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PubMed1998

Characteristics of urea transport of cells derived from rabbit thick ascending limb of Henle's loop.

BACKGROUND: The thick ascending limb of Henle's loop (TALH) is thought to be involved in the regulation of the renal urea gradient. METHODS: We have characterized the uptake of urea (oil density centrifugation and 2-compartment-culture) and volume regulation (impedance measurement) in highly differentiated cells derived from rabbit outer medulla. RESULTS: TALH cells exposed to 600 mOsm/liter (300 mM urea) shrunk to 72 +/- 5% of the isoosmotic volume. Due to a regulatory volume increase (RVI), the cell volume was almost completely regained at 92 +/- 6% after five minutes. The uptake of 14C-urea in the presence of urea concentrations up to 600 mM did not show any saturation. In the presence of phloretin the urea uptake decreased to 69 +/- 14%. The transport was sodium and chloride independent. Changing the membrane potential caused an increase of regulatory volume increase and urea uptake. Hyperosmolarity induced by sucrose (300 mM) and NaCl (150 mM) caused a decrease of urea uptake to 70 +/- 14% and 53 +/- 11%, respectively. The permeability coefficient (P) in a two compartment culture was P = 1.7 . 10(-6) +/- 0.39.10(-6) cm/second, suggesting a relatively low permeability. CONCLUSION: Due to the low permeability, it seems impossible to achieve a physiologically significant participation of the TALH in the urea circulation within the nephron. However, the results of this study provides significant hints about the existence of a specific urea transport mechanism that enables the cell to adapt rapidly to different osmolarities.

Acetamides↗
PubMed1982

Hydroxyl radical scavengers inhibit lymphocyte mitogenesis.

Agents that are known to be scavengers of hydroxyl radicals inhibit lymphocyte mitogenesis induced by phorbol myristate acetate (PMA) to a greater extent than they inhibit mitogenesis induced by concanavalin A or phytohemagglutinin. These agents include dimethyl sulfoxide, benzoate, thiourea, dimethylurea, tetramethylurea, L-tryptophan, mannitol, and several other alcohols. Their inhibitory effect is not associated with cytotoxicity. The hydroxyl radical scavengers do not inhibit PMA-dependent amino acid transport in T cells or PMA-induced superoxide production by monocytes. Thus, they do not inhibit the primary interaction of PMA with responding cells. Treatment of peripheral blood mononuclear cells with PMA increased cellular guanylate cyclase in most experiments, and dimethyl sulfoxide tended to inhibit this increase. In addition to inhibition of PMA-induced mitogenesis, hydroxyl radical scavengers markedly inhibited the activity of lymphocyte activating factor (interleukin 1). The differential inhibition of lymphocyte mitogenesis induced by different mitogens appears to be related to the differential macrophage requirements of the mitogens. The data suggest that hydroxyl radicals may be involved in mediating the triggering signal for lymphocyte activation. Some of the hydroxyl radical scavengers are inducers of cellular differentiation,. nd it is possible that their differentiating activity is related to their ability to scavenge free radicals.

Benzoates↗
PubMed1994

Selection of multiple human immunodeficiency virus type 1 variants that encode viral proteases with decreased sensitivity to an inhibitor of the viral protease.

Inhibitors of the human immunodeficiency virus type 1 (HIV-1) protease represent a promising addition to the available agents used to inhibit virus replication in a therapeutic setting. HIV-1 is capable of generating phenotypic variants in the face of a variety of selective pressures. The potential to generate variants with reduced sensitivity to a protease inhibitor was examined by selecting for virus growth in cell culture in the presence of the protease inhibitor A-77003. Virus variants grew out in the presence of the inhibitor, and these variants encoded proteases with reduced sensitivity to the inhibitor. Variants were identified that encoded changes in each of the three subsites of the protease that interact with the inhibitor. HIV-1 displays significant potential for altering its interaction with this protease inhibitor, suggesting the need for multiple protease inhibitors with varying specificities.

Amino Acid Sequence↗
PubMed2003

Determination of the herbicide isoproturon in cereal grains and pasta by LC with LC/MS confirmation.

A method was developed for the determination of the herbicide isoproturon in wheat, maize, oats and pasta, with a limit of determination of 0.05 mg kg(-1). Isoproturon was extracted from moistened samples using a mixture of acetone, hexane and dichloromethane. The resulting extract was cleaned-up by solid-phase extraction using aminopropyl-bonded silica cartridges and analysed by reversed-phase liquid chromatography with photodiode array detection. Confirmation was by electrospray liquid chromatography-mass spectrometry. Recoveries from seven samples of each of the four matrices spiked with isoproturon at 0.05 and 0.5 mg kg(-1) were in the range 88-104%. The method was used to monitor cereal grains and pasta as part of the UK food monitoring programme.

Avena↗
PubMed1976

Contributions to ecological chemistry CXII1. Balance of conversion of buturon-14C in wheat under outdoor conditions.

The urea herbicide buturon (N-[p-chlorophenyl]-N'-methyl-N'-isobutinyl-urea), 14C-labeled, was sprayed on winter wheat as an aqueous formulation (2.98 kg/ha) under outdoor conditions. Upon harvest (three months after application), a total of 49.2% of the applied radiocarbon was recovered: 2.0% in the plants, 46.9% in the soil, and 0.3% in the leaching water (depth greater than 50 cm); less than 0.1% was in the grains (0.464 ppm). Only about half of the radioactivity present in plants could be recovered under mild extraction conditions; about half of this was unchanged buturon. In straw and husk extracts, the following metabolites were identified by gaschromatography/mass spectrometry:N-(p-chlorophenyl)-N-methyl-O-methyl-carbamate (metabolite I), N-phenyl-N'-formyl-urea (metabolite II), two unstable metabolites giving (p-chlorophenyl)-isocyanate upon purification (metabolites III and IV), N-(p-chlorophenyl)-N'-methyl-N'-isobutenylol-urea (metabolite V), p-chloroformanilide (metabolite VI) and biologically bound p-chloroaniline (metabolite VII). In the root and basal stem extract, the following metabolites were identified by gas chromatography/mass spectrometry: N-(p-chlorophenyl)-O-methyl-carbamate (metabolite VIII) and N-(p-chlorophenyl)-N'-methyl-urea (metabolite IX).

Chromatography, Gas↗
PubMed1979

Persistence and movement of chlorbromuron in potato soil.

Movement and persistence of chlorbromuron applied at rates of 1.5, 3, and 6 kg a.i./ha was studied in a New Brunswick potato soil for one growing season. Most of the chlorbromuron remained in the 0 - 2.5 cm soil depth with slight residues in the 2.5 - 5, 5 - 7.5, and 7.5 - 10 cm depths. After 47 days the chlorbromuron residues had dropped to 40%, then gradually levelled off to 25% at the end of the season. Chlorbromuron was determined directly by electron capture gas chromatography using a short glass column of 3% OV-210.

Chromatography, Gas↗
PubMed1998

Herbicide residues in leaves of Erythroxylum coca var. coca plants treated with soil-applied tebuthiuron and hexazinone.

The herbicide residue levels in leaves of Erythroxylum coca var. coca Lam. plants treated with soil applications of tebuthiuron and hexazinone at 3.36 and 6.72 kg a.i. ha-1 were determined in order to estimate the potential for human exposure to these residues from consuming the leaves or cocaine produced from them. Field-grown plants were treated with a commercial formulation of tebuthiuron or hexazinone and leaves were harvested at the first indication of herbicide injury (i.e. chlorosis and/or necrosis) and at the onset of leaf abscission. Herbicide residues were detected by HPLC in leaf samples from both harvests of all plants treated with tebuthiuron or hexazinone. At 3.36 kg ha-1, herbicide residues in the leaves were less than 2 micrograms g-1 dry wt. for both harvests of both experiments. The highest residue levels detected were 5.90 micrograms g-1 dry wt. for tebuthiuron and 7.17 micrograms g-1 dry wt. for hexazinone in leaves from plants treated with the herbicide at the rate of 6.72 kg ha-1 and harvested at the onset of leaf drop. Based on published toxicity data and estimates of leaf consumption, the herbicide residues in leaves of E. coca var. coca plants treated with tebuthiuron or hexazinone at twice the recommended control rates or less would have a negligible contribution to the health risks of individuals who chew coca leaves. Furthermore, based on the most conservative estimates of cocaine yield and herbicide carry over, death by cocaine overdose would occur long before the NOEL for either herbicide was reached.

Cacao↗
PubMed1999

Sorption and desorption kinetics of diuron, fluometuron, prometryn and pyrithiobac sodium in soils.

The sorption and desorption characteristics of four herbicides (diuron, fluometuron, prometryn and pyrithiobac-sodium) in three different cotton growing soils of Australia was investigated. Kinetics and equilibrium sorption and desorption isotherms were determined using the batch equilibrium technique. Sorption was rapid (> 80% in 2 h) and sorption equilibrium was achieved within a short period of time (ca 4 h) for all herbicides. Sorption isotherms of the four herbicides were described by Freundlich equation with an r2 value > 0.98. The herbicide sorption as measured by the distribution coefficient (Kd) values ranged from 3.24 to 5.71 L/kg for diuron, 0.44 to 1.13 L/kg for fluometuron, 1.78 to 6.04 L/kg for prometryn and 0.22 to 0.59 L/kg for pyrithiobac-sodium. Sorption of herbicides was higher in the Moree soil than in Narrabri and Wee Waa soils. When the Kd values were normalised to organic carbon content of the soils (Koc), it suggested that the affinity of the herbicides to the organic carbon increased in the order: pyrithiobac-sodium < fluometuron < prometryn < or = diuron. The desorption isotherms were also adequately described by the Freundlich equation. For desorption, all herbicides exhibited hysteresis and the hysteresis was stronger for highly sorbed herbicides (diuron and prometryn) than the weakly sorbed herbicides (fluometuron and pyrithiobac-sodium). Hysteresis was also quantified as the percentage of sorbed herbicides which is not released during the desorption step (omega = [nad/nde - 1] x 100). Soil type and initial concentration had significant effect on omega. The effect of sorption and desorption properties of these four herbicides on the off-site transport to contaminate surface and groundwater are also discussed in this paper.

Adsorption↗
PubMed1984

In vivo formation of nitrosocarbamates in the stomach of rats and guinea pigs.

The N-nitrosocarbamates are potent mutagens and carcinogens, and have been synthesized under acid conditions that prevail in the human stomach. However, it has never been documented that nitrosocarbamates are actually formed in vivo in the stomach of any mammalian species. Using 14C-labeled carbaryl and carbofuran, attempts were made to isolate the nitroso derivatives from the stomach contents of rats and guinea pigs treated orally with the carbamate and sodium nitrite. Only trace quantities of nitrocarbamate were recovered from the rat stomach, whereas 0.5 to 2.0% of the carbamate doses were isolated as the nitroso derivative from the contents of the guinea pig stomach. The rather low apparent yields resulted in part from the instability of the nitrosocarbamates and from absorption of the carbamate and/or nitrosocarbamate from the stomach. Higher rates of synthesis were indicated by incubating the carbamates with sodium nitrite in the presence of the stomach contents at 37 degrees C for 15 min. About 30% nitrosation occurred with the guinea pig and about 0.5% with the rat. The difference was attributed to the pH of the gastric contents. For the rat, the pH ranged from 3 to 5; gastric contents of the guinea pig had a pH between 1 and 2. Since the pH of the human stomach is also in the pH 1-2 range, it is likely that nitrosation of carbamates in humans would be very similar to that in the guinea pig.

Animals↗
PubMed2001

Developmental toxicity study of tetramethylurea (TMU) in rats.

The developmental toxicity of tetramethylurea (TMU) was assessed in rats by inhalation exposure of the test material over days 6-20 of gestation. Groups of 25 mated female Crl:CD BR rats were exposed whole-body for 6 hours/day to concentrations of either 0, 2, 20 or 100 ppm TMU. The dams were euthanized on day 21 and the offspring were weighted, sexed, and examined for external, visceral, and skeletal alterations. Maternal toxicity was demonstrated at both 20 and 100 ppm. Maternal body weights, weight changes, and food consumption were statistically significantly reduced at these concentrations; effects were more pronounced at 100 ppm. There was evidence of developmental toxicity only at 100 ppm. The only finding was a decrease in mean fetal weight. No fetal malformations or variations occurred in fetuses derived from rats exposed to all 3 test concentrations (up to 100 ppm). The maternal no-observed-effect-level (NOEL) was 2 ppm, the fetal NOEL was 20 ppm. Thus, TMU was not considered to be uniquely toxic to the rat conceptus.

Administration, Inhalation↗
PubMed2001

Adsorption of methabenzthiazuron on six allophanic and nonallophanic soils: effect of organic matter amendment.

This article reports on methabenzthiazuron [1-(1,3-benzothiazol-2-yl)-1,3-dimethylurea] (MBT) adsorption process on six agricultural allophanic and nonallophanic soils. The effect of amendment with exogenous organic matter was also studied. Adsorption kinetic fits an hyperbolic model. MBT adsorption reached an apparent equilibrium within 2 h and followed a second-order reaction. The maximum adsorbed amounts for natural soils ranged from 32 to 145 microg g(-1). Rate constants were considered relatively low (0.27-1.5 x 10(-4) [microg g(-1)](1-n) s-1); the slow process was attributed to a combined effect of difussion and adsorption. MBT adsorption fits the Freundlich model with r values > or =0.998 at P < or = 0.001 significance levels. Kf and Freundlich exponents (l/n) ranged from 5.3 to 82.1 cm3 g(-1) and from 0.66 to 0.73, respectively. Kf values for soils with a low organic matter content were lower than that obtained from the only typical allophanic soil derived from volcanic ash under study. Lineal regression analysis between Kf and organic matter content of nonallophanic soils gave a correlation coefficient of 0.980 (P = 0.02). Dispersion of Kd values together with close values of K(OM) indicate that organic matter (OM) was the principal component responsible for MBT adsorption in unamended soils. Addition of peat decreased soil pH and increased adsorption capacity for allophanic and nonallophanic soils. Kinetic experiments showed enhancements of Xmax values and lower rate constants.

Adsorption↗
PubMed2001

Sorption behavior of metolachlor, isoproturon, and terbuthylazine in soils.

The sorption-desorption of metolachlor [2-chloro-N-(ethyl-6-methyl phenyl)-N-(2-methoxy-1-methyl ethyl) acetamide], isoproturon [3-(4-isopropyl phenyl)-1,1-dimethyl urea] and terbuthylazine [N6-tert butyl-6-chloro-N4-ethyl-1,3,5-triazine-2,4-diamine] herbicides was studied in two German soils at 1:10 soil to water ratio by batch method. Equilibrium of herbicides between soil and water (0.01 M CaCl2) was attained in 2 h. Sorption data fitted very well to Freundlich equation, represented by very high correlation coefficient (r2 > 0.934). Comparison of Freundlich K values indicated that sorption of all the three herbicides was most pronounced in soil having higher organic carbon content. Koc values were as expected nearly identical for each herbicide in the two soils. The Freundlich constant (1/n) was about 1 for metolachlor and less than 1 for terbuthylazine and isoproturon indicating a L-type of sorption isotherms. Desorption of all the three herbicides showed hysteresis. Nearly equal amounts of metolachlor, isoproturon and terbuthylazine were desorbed from both soils. There was a good correlation between Koc and solubility.

Acetamides↗
PubMed2001

Isoproturon degradation as affected by the growth of two algal species at different concentrations and pH values.

Metabolism of [14C-u-phenyl]isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] by two soil and freshwater microorganisms, green alga Chlorella kesslerei and cyanobacterium Anabaena inaequalis, was studied as a function of pH, pesticide concentration, and incubation time. Metabolized isoproturon, in the media, ranged from 0% (Chlorella at pH 5.5 after 1 d) to 22% (Anabaena at pH 5.5 after 10 d). Twenty-five percent faster degradation of isoproturon by Anabaena occurred at pH 5.5 versus pH 7.5, when measured over 10 d. Increased 14C incorporation into tissue, with time and at lower pH, was due mainly to bioaccumulation of [14C]isoproturon and/or its metabolites in the cells. Metabolic degradation resulted in four identifiable (by TLC) metabolites. Based on this, a degradation pathway is proposed, involving mono- and di-N-demethylation, hydroxylation of the isopropyl moiety, and hydrolysis to 4-isopropylaniline. Similarity in the metabolites produced suggests that the enzyme systems responsible for metabolizing isoproturon are almost identical in both photosynthetic micro-algae.

Anabaena↗
PubMed2002

Impact of four pesticides on the growth and metabolic activities of two photosynthetic algae.

The acute toxicity was determined for soil algae Chlorella kesslerei and Anabaena inaequalis, exposed to pesticides lindane, pentachlorophenol (PCP), isoproturon (IPU), and methyl parathion (MP). Toxicity markers included growth inhibition, chlorophyll biosynthesis, and total carbohydrate content, as a function of dose and time. Concentration response functions (EC50) were estimated by probit data transformation and weighted linear regression analyses. Lindane's toxicity to Chlorella increased sharply with time (EC50 = 7490, 10.3, 0.09 mg L(-1); 24, 48, 72 h), but remained nearly constant through 72 h with Anabaena (8.7-6.7 mg L(-1); 24-72 h). PCP at low concentrations stimulated algal growth and chlorophyll a production, an effect reversed at higher doses. Anabaena was less tolerant of PCP and MP than was Chlorella. The 96-h static EC50 values for Chlorella were: 0.003, 34, 0.05, and 291 mg L(-1) for lindane, PCP, isoproturon, and MP, respectively; for Anabaena, these were 4.2, 0.13, 0.21, and 19 mg L(-1). Carbohydrate production responses were similar to those of cell density (growth) and chlorophyll biosynthesis, with MP having the lowest adverse impact. The overall relative toxicity among the four tested pesticides was: for Chlorella, lindane > IPU >> PCP >> MP; and for Anabaena, PCP > IPU > lindane > MP. The results confirm that toxicants such as these pesticides may affect individual (though related) species to significantly different degrees.

Anabaena↗
PubMed2003

Isolation and 16S DNA characterization of soil microorganisms from tropical soils capable of utilizing the herbicides hexazinone and tebuthiuron.

Six non-fermentative bacteria were isolated from Colombian (South America) and Hawaiian (USA) soils after enrichment with minimal medium supplemented with two herbicides, hexazinone (Hex) and tebuthiuron (Teb). Microscopic examination and physiological tests were followed by partial 16S DNA sequence analysis, using the first 527 bp of the 16S rRNA gene for bacterial identification. The isolated microorganisms (and in brackets, the herbicide that each degraded) were identified as: from Colombia. Methylobacterium organophilum [Teb], Paenibacillus pabuli [Teb], and Micrmbacterium foliorum [Hex]; and from Hawaii, Methylobacterium radiotolerans [Teb], Paenibacillus illinoisensis [Hex], and Rhodococcus equi [Hex]. The findings further explain how these herbicides, which have potential for illicit coca (Erythroxylum sp.) control, dissipate following their application to tropical soils.

Bacteria↗
PubMed2005

Sorption, degradation, and leaching of tebuthiuron and diuron in soil columns.

A study in small outdoor lysimeters was carried out to determine the leaching of the herbicides tebuthiuron and diuron in different soil types, using undisturbed soil columns. Soil sorption and degradation for both herbicides were also studied in the laboratory. The multi-layered AF (Attenuation Factor) model was evaluated for predicting the herbicides leaching in undisturbed soil columns. Tebuthiuron leached in greater amounts than diuron in both soils. Sorption was well represented by linear and Freundlich equations, however parameters from the linear equations were used in the AF model. In general, both herbicides presented very low sorption, with diuron presenting lower values of sorption coefficient than tebuthiuron in the two soils. Chromatographic data indicated rapid late degradation of diuron and tebuthiuron in both soil types at two different depths. Simple exponential equation was not able to represent degradation, thus a bi-exponential equation was used, and some model adjusting was needed. Average measured amounts of each herbicide were compared with amounts predicted by the multi-layered-soil AF model. The AF model was able to predict leaching amounts in the sandy soil, especially for diuron, however it did not perform well in the clayey soil.

Adsorption↗
PubMed2005

Deposition and leaching of tebuthiuron on sugar cane straw applied with and without alkyl polyglycoside adjuvant.

A laboratory experiment was carried out aiming to study the effects of an alkyl polyglycoside adjuvant (APG) on deposition and leaching of the herbicide tebuthiuron applied on sugar cane straw. Tebuthiuron, at concentration of 1200 mg L(-1), was applied separately and in tank mix with the APG adjuvant, at concentrations of 0.07 and 0.09% (wt v(-1)), using a spraying volume of 204 L ha(-1). A precipitation equivalent to 20 mm of rain was simulated, 24 h after the applications, to evaluate the herbicide leaching. The quantification of tebuthiuron was carried out by the high performance liquid chromatography (HPLC). It was observed that the addition of APG adjuvant at 0.07% (wt v(-1)) provided an increase of 11.5% in the deposition of tebuthiuron on straw, reduction of 50.4% in the drift of the herbicide and it did not affect significantly the leached amount (68.5%), when compared with the treatment where tebuthiuron was applied alone (70.8%). At the concentration of 0.09% (wt v(-1)), the APG adjuvant caused an increase of 22.7% in the deposition; it reduced the drift of the herbicide by 99.9% and reduced the leached amount by 7.6% thereby increasing the retention of the herbicide by straw.

Chromatography, High Pressure Liquid↗