to form 2-hydroxy-pyrimidine, which was identified by its ultraviolet spectrum, chromato-graphic properties, and mass spectrum. Incubations with phosphatidyl choline labelled with tritiated arachidonate yielded 2-hydroxy-pyrimidine with a specific activity nearly equal to that of the phospholipid arachidonate. Incubations with tritiated arachidonic acid yielded 2-hydroxy-pyrimidine with a specific activity nearly 2 orders of magnitude less than that of free arachidonic acid. Therefore, phospholipid arachidonate has been established as the major source of the malonaldehyde produced during microsomal lipid peroxidation.

Antibacterial activity of human urine

Abstract: The fate of bacteria in human urine was studied after inoculation of small numbers of Escherichia coli and other bacterial strains commonly implicated in urinary tract infection. Urine from normal individuals was often inhibitory and sometimes bactericidal for growth of these organisms. Antibacterial activity of urine was not related to lack of nutrient material as addition of broth did not decrease inhibitory activity. Antibacterial activity was correlated with osmolality, urea concentration and ammonium concentration, but not with organic acid, sodium, or potassium concentration. Between a pH range of 5.0-6.5 antibacterial activity of urine was greater at lower pH. Ultrafiltration and column chromatography to remove protein did not decrease antibacterial activity. Urea concentration was a more important determinant of antibacterial activity than osmolality or ammonium concentration. Increasing the urea of a noninhibitory urine to equal that of an inhibitory urine made the urine inhibitory. However, increasing osmolality (with sodium chloride) or increasing ammonium to equal the osmolality or ammonium of an inhibitory urine did not increase antibacterial activity. Similarly, dialysis to decrease osmolality or ammonium but preserve urea did not decrease inhibitory activity. Decreasing urea with preservation of ammonium and osmolality decreased antibacterial activity. Removal of ammonium with an ion exchanger did not decrease antibacterial activity, whereas conversion of urea to ammonium with urease and subsequent removal of the ammonium decreased antibacterial activity. Urine collected from volunteers after ingestion of urea demonstrated a marked increase in antibacterial activity, as compared with urine collected before ingestion of urea.

Transfer of urea nitrogen across the rumen wall.

Abstract: HOUPT, T. RICHARD, AND KATHERINE A. HOUPT. Transfer of urea nitro,gen across the rumen wall. Am. J. Physiol. 2 1 /t(6) : 1296-1303. 1968.-Net movement of urea N across the wall of Pavlov-type rumen pouches was measured in three goats and one sheep as urea concentration difference between pouch and blood was varied. When urease activity of the rumen epitheliurn was depressed by vigorous rinsing or by treatment with antibacterial agents, a large portion of the blood urea that was transferred appeared in the pouch unchanged. Under these conditions transfer of urea N in either direction was linearly related to urea concentration difference and extrapolation of results indicated that transfer would cease at zero concentration difference. When urease activity was undisturbed, nearly all urea transferred was hydrolyzed to NH,; and at normal blood urea levels transfer of urea N was increased manyfold (up to 13 times). It appears that urea per se moves through the rumen wall by diffusion. However, under normal rumen conditions, blood urea is hydrolyzed before all epithelial diffusion barriers are crossed, and the NH3 then diffuses more rapidly than urea would through the remaining epithelial layers. The over-all effect is to enhance transfer of urea N from blood into the rumen.

The ‘neurotoxicity’ of l-2,4-diaminobutyric acid

Abstract: The neurolathyrogen l-2,4-diaminobutyric acid is concentrated by liver, and liver damage can yield neurotoxicity; thus the neurotoxicity caused by this compound may be due to liver damage followed by secondary brain damage. 1. The intraperitoneal administration of toxic doses of l-2,4-diaminobutyric acid to rats resulted in hyperirritability, tremors and convulsions in 12–20hr. and increased the concentration of ammonia of blood and brain slightly and the concentration of glutamine of brain two- to three-fold. By contrast, toxic doses of l-homoarginine, l-lysine, l-leucine and ammonium acetate caused dyspnoea, extreme prostration, and in some cases coma in 15–30min., and increased the concentration of ammonia of blood significantly and the concentration of glutamine of brain slightly. These results indicate that l-2,4-diaminobutyric acid caused a chronic ammonia toxicity, whereas the other amino acids and ammonium acetate resulted in an acute ammonia toxicity. 2. Liver slices from l-2,4-diaminobutyric acid-treated animals and normal liver slices preincubated with l-2,4-diaminobutyric acid utilized ammonia and formed urea at a lower rate than control slices from normal rats. 3. l-2,4-Diaminobutyric acid inhibited competitively ornithine carbamoyltransferase of rat liver homogenates, thus demonstrating that this reaction is a primary site of toxicity for this neurolathyrogen. Although we were unable to show marked elevations of blood ammonia concentration after treatment with l-2,4-diaminobutyric acid, these results are interpreted to mean that ammonia utilization (urea synthesis) in liver is inhibited by l-2,4-diaminobutyric acid and that at least part of the neurotoxicity is due to a prolonged slight increase in body ammonia concentration.

The time course of changes in renal tissue composition during mannitol diuresis in the rat.

Abstract: 1. The time course and extent of changes in the composition of renal tissue slices in water diuresis were determined by sacrificing groups of rats before and during the intravenous infusion of dextrose (2·5 g/100 ml.) in amounts sufficient to administer over 2 hr, and subsequently to maintain for up to 7½ hr, a positive fluid load of 4% body weight. 2. The corticomedullary osmolal gradient characteristic of the nondiuretic rats was progressively dissipated until, at 7½ hr, only papillary tip concentrations were higher than those of other segments. 3. The changes in individual constituents followed different time courses: (i) an increase in water content in all segments, particularly the papilla, was almost complete by 1 hr, preceding the maximal increases in urine flow; (ii) a marked decrease in papillary and medullary urea content in the first hour was followed by a slower, progressive decrease leading to an almost complete dissipation of the urea gradient by 7½ hr; (iii) small, non-significant decreases in sodium content occurred in all segments in the first hr, followed by a further small, progressive decrease in papillary sodium content; (iv) changes in ammonium and potassium concentrations were mainly related to those in water content, since the contents of these solutes showed only small changes. 4. By 2 hr, differences in the rates of decline of osmolal and urea concentrations in urine and papilla led to urinary concentrations significantly lower than papillary values. The steep papilla-urine urea concentration difference became smaller, but remained significant even at 7½ hr. 5. The findings are discussed in terms of changes in countercurrent mechanisms, particularly as influenced by anti-diuretic hormone. 6. The development of papilla/urine urea concentration ratio greater than unity is also considered in terms of passive transport with changes in membrane permeability.

Development of urea-synthesizing enzymes in human liver.

Abstract: Summary Liver slices from human foetuses of a gestational age between 16 and 20 weeks produce urea when incubated with optimal amounts of substrate. The activities of the enzymes which synthesize urea (carbamyl phosphate synthetase, ornithine transcarbamylase, arginine synthetase system, argininosuccinase and arginase) have been measured in human liver during development. No rapid postparturition increase in activity was discernible in any of the enzymes studied, although in general the adult levels were somewhat higher than those found at birth. Arginine synthetase has the lowest relative activity of all the five enzymes involved in urea synthesis. The apparent Km for citrulline is similar in magnitude for both foetal and adult liver arginine synthetase.

Nitrogen metabolism in the terrestrial isopod, Oniscus asellus.

Abstract: The total diffusible content of ammonia in Oniscus asellus was measured as 1.20 mg % body fluid. Daily excretions of ammonia exceeded the total diffusible content in measurements on specimens taken directly from nature. The content of uric acid in a group of 35 specimens was 11.3 mg % body weight and 93% of this material was in the body wall. Urea was not measurable under conditions that would have allowed detection of at least 0.26 mg % body fluid. Only arginase of the enzymes in the ornithine-urea cycle was measurable. Labeled urea was not detectable in aqueous extracts under conditions where approximately 50,300 CPM of labeled carbon was incorporated into metabolites. Labeled arginine was not detectable under conditions where 9,100 CPM of KHC14O3 were incorporated into the soluble protein fraction and more than 3,340,000 CPM were incorporated into particulate protein and non-protein fractions of the organism. All of the enzymes of uricolysis to ammonia were present, uricase and urease being rate-limiting. Uricase was measurable as myeloperoxidase. Although high rates of glutamate-oxalacetate aminotransferase and glutamate-pyruvate aminotransferase were readily measured, glutamic dehydrogenase activity proceeded slowly, suggesting synthesis of needed amino acids as the key function of the transaminase activities. Amino acid oxidase activities, glutaminase, and asparaginase activities were low, too, whereas peroxidatic deaminase activities proceeded at rates sufficiently fast to account for the levels of volatile ammonia emitted in vivo . Although molting may serve for excretion of end-products of purine catabolism, no central organ homologous to kidney or liver appears to be present with respect to detoxication or excretion of ammonia. Inasmuch as O. asellus is not exposed to osmotic stresses, does not ordinarily face problems of dehydration, and tolerates levels of ammonia generally ascribed as toxic to other organisms, it is proposed that retention of ammonotelism probably offers thermodynamic advantages to the organism. The evolution of a system wherein ammonia is excreted as a gas may have provided the organism with an adaptive mechanism for colonizing land.

Effects of water diuresis and osmotic (mannitol) diuresis on urinary solute excretion by the conscious rat

Abstract: 1. The time course and extent of changes in urinary flow and in the outputs of urea, Na+, K+, and NH4+ over a period of 7½ hr in conscious rats during water and osmotic (mannitol) diuresis were determined, and compared with spontaneous changes in non-diuretic animals. 2. In non-diuretic rats, a morning rise and subsequent decline in urinary osmolal, sodium, potassium and ammonium outputs occurred, possibly attributable to circadian rhythms. 3. Water diuresis was accompanied by (i) a rapid increase in urea excretion during the phase of increasing urine flow, followed by a fall in later periods to values similar to those in non-diuresis, (ii) a slower increase in sodium output, continuing after the establishment of the constant water load, (iii) unchanged potassium excretion, but slightly increased ammonium outputs. 4. Mannitol diuresis was accompanied by (i) a rapid increase in urea outputs which subsequently fell but remained significantly higher, (ii) a steep rise in sodium and potassium outputs to values which remained far higher than those in non-diuretic and water diuretic animals. 5. The changes in mannitol diuresis are considered to result mainly from decreased tubular reabsorption, due to the lowered intraluminal sodium, potassium and urea concentrations and increased intratubular fluid flow. Some of the acute increase in urea excretion may be due to washout of medullary urea into the tubular fluid. 6. In water diuresis, some of the changes in solute excretion may similarly result from altered tubular reabsorption, perhaps influenced by suppression of anti-diuretic hormone (A.D.H.). In addition, the slower changes in sodium output may be related to several consequences of change in body fluid volume.

Semipermeable aqueous microcapsules (artificial cells). V. Permeability characteristics

Abstract: A rapid mixing and sampling technique was used to study the permeability characteristics of semipermeable aqueous microcapsules (artificial cells). Urea, creatine, creatinine, uric acid, glucose, sucrose, and salicylic acid equilibrated rapidly across nylon microcapsules of 207 μ diameter (e.g., T1/2 for urea of 3.4 sec). From these results the permeability constants were calculated (e.g., P for urea of 2 × 10−4 cm/sec). Very much the same permeability constants were found for collodion microcapsules. The equivalent pore radius of the membrane of the nylon microcapsules were estimated to be 18 A.