Dichloroacetamide herbicide antidotes enhance sulfate metabolism in corn roots

The herbicide antidotes N,N-diallyl-2,2-dichloroacetamide (R25788) and 3-dichloroacetyl-2,2,5-trimethyloxazolidine (R29148) at ppm levels slightly enhance the uptake of [³⁵S]sulfate in corn roots and greatly increase its metabolism to “bound sulfide”, cysteine, and glutathione (GSH). The decrease in free sulfate content of the roots with R25788 is closely associated with an increase in GSH level. The sulfate content is decreased with an 8-hr exposure to R25788 and R29148 at 3 ppm and its decline continues through 48 hr to about 5% of the control level. Effects on sulfate content are evident at 24 hr even with 0.3–1 ppm of these antidotes. Several other mono- or dichloroacetamide antidotes at 30 ppm also decrease the free sulfate content of corn roots to about 34–60% of control levels within 24 hr. R25788 at 30 ppm has little or no effect at 24 hr on sulfate levels in corn leaves whether the plants are grown in the light or in the dark. R25788 and R29148 decrease sulfate levels in the leaves of milo and in whole pigweed plants, but not in barley, lambsquarters, water grass, wheat, or wild mustard. In increasing GSH biosynthesis, the antidote acts in corn prior to the reduction step to form bound sulfide; in fact, R25788 increases the specific activity of ATP sulfurylase, the first enzyme involved in sulfate assimilation. Thus, dichloroacetamides such as R25788 and R29148 provide a means to experimentally, and perhaps even practically, manipulate sulfate utilization in corn and some other plants.     

Effects of herbicides and herbicide analogs on [14C]leucine incorporation by suspension-cultured Solanum nigrum cells

Assays of [¹⁴C]leucine incorporation were used to measure effects of herbicides on suspensioncultured heterotrophic Solanum nigrum cells. Most herbicidal vs. nonherbicidal chemicals in a set of 47 compounds could be distinguished from each other based on their extent of inhibition of leucine incorporation by S. nigrum cells. Herbicides which failed to inhibit leucine incorporation were photosynthetic inhibitors. Both phytotoxic and nonphytotoxic thiocarbamate analogs (as determined by whole-plant studies) tended to inhibit leucine incorporation. It was concluded that the leucine incorporation screen could detect a majority of compounds tested which are herbicidal, and that it may also be useful to detect compounds which have cellular toxicity which is not observed in the whole plant.     

Quantitative structure-activity studies of substituted benzyl chrysanthemates: 5. Physicochemical substituent factors and neurophysiological effects in knockdown and lethal activities against the house fly

Knockdown and lethal activities of meta- and para-substituted benzyl (1R)-trans-chrysanthemates against the house fly were measured under synergistic conditions using piperonyl butoxide as an inhibitor of oxidative metabolism and NIA 16388 as an inhibitor of hydrolytic degradation. The variations in these activities were quantitatively analyzed in terms of physicochemical substituent effects using electronic, hydrophobic, and steric parameters of the aromatic substituents, and regression analysis. The most significant parameter in determining these activities is the steric bulkiness represented by the van der Waals voluem, the effect of which is highly specific to substituent positions. The substituent effects on knockdown and lethal activities against the house fly are shown to correspond well, respectively, with those on the convulsive and lethal activities against the American cockroach. The relationship between these symptomatic activities against the house fly and the neurophysiological activities determined by using excised nerve cords from American cockroaches were also quantitatively analyzed. Each house fly symptomatic activity was found to be analyzable by a linear combination of the neuroexcitatory and neuroblocking activity indices when the transport factor was separated by using the hydrophobicity parameter.     

Quantitative structure-activity studies of substituted benzyl chrysanthemates: 4. Physicochemical properties and the rate of progress of the knockdown symptom induced in house flies

A procedure to evaluate the knockdown activity of pyrethroids against house flies in which metabolic factors could be eliminated as far as possible was established. With piperonyl butoxide and NIA 16388 as the inhibitors of oxidative and hydrolytic metabolism, respectively, the “intrinsic” knockdown potencies of 22 substituted benzyl (1R)-trans-chrysanthemates and related compounds were determined 2.5–3 hr after topical application to house flies. From the intrinsic knockdown potency and the rate of progress of the knockdown symptom from the earliest stage of intoxication, a “penetration” rate constant was estimated by first-order kinetics using a two-compartment model. The rate constant was correlated quantitatively with the hydrophobic parameter of the molecule. The lower the hydrophobicity, the higher the rate constant within the range of compounds used in this study.     

Comparative ester hydrolysis of carbaryl and ethiofencarb in four mammalian species

The comparative ester hydrolysis and selective toxicity of carbamate insecticides were studied in four mammalian species. Hydrolysis rates of carbaryl and ethiofencarb (Croneton) were examined in the rat, mouse, guinea pig, and gerbil. Respiratory ¹⁴CO₂ resulting from the hydrolysis of orally administered [carbonyl-¹⁴C]carbamates (0.2 mg/kg) was taken as measure of in vivo hydrolytic capabilities. Ester hydrolysis was found to be greater for ethiofencarb than for carbaryl in all species tested, although the relative order of hydrolysis among species was the same with both compounds. After 24 hr, gerbils had hydrolyzed 91% of the ethiofencarb and 65% of the carbaryl. Guinea pigs hydrolyzed somewhat less of the compounds, 65 and 58%, but considerably more than rats and mice, about 40 and 25%. Comparing hydrolysis capabilities to acute toxicity data revealed that those species exhibiting the greatest hydrolysis were equally or more susceptible to carbamate poisoning than those having lesser hydrolytic capabilities. While ester hydrolysis destroys the anticholinesterase activity of carbamates, it is clear from these findings that factors other than hydrolysis are largely responsible for the variation in toxicity of the carbamates to different mammalian species.     

Correlation of blood and brain levels of the neurotoxic pyrethroid deltamethrin with the onset of symptoms in rats

Rats were injected intraperitoneally with ¹⁴C-labelled deltamethrin at the threshold doses required to produce the motor symptoms of toxicity of tremor and choreoathetosis. Blood and brain samples were analysed for their total radiolabel content, and were also extracted with ethyl acetate to determine the levels of extractable parent deltamethrin and 3-phenoxybenzyl-derived acid (the final radiolabelled metabolite after oxidative cleavage) and the residual radiolabel after this extraction. There was a clear correlation between symptom onset and blood and brain levels of deltamethrin. It was found that certain threshold levels of parent deltamethrin in the blood and brain were required for symptom development, and that the symptom persisted for as long as this threshold was maintained. The distribution of the radiolabel in various tissues was also followed over the time course of the blood and brain studies.     

Effect of parathion on renal water and electrolyte excretion in the dog

The effect of a single low dose of parathion on renal water and electrolyte excretion was studied in anesthetized mongrel dogs. Sodium excretion significantly increased 20 min after iv administration of 1.5 μg parathion/kg body wt, while urine output slightly increased and potassium excretion significantly decreased. No change was observed in glomerular filtration rate, renal plasma flow, filtration fraction, and plasma sodium concentration. Respiratory frequency, heart rate, and arterial blood pressure remained unchanged throughout the experiments. With the doses used, no inhibition of acetylcholinesterase in red blood cells or renal tissues was found. The administration of a single dose of 1 μg atropine sulfate/kg body wt iv had no effect in all the parameters measured but was able to completely block the natriuretic effect of parathion when given ten minutes prior to parathion. Since the dose used showed no inhibitory effect on acetylcholinesterase, it is unlikely that the natriuretic effect of parathion could be due to changes in enzyme activity but rather to conformational changes in tubular membranes altering sodium reabsorption.     

Metabolic fate of [14C]endrin in bluegill fish

Bluegill absorbed 85% of 1 ppb of endrin from water within 48 hr under static exposure conditions. The absorbed radiocarbon was eliminated linearly with a half-life of about 4 weeks. Analyses of eliminated radioactivity revealed only conjugated metabolites. 12-anti-Hydroxyendrin and 12-syn-hydroxyendrin were tentatively identified by cochromatography using thin-layer chromatography/autoradiography and gas chromatography. These metabolites were also present as conjugates in the fish organs. Seventy-three percent of the absorbed radioactivity recovered from fish extracts was in the form of unchanged endrin.     

Sulfonylurea herbicides: Growth inhibition in soybean cell suspension cultures and in bacteria correlated with block in biosynthesis of valine,leucine, or isoleucine

The sulfonylurea herbicides chlorsulfuron (CS) and sulfometuron methyl (SM) inhibit the growth of soybean cells (Glycine max L. var. Amsoy 71) in suspension culture with 50% inhibition at 170 and 62 ppb, respectively, relative to the initial cell dry weight, and CS is not rapidly metabolized in these cultures. In Glycine max L. cv Merrill var. Mandarin, CS inhibits the growth by 50% at 4 ppm on the basis of initial cell dry weight. This inhibition is partially reversed by valine, leucine, or 2-ketoisovalerate, but not by pyruvate, isoleucine, or any other single amino acid. CS drastically reduces the content of free valine and leucine in soybean cells without significant effect on the amount of other free amino acids. Deoxyribonucleosides alleviate a portion of the CS growth inhibition in soybean cells in vivo, though CS and SM do not inhibit ribonucleoside diphosphate reductase in vitro. CS and SM are bacteriostats for Escherichia coli and Salmonella typhimurium in minimal growth medium. E. coli growth is retarded at CS concentrations (100–300 μg/ml) that inhibit RNA and protein synthesis but not DNA synthesis. CS growth inhibition in E. coli is enhanced by cysteine and valine and partially alleviated by isoleucine and the aromatic amino acids, but not by leucine. The sulfonylureas appear to act in soybean by blocking the synthesis of valine and leucine between pyruvate and 2-ketoisovalerate and in E. coli by inhibiting isoleucine biosynthesis.     

Activation of an O-ethyl S-n-propyl phosphorothiolate,TIA-230, in the central nerve of Spodoptera larvae

TIA-230, O-[1-(4-chlorophenyl)-4-pyrazolyl] O-ethyl S-propyl phosphorothiolate, showed strong insecticidal activity against Spodoptera larvae, in spite of its weak in vitro anti-AChE activity. Head AChE of Spodoptera was, however, inhibited with the progress of TIA-230 intoxication. When the isolated central nerve cord was incubated with TIA-230, AChE in the tissue was strongly inhibited even by concentration (10^?5M) lower than in vitro I₅₀ against AChE (10^?4M). The frequency of spontaneous firing of the nerve cord was increased by treatment of TIA-230 at low concentrations (10^?6–10^?5M) after a latent time of several minutes. The firing was increased by fenitroxon, but without the latent time. The length of the latent time agreed well with the time necessary for rising the inhibition of nerve cord AChE by TIA-230. AChE inhibition of TIA-230 in the nerve cord was reduced by the treatment of piperonyl butoxide, an inhibitor of mixed-function oxidases. From these results, TIA-230 was regarded as being activated oxidatively in the nerve cord to inhibit AChE. Profenofos was also activated in the nerve cord. It was concluded, therefore, that O-ethyl S-n-propyl phosphorothiolate insecticides were activated in the central nerve of the insect.     

Metabolism of the methoxychlor isostere,dianisylneopentane, in mouse,insects, and a model ecosystem

Dianisylneopentane or 1,1-bis(p-methoxyphenyl)-2,2-dimethylpropane was metabolized largely by O-demethylation to form mono- and diphenol derivatives. Only a small percentage was degraded by α-hydroxylation and rearrangement. In the model ecosystem, dianisylneopentane reacted very similarly to methoxychlor, accumulating in fish to about the same extent and yielding a slightly higher ratio of polar to nonpolar metabolites. The neopentyl group proved to be approximately as stable in biological systems as the isosterically equivalent trichloromethyl group.     

Metabolism and toxicity of metribuzin in mouse liver

Metribuzin was hepatotoxic in mice when administered intraperitoneally (ip) at sublethal doses of 150 to 250 mg/kg. Four dose-dependent abnormalities were evident. Histopathological examination revealed a fulminant centrilobular hepatic necrosis. The serum glutamic-pyruvic transaminase (GPT) activity was elevated. The liver glutathione (GSH) content was almost completely depleted. There was extensive covalent binding of radiocarbon from [carbonyl-¹⁴C]metribuzin to liver proteins and also high blood levels of metribuzin fragments. Each of these four effects of metribuzin on the liver or blood was alleviated or blocked in mice pretreated with piperonyl butoxide (PB), which inhibits the cytochrome P-450-dependent monooxygenase. PB also reduced the lethality of metribuzin by three-fold. In contrast, pretreatment with diethyl maleate to suppress the liver GSH content increased the lethality of metribuzin by twofold. The hepatotoxicity and acute lethality of metribuzin were probably due to reactive intermediates which are normally detoxified by GSH conjugation. The principal urinary metabolites of metribuzin in mice and rats are mercapturic acids, which arise via metribuzin sulfoxide or deaminometribuzin sulfoxide reacting with GSH. Sulfoxidation therefore appears to activate metribuzin to an electrophilic metabolite which, in the absence of GSH, binds to tissue proteins producing hepatotoxicity.     

Comparative metabolism of 1,1-Bis-(p-chlorophenyl)-2-nitropropane (Prolan) in mouse,insects, and in a model ecosystem

¹⁴C-labeled Prolan or 1,1-bis-(p-chlorophenyl)-2-nitropropane was found to be some-what more biodegradable than DDT. This insecticide, although highly resistant to microsomal metabolism, was degraded by elimination to 1,1-bis-(p-chlorophenyl)-1-propene, and by reduction to 1,1-bis-(p-chlorophenyl)-2-aminopropane. The major degradative pathway, however, was by oxidation to 1,1-bis-(p-chlorophenyl)-2-propanone, to 1,1-bis-(p-chlorophenyl)-pyruvic acid, to bis-(p-chlorophenyl)-acetic acid, and ultimately to p,p′-dichlorobenzophenone. Therefore the ultimate degradative products of Prolan are identical to those produced from DDT.     

Muscarinic receptor in house fly brain and its interaction with chlorobenzilate

Membranes from house fly heads were tested for the presence of mucarinic acetylcholine receptors using as a probe [³H]quinuclidinyl benzilate ([³H]QNB). Based on the presence of saturable and reversible high-affinity binding of [³H]QNB, which is inhibited by muscarinic drugs, it is suggested that these sites may be muscarinic receptors. However, these putative muscarinic receptors differ in several characteristics from the ones in mammalian brain. They have lower affinities for muscarinic drugs and lower stereoselectivity, a relatively higher affinity for the nicotinic antagonist d-tubocurarine, a lower Hill coefficient for binding of muscarinic antagonists, and a lower concentration relative to α-bungarotoxin binding sites in the same membranes. Also, unlike mammalian muscarinic receptors, they are sensitive to treatments with N-ethylmaleimide and 5,5′-dithiobis(2-nitrobenzoic acid). The effect of reduction of disulfide bonds by dithiothreitol or mercaptoethanol suggests that only the insect receptor has one or more disulfide bonds which are important to binding. On the other hand, the putative muscarinic receptors of both insect and mammalian brains have important SH group(s), whose alkylation by p-chloromercuribenzoate inhibits binding. Also, chlorobenzilate is equally effective in inhibiting [³H]QNB binding to muscarinic putative receptors of house fly and bovine brains.     

Effects of glyphosate on uptake,translocation, and intracellular localization of metal cations in soybean (Glycine max) seedlings

Root-fed or foliar-applied glyphosate [N-(phosphonomethyl) glycine] reduced uptake and translocation of Ca²⁺ and Mg²⁺, but not K⁺, by soybean [Glycine max (L.) Merr. “Hill”] seedlings as measured by atomic absorption spectrometry. Histochemical techniques revealed that cells of secondary roots that were formed after glyphosate treatment were deficient in Ca²⁺. The relative distribution of Ca²⁺ in control root and leaf cells was mitochondria > plastids > cytoplasm. Glyphosate severely reduced Ca²⁺ content and eliminated intracellular concentration of Ca²⁺ in the mitochondria of both root and leaf cells. Glyphosate had no effects on K⁺ distribution at the ultrastructural level. These results support the view that glyphosate effects on distribution of divalent metal cations may be related directly or indirectly to the phytotoxicity of the herbicide.     

The effect of O,S,S,-trimethyl phosphorodithioate on the in vivo metabolism of phenthoate in the rat

The in vivo metabolism of phenthoate (O,O-dimethyl S-[α-(carboethoxy)benzyl]phosphorodithioate) was followed in rats after oral administration of a nontoxic dose of 100 mg/kg. The same metabolic study was conducted following coadministration of 0.5% O,S,S-trimethyl phosphorodithioate (OSS-Me). When administered alone, phenthoate was metabolized principally by carboethoxy ester hydrolysis and cleavage of the PO and CS bonds, resulting in at least six metabolites. The primary urinary metabolite excreted was phenthoate acid. Coadministration of 0.5% OSS-Me did not alter the types of metabolites excreted. However, a reduction of the carboxylesterase-catalyzed product (phenthoate acid) was observed, indicating that the enzyme responsible for the major pathway of phenthoate detoxication was inhibited. Alternate detoxication processes did not compensate for the reduction in carboxylesterase-catalyzed detoxication. It was concluded that inhibition of the carboxylesterase enzymes is the major cause of the potentiation of phenthoate toxicity by OSS-Me.     

The effect of organophosphorous insecticides upon catecholamine fluorescence in the corpus centrale and frontal ganglion of the house cricket, Acheta domesticus (L.)

Treatment of the house cricket Acheta domesticus (L.) with tetraethyl pyrophosphate and dicrotophos causes a depletion of the catecholamine stores of the central nervous system. Fluorescence microscopy of the brain and frontal ganglion 30 min after knock-down revealed a reduction in the catecholamine-specific fluorescence of the corpus centrale and frontal ganglion neuropile. In the corpus centrale the effect was much more pronounced and less variable with dicrotophos than with tetraethyl pyrophosphate, whereas both compounds appeared to have similar effects on the frontal ganglion. The possible relationship of this depletion to symptoms of intoxication requires further investigation.     

Pharmacokinetics of pyrethroids in twospotted spider mites

The penetration and degradation of six pyrethroids were examined in the twospotted spider mite, Tetranychus urticae Koch, and the results were related to their toxicity as measured by inhibition of respiration using the Warburg technique and mortality using the slide-dip bioassay. FMC-54800 [1,1′-biphenyl-3ylmethyl cis-3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclopropanecarboxylate] was the most toxic pyrethroid to the mites based on both respiration and mortality studies. It and flucythrinate had the highest pharmacokinetic efficiency as determined by delivery and maintenance of internal levels of parent compounds. Permethrin, fenvalerate, and fluvalinate were intermediate in pharmacokinetic efficiency, whereas cypermethrin was significantly lower. The highest intrinsic activity, as estimated by the percentage inhibition of respiration per microgram of internal parent, was possessed by cypermethrin and FMC-54800. Fenvalerate and fluvalinate had intermediate levels, while permethrin and flucythrinate had significantly lower capacities to inhibit respiration. The combination of relatively high pharmacokinetic efficiency and intrinsic activity of FMC-54800 appeared to be responsible for its high toxicity. In addition to these findings, differences in the kinetics for cis and trans isomers were observed for permethrin but not cypermethrin. This study has yielded evidence that acaricidal activity of pyrethroids can be enhanced by optimizing the structure for increased pharmacokinetic efficiency and increased intrinsic activity.     

β-d-Glucosyl and O-malonyl-β-d-glucosyl conjugates of pentachlorophenol in soybean and wheat: Identification and enzymatic synthesis

The polar metabolite fraction formed by soybean cell suspension cultures from [¹⁴C]pentachlorophenol (PCP) was fractionated by repeated high-performance liquid chromatography. The β-d-glucopyranosyl conjugate of PCP was identified by cochromatography, by chemical and enzymatic degradation, and by mass spectroscopic comparison with the authentic compound. The O-(malonyl)-β-d-glucopyranosyl conjugate of PCP was identified by chromatographic and electrophoretic comparison with the enzymatically synthesized compound, by specific chemical and enzymatic degradation, and by mass spectroscopy. Soluble protein extracts from both soybean and wheat cells catalyzed (a) the UDPG-dependent conversion of PCP to the β-d-glucopyranosyl conjugate, and (b) the malonyl-SCoA-dependent further conversion to the O-(malonyl)-β-d-glucopyranosyl conjugate. These enzymes were partially purified and had apparent molecular weights between 40,000 and 48,000. Free PCP was again released from the conjugates upon incubation with plant malonyl esterase and/or β-glucosidase preparations.     

Phytotoxicity and metabolism of chlortoluron in two wheat varieties

Varietal susceptibility of winter wheat to chlortoluron, 1-(3-chloro-4-methylphenyl)-3,3 dimethylurea, has been studied in two varieties, Corin (susceptible) and Clement (tolerant). After a 24-hr root absorption of the herbicide, phytotoxicity was estimated from growth measurements. When administered at 12 to 96 μM concentrations, the herbicide reduced the growth of both varieties. A significant selective effect was found at 96 μM. Measurements of chlorophyll fluorescence-induction kinetics allowed to discriminate between the two varieties treated with 12 to 48 μM chlortoluron. The metabolism of chlortoluron was studied following absorption of 24 μM solutions. Both varieties produced the same pattern of metabolites but the tolerant variety degraded the herbicide and the phytotoxic mono-N-demethylated metabolite at a slightly higher rate. An unexpected result was that the more susceptible variety possessed a very significant ability to metabolize chlortoluron. In conclusion, it appears that further studies are necessary before deciding whether the differences in susceptibility of the two varieties can be explained by the only metabolic factor.