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PubMed2006

Combined effects of constant versus variable intensity simulated rainfall and reduced tillage management on cotton preemergence herbicide runoff.

Pesticide runoff research relies heavily on rainfall simulation experiments. Most are conducted at a constant intensity, i.e., at a fixed rainfall rate; however, large differences in natural rainfall intensity is common. To assess implications we quantified runoff of two herbicides, fluometuron and pendimethalin, and applied preemergence after planting cotton on Tifton loamy sand. Rainfall at constant and variable intensity patterns representative of late spring thunderstorms in the Atlantic Coastal Plain region of Georgia (USA) were simulated on 6-m2 plots under strip- (ST) and conventional-tillage (CT) management. The variable pattern produced significantly higher runoff rates of both compounds from CT but not ST plots. However, on an event-basis, runoff totals (% applied) were not significantly different, with one exception: fluometuron runoff from CT plots. There was about 25% more fluometuron runoff with the variable versus the constant intensity pattern (P = 0.10). Study results suggest that conduct of simulations using variable intensity storm patterns may provide more representative rainfall simulation-based estimates of pesticide runoff and that the greatest impacts will be observed with CT. The study also found significantly more fluometuron in runoff from ST than CT plots. Further work is needed to determine whether this behavior may be generalized to other active ingredients with similar properties [low K(oc) (organic carbon partition coefficient) approximately 100 mL g(-1); high water solubility approximately 100 mg L(-1)]. If so, it should be considered when making tillage-specific herbicide recommendations to reduce runoff potential.

Agriculture↗
PubMed2003

The influence of lipophilicity and formulation on the distribution of pesticides in laboratory-scale sediment/water systems.

Pesticide reaching surface waters will be sorbed by sediment. This sorption process and the influence of pesticide formulation have been examined at 10 degrees C in small-scale systems having 2-cm depth of sediment and 8-cm overlying water stirred gently. Eight pesticides (triasulfuron, isoproturon, chlorotoluron, phenmedipham, difenoconazole, chlorpyrifos, pendimethalin and permethrin), spanning a range of physicochemical properties, were applied individually to the water. Sorption equilibrium was reached at between 15 and 30 days, the proportion of pesticide then in the sediment ranging from 20% for the acidic and therefore polar triasulfuron to 97% for the lipophilic permethrin; this behaviour was not influenced by formulation. Sorption coefficients measured in batch tests over 2 h gave good estimates of the equilibrium distribution. Some degradation was observed for all compounds over 90 days; for some compounds and formulations, enhanced degradation occurred after 20 to 60 days. It is concluded that lipophilicity is the chief determinant of pesticide distribution in sediment/water systems.

Algorithms↗
PubMed1998

Inhibitors of acyl-CoA:cholesterol O-acyltransferase (ACAT). Part 1: identification and structure-activity relationships of a novel series of substituted N-alkyl-N-biphenylylmethyl-N'-arylureas.

A series of N-alkyl-N-biphenylylmethyl-N'-arylurea and related derivatives represented by 1 have been prepared and evaluated for their ability to inhibit acyl-CoA:cholesterol O-acyltransferase in vitro and to lower plasma cholesterol levels in cholesterol-fed rats in vivo. Linking of two phenyl groups via oxygen and introduction of fluorine at appropriate positions on the biphenyl moiety improved in vitro and in vivo activity. From this series of analogs, compound 40 (FR179254), which had potent in vitro potency (rabbit intestinal microsomes IC50 = 25 nM), showed excellent plasma cholesterol-lowering activity when administered via the diet (ED50 = 0.045 mg/kg). However, the hypocholesterolemic effect of this compound was moderate when dosed by oral gavage in PEG400 as a vehicle (ED50 = 5.3 mg/kg). Modification of the N'-aryl moiety led to the identification of compound 50 (FR182980) which was efficacious in both dosing models (ED50 = 0.034 mg/kg and 0.11 mg/kg, respectively).

Anilides↗
PubMed1993

Fetotoxic and teratogenic potential of substituted phenylurea herbicide, isoproturon, in rats.

Effect of isoproturon (0.225, 0.45 and 0.90 g/kg/day) administered (po) from day 6 through 15 of gestation was studied on pregnant rats and their offsprings. There were no distinct clinical signs other than dose-related depression and drowsiness of pregnant rats. None of the animals died due to toxicity of isoproturon. At higher doses, decreased maternal body weight was observed during the advanced stage of pregnancy. The litter size, fetal weight and crown-rump and transumbilical lengths were decreased. There was increase in fetal resorption frequency and the number of fetuses with stunted growth. The compound had no effect on fetal sex ratio. No major visceral and skeletal malformations were observed. The study indicates fetotoxic potential of the compound.

Abnormalities, Drug-Induced↗
PubMed1981

Correlation between the molecular structure of N-alkylureas and N-alkylthioureas and their teratogenic properties.

Eleven urea compounds were administered individually as a single oral dose to rats either on day 12 or 14 and to mice on day 10 of pregnancy. 1-Methylurea and 1-ethylurea were not teratogenic in either of the animal species. Administration of 1-methylthiourea and 1-ethylthiourea, however, resulted in high incidences of malformations in the rat but not in the mouse fetuses. The types of malformation were similar to those produced by the known teratogen ethylenethiourea. Methylated ureas such as 1,3-dimethylurea, 1,3-dimethylthiourea, 1,1,3,3-tetramethylurea, and 1,1,3,3-tetramethylthiourea were fetotoxic and produced malformations in the tail, palate, or extremities of the surviving rat and/or mouse fetuses. These findings suggest that the teratogenic properties of N-alkylureas can be categorized into two groups, i.e., mono-alkylated thioureas and methylated ureas or thioureas.

Abnormalities, Drug-Induced↗
PubMed1999

Determination photostability of selected agrochemicals in water and soil.

The photolysis of selected pesticides in aqueous solutions has been investigated. The photolysis produced different intermediate substances, which were also found to be soil and microbial degradation products. The phototransformation in the presence of TiO2 and humic substances leads to a disappearance of these compounds. The reaction rate is dependent on the semiconductor oxide and concentration. Photoproducts were isolated and characterized by different spectroscopic methods. Results from this study indicate that degradation products of isoproturon are more toxic on Daphnia magna than on the parent compound.

Animals↗
PubMed1992

Characterization of BIBS 39 and BIBS 222: two new nonpeptide angiotensin II receptor antagonists.

Two new nonpeptide angiotensin II (AII) receptor antagonists, 4'-[(2-n-butyl-6-cyclohexylaminocarbonylamino-benzimidazole-1-yl)- methyl ] biphenyl-2-carboxylic acid (BIBS 39) and 2-n-butyl-1-[4-(6-carboxy-2,5-dichlorobenzoylamino)-benzyl]-6-N- (methylaminocarbonyl)-n-pentylamino-benzimidazole (BIBS 222) were characterized in radioligand binding assays, and in vitro and in vivo experiments. BIBS 39 displaced [125I] AII from its specific binding sites with a K(i) value of 29 +/- 7 nM for the AII subtype I (AT1) receptor and a K(i) value of 480 +/- 110 nM for the AII subtype 2 (AT2) receptor. BIBS 222 showed a K(i) value of 20 +/- 7 nM for the AT1 subtype and a K(i) value of 730 +/- 170 nM for the AT2 subtype. Thus BIBS 39 was 17 times more selective for the AT1 subtype and BIBS 222 37 times. Both compounds were specific for AII receptors as they did not show high affinity for other receptors. BIBS 39 shifted the AII concentration-contractile response curves in isolated rabbit aorta to the right in a parallel fashion. A pA2 value of 8.14 +/- 0.08 and a slope of 1.06 +/- 0.07 were calculated. BIBS 222 caused nonparallel shifts to the right and reduced the maximal response induced by AII by about 25%. A KB value of 9.01 (+/- 3.22) x 10(-8) M was determined. At 10(-5) M, neither compounds altered the contractile responses to noradrenaline and KCl. In pithed rats, BIBS 39 dose dependently shifted the dose-response curve of AII to the right without affecting the maximal response.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin Receptor Antagonists↗
PubMed1980

Aging of soman-inhibited acetylcholinesterase: PH-rate profiles and temperature dependence in absence and in presence of effectors.

The influence of pH and temperature upon the dealkylation (aging) of soman-inhibited acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) was investigated. The pH-rate profile, as measured at 5 degrees C, shows a maximum aging rate at pH 5.0 and indicates the involvement of two ionizable groups with pKa values of 6.0 and 4.5. The pH-rate profile was not changed essentially by the two effector compounds, semicarbazide and HH54. the activation energy of aging at pH 7.0 was determined as to 6.12 x 10(4) J/mol; it was lowered by the accelerator of aging semicarbazide to 5.28 x 10(4) J/mol and increased to 9.42 x 10(4) J/mol by the retarding compound HH54.

Cholinesterase Inhibitors↗
PubMed1994

Effect of various angiotensin receptor antagonists on cardiovascular responses to angiotensin II in pithed rats.

The effects of four nonpeptide angiotensin receptor antagonists, i.e., losartan (AT1) PD123177 (AT2), and 4'-[(2-n-butyl-6-cyclohexylaminocarbonylamino-benzimidazole-1-yl)- methyl]biphenyl-carboxylic acid (BIBS 39; AT1 and AT2), and 2-n-butyl-1-[4-(6-carboxy-2,5-di-chlorbenzoylamino)-benzyl]-6-N- (methylaminocarbonyl)-n-pentylamino-benzimidazole (BIBS 222; AT1 and AT2) on cardiovascular responses to angiotensin II (AII) were investigated in propranolol-pretreated pithed rats. AII (0.01-10 nmol/kg intravenously, i.v.) induced a dose-dependent increase in diastolic blood pressure (DBP), the rate of increase in left ventricular pressure (LVdP/dtmax), cardiac output (CO), and total peripheral resistance (TPR) without changing LV end-diastolic pressure (LVEDP) or heart rate (HR). Losartan 3 and 10 mg/kg i.v. caused dose-dependent parallel rightward shifts of the dose-response curves (DBP and LVdP/dtmax) without altering the maximal responses to AII. PD123177 (100 mg/kg i.v.) did not influence the dose-response curves for AII significantly. BIBS 39 (1, 3, and 10 mg/kg i.v.) and BIBS 222 (1, 3, and 10 mg/kg, i.v.) shifted the dose-response curves (DBP and LVdP/dtmax) for AII to the right. Although these two compounds (BIBS 39 1, 3, and 10 mg/kg and BIBS 222 1 and 3 mg/kg) did not alter the maximal increase in DBP to angiotensin AII, they decreased the maximal increase in LVdP/dtmax by approximately 35%. BIBS 39 (3 and 10 mg/kg) significantly reduced the increase in CO caused by AII and therefore mean arterial pressure (MAP), whereas the AII-induced increase in TPR remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗
PubMed1995

Hemodynamic effects of angiotensin II and the influence of angiotensin receptor antagonists in pithed rabbits.

We investigated the cardiovascular effects of angiotensin II (AII) and the influences of four angiotensin receptor antagonists: losartan, PD123177, BIBS 39, and BIBS 222 in the pithed rabbit preparation. AII (0.03-10 nmol/kg) elicited a dose-dependent increase in blood pressure (BP), left ventricular pressure (LVP), LV end-diastolic pressure (LVEDP), dP/dtmax, and heart rate (HR). The maximal hypertensive effect of AII is comparable to that of norepinephrine (NE), but its effects on LVEDP and HR are weaker than those of NE. On a molar base, AII is approximately 27 times more potent than NE. Propranolol (0.5 mg/kg i.v.) did not significantly influence the AII-induced increase in diastolic BP (DBP) and LVEDP, but it abolished AII-induced positive chronotropic effects over the entire dose range of angiotensin AII studied. Losartan, but not PD123177, shifted the dose-response curves for AII to the right in a parallel manner. BIBS 39 and BIBS 222 also caused rightward shifts of the AII dose-response curve. These experiments indicate that in propranolol-treated pithed rabbits AII causes vasoconstrictor effects in both resistance vessels and in the venous system, which are both mediated by AT1- but not by AT2-receptors. The AII-induced positive chronotropic effect is an indirect action mediated by the stimulation of postsynaptic beta 1-adrenoceptors. BIBS 39 and BIBS 222, two new nonpeptide angiotensin receptor blockers that have affinity for both AT1- and AT2-receptors are also potent antagonists of the cardiovascular effects of AII in pithed rabbits.

Analysis of Variance↗
PubMed1987

Aged and bound herbicide residues in soil and their bioavailability. Part 2: Uptake of aged and non-extractable (bound) [carbonyl-14C]methabenzthiazuron residues by maize.

[Carbonyl-14C]methabenzthiazuron (MBT) was applied to growing winter wheat in an outdoor lysimeter. The amount applied corresponded to 4 kg Tribunil/ha. 140 days after application the 0-2.5 cm soil layer was removed from the lysimeter. This soil contained about 40% of the applied radioactivity. Using 0,01 M CaCl2 solution or organic solvents, the extractable residues were removed from the soil. The bioavailability of the non-extractable as well as aged residues remaining in the soil was investigated in standardized microecosystems containing 1.5 kg of dry soil. During a 4 weeks period the total uptake (4 maize plants/pot) amounted up to 3.6; 2.2; and 0.9% of the radioactivity from soils containing aged MBT residues, MBT residues non-extractable with 0.01 M CaCl2 or MBT residues non-extractable with organic solvents, respectively. About 20% of the radioactivity found in maize leaves represented chromatographically characterized parent compound. At the end of the plant experiment the soil was extracted again with 0.01 M CaCl2 and with organic solvents. The soil extracts and also the organic phases obtained from the aqueous fulvic acid solution contained unchanged parent compound.

Benzothiazoles↗
PubMed1991

Eugenol causes oxidant-mediated edema in isolated perfused rabbit lungs.

Eugenol, an extract of cloves, has been associated with pulmonary edema when inhaled from commercially available clove cigarettes. We tested the hypothesis that eugenol directly causes lung edema through oxidant-mediated mechanisms by infusing eugenol (0.1 and 1.0 mM) into isolated rabbit lungs perfused with a cell-free albumin and physiologic salt solution. We observed lung edema (1.0 mM) as demonstrated by increased lung weight gain and wet-to-dry lung weight ratios without alterations in mean pulmonary artery pressure. The oxygen metabolite scavengers catalase (1,000 U/ml) and dimethylthiourea (30 mM) attenuated lung edema. Instillation of dimethylurea, superoxide dismutase, or heat-inactivated catalase did not prevent lung edema formation. We conclude that eugenol causes lung edema in isolated lungs through oxidant-mediated mechanisms in the absence of circulating formed blood elements. Eugenol may be a valuable compound in the laboratory investigation of edemogenic disorders.

Animals↗
PubMed2002

Effect of cropping cycles and repeated herbicide applications on the degradation of diclofop-methyl, bentazone, diuron, isoproturon and pendimethalin in soil.

A greenhouse study was conducted to investigate the ability of four crops (wheat, corn, oilseed rape and soybean) to influence the degradation of bentazone, diclofop-methyl, diuron, isoproturon and pendimethalin in soil. The present study showed that microbial biomass-carbon was significantly higher in planted soils than in bulk soil, especially with wheat and corn, after several cropping cycles. The biomass in corn and soybean planted soils was adversely affected by bentazone but recovered after three cropping cycles. In wheat-planted soils, diclofop-methyl application resulted in persistent increase of the amount of microbial biomass. Bentazone did not show accelerated degradation even after five successive treatments, differing from diclofop-methyl, for which two applications were sufficient to enhance significantly its rate of degradation. Enhanced degradation of diclofop-methyl was even more pronounced in wheat-planted soil. The rates of mineralisation of diuron, isoproturon and pendimethalin were not affected after the first cropping cycle, but were significantly increased in planted soils after five cropping cycles. The results confirm that plants may promote pesticide degradation in soil by stimulating biodegradation processes. In the case of diclofop-methyl, stimulation of accelerated degradation was observed.

Agriculture↗
PubMed1993

Haemotoxic effect of phenylurea herbicides in rats: role of haemoglobin-adduct formation in splenic toxicity.

Three substituted phenylurea herbicides were used for the study of the haemotoxic effects on rats of chronic exposure to these compounds. Female Sprague-Dawley rats were given monuron, diuron or fenuron (250-1000 mg/kg diet) for 14 months. The final body weights were similar to those of controls. No treatment-related effects on organ weights were observed at autopsy, except for a dose-related increase in spleen weights in rats treated with monuron or diuron, but not in those treated with fenuron. The proportion of haemoglobin in the form of methaemoglobin increased in the dosed group and resulted in a secondary anaemia with changes in the morphology of erythrocytes. Haemoglobin adducts of aromatic amines released from the herbicides were present at dose-related levels in rats treated with monuron or diuron. Compound-related lesions were observed histologically in treated rats, with increased pigmentation (haemosiderin) in the spleen, reflecting the response to the haemolytic anaemia and methaemoglobinaemia induced by the herbicides. Pigment deposition consisting of golden brown granules in the cytoplasm of the tubular epithelium in the kidney and in the Kupffer cells in the liver were observed only in rats treated with monuron. The haemotoxic effects that were observed may indicate that the formation of adducts between haemoglobin and the parent aromatic amines released metabolically from these herbicides has a role in the splenic toxicity of these compounds.

Animals↗
PubMed1991

Environmental mutagens that induce the adaptive response to alkylating agents in Escherichia coli.

Many microorganisms exhibit an adaptive response to mutagenic alkylation damage. In Escherichia coli the response is regulated by the inducible Ada protein. A sensitive immunoassay employing two anti-Ada monoclonal antibodies has been developed here to monitor low levels of induction of the Ada protein. This protein was detected in non-induced E. coli which contained an average of two molecules of Ada per cell. The occurrence of the adaptive response in bacteria signals the existence of an ecological niche in which cells are exposed to direct-acting methylating compounds, but the structure and identity of these agents are unknown. Using the immunoassay to search for possible candidates, a number of methylating agents and precursors of such agents have been investigated. Carbamyl phosphate and methylamine yield N-methylurea, which reacts subsequently with nitrite to generate the strong inducer N-methyl-N-nitrosourea. The antibiotic streptozotocin also is a potent inducer of the adaptive response. Moreover, the abundant environmental mutagen methyl chloride acts as an inducer.

Adaptation, Physiological↗