Inhibitor Report for: Dichlorvos

Organophosphates are chemicals commonly used as pesticides and work to inhibit acetylcholinesterase, leading to acetylcholine build up at muscarinic and nicotinic receptors throughout the body. Poisonings are often seen as small volume, chronic cases due to agricultural exposures, but can present as suicide attempts via organophosphate ingestion. Organophosphate poisonings, particularly when large volumes are ingested, require rapid and robust initiation of treatment. We present a case highlighting the appropriate management of profound organophosphate toxicity. We present a case of a 40-year-old female brought in by ambulance after purposefully ingesting two bottles of 100mL dichlorvos (DDVP), one of the largest volume organophosphate ingestions documented in the literature. She presented with severe salivation, diaphoresis and encephalopathy and was then intubated, requiring mechanical ventilation. She received multiple days of intensive care as she was treated with atropine, pralidoxime, intravenous fluids and vasopressors.

Out of three most important classes of synthetic insecticides only the carbamates and pyrethroids were known to have ancestors in nature. Now two organophosphates (which are quite good insecticides and very potent acetylcholinesterase inhibitors, e.g. comparable to carbofuran) have been isolated from Streptomyces antibiotices antibioticus strain DSM 1951.

The enzyme butyrylcholinesterase from horse serum catalyses the hydrolysis of certain esters. The orange-red 2,6-dichloroindophenyl acetate will be converted by the enzyme into a deep blue alcohol. The colour transformation does not occur when the enzyme is inactivated. By making use of this biochemical reaction a cheap and simple, but very sensitive and specific detection tube could bedeveloped. The tube comprises a breakable ampoule with an aqueous buffer solution, a freeze-dried preparation of the chromogenic ester with a filler promoting its dissolution, a freeze-dried preparation of butyrylcholinesterase with a filler promoting its stability, and an indication layer. DDVP can be detected at concentrations as low as 0.4 mg/m3, when the sampled airvolume is 21.

Organophosphates are chemicals commonly used as pesticides and work to inhibit acetylcholinesterase, leading to acetylcholine build up at muscarinic and nicotinic receptors throughout the body. Poisonings are often seen as small volume, chronic cases due to agricultural exposures, but can present as suicide attempts via organophosphate ingestion. Organophosphate poisonings, particularly when large volumes are ingested, require rapid and robust initiation of treatment. We present a case highlighting the appropriate management of profound organophosphate toxicity. We present a case of a 40-year-old female brought in by ambulance after purposefully ingesting two bottles of 100mL dichlorvos (DDVP), one of the largest volume organophosphate ingestions documented in the literature. She presented with severe salivation, diaphoresis and encephalopathy and was then intubated, requiring mechanical ventilation. She received multiple days of intensive care as she was treated with atropine, pralidoxime, intravenous fluids and vasopressors.

Acylpeptide hydrolase (APH) unblocks N-acetyl peptides. It is a major serine hydrolase in rat blood, brain, and liver detected by derivatization with (3)H-diisopropyl fluorophosphate (DFP) or a biotinylated fluorophosphonate. Although APH does not appear to be a primary target of acute poisoning by organophosphorus (OP) compounds, the inhibitor specificity of this secondary target is largely unknown. This study fills the gap and emphasizes blood APH as a potential marker of OP exposure. The most potent in vitro inhibitors for human erythrocyte and mouse brain APH are DFP (IC(50) 11-17 nM), chlorpyrifos oxon (IC(50) 21-71 nM), dichlorvos (IC(50) 230-560 nM), naled (IC(50) 370-870 nM), and their analogs with modified alkyl substituents. (3)H-diisopropyl fluorophosphate is a potent inhibitor of mouse blood and brain APH in vivo (ED(50) 0.09-0.2 mg/kg and 0.02-0.03 mg/l for ip and vapor exposure, respectively). Mouse blood and brain APH and blood butyrylcholinesterase (BChE) are of similar sensitivity to DFP in vitro and in vivo (ip and vapor exposure), but APH inhibition is much more persistent in vivo (still >80% inhibition after 4 days). The inhibitory potency of OP pesticides in vivo in mice varies from APH selective (dichlorvos, naled, and trichlorfon), to APH and BChE selective (profenofos and tribufos), to ChE selective or nonselective (many commercial insecticides). Sarin administered ip at a lethal dose to guinea pigs inhibits blood acetylcholinesterase and BChE completely but erythrocyte APH only partially. Blood APH activity is therefore a sensitive marker for exposure to some but not all OP pesticides and chemical warfare agents.

The rates of inhibition of mouse acetylcholinesterase (AChE) (EC 3.1.1.7) by paraoxon, haloxon, DDVP, and enantiomers of neutral alkyl methylphosphonyl thioates and cationic alkyl methylphosphonyl thiocholines were measured in the presence and absence of AChE peripheral site inhibitors: gallamine, D-tubocurarine, propidium, atropine and derivatives of coumarin. All ligands, except the coumarins, at submillimolar concentrations enhanced the rates of inhibition by neutral organophosphorus compounds (OPs) while inhibition rates by cationic OPs were slowed down. When peripheral site ligand concentrations extended to millimolar, the extent of the enhancement decreased creating a bell shaped activation profile. Analysis of inhibition by DDVP and haloxon revealed that peripheral site inhibitors increased the second order reaction rates by increasing maximal rates of phosphylation.

To determine the protective effect of pralidoxime on muscle fiber necrosis induced by organophosphate acute intoxication in rats. DESIGN: Adult male Wistar rats were given oral organophosphate compounds dissolved in glycerol formal: dichlorvos, isofenphos, metamidophos, and diazinon. Half of the animals also received pralidoxime mesylate (20 mg/kg, intraperitoneal). Control animals received only the solvent. Twenty-four hours after treatment, the diaphragm muscle was collected for histological counts of necrotic muscle fibers in transverse sections. RESULTS: Metamidophos- and isofenphos-treated animals showed the highest percentage of necrotic muscle fibers: 1.66 +/- 1.112 and 1.34 +/- 0.320, respectively. Diazinon-treated animals had a lower percentage of necrotic fibers: 0.40 +/- 0.032 (p < 0.05) compared to the first 2 products, and dichlorvos-treated animals showed the smallest: 0.05 +/- 0.021 (p < 0.05) when compared to the other 3 products. Pralidoxime reduced necrotic fibers about 20 times in metamidophos-treated animals, 10 times in isofenphos-treated animals and 6 times in diazinon-treated animals. Pralidoxime administration did not increase plasma cholinesterase activity in any group, although symptoms were reduced. CONCLUSIONS: Oxime reduced diaphragmatic muscle necrosis in experimental organophosphate intoxication, despite little effect on plasma cholinesterase. Since respiratory insufficiency is an important cause of mortality and morbidity in organophosphate intoxications, early oxime administration may be particularly beneficial.

Carboxylesterases (CbxE) can be inhibited by organophosphorus esters (OPs) without causing clinical evidence of toxicity. CbxE are thought to protect the critical enzyme acetylcholinesterase (AChE) from OP inhibition in animals. CbxE and AChE are both present in neuroblastoma cells, but, even though these cells have potential to be an in vitro model of OP toxicity, the effect of OPs on CbxE and the relationship of CbxE inhibition and AChE inhibition have not yet been examined in these cells. Therefore, this study examined concentration-related OP-induced inhibition of CbxE in human SH-SY5Y and mouse NB41A3 neuroblastoma cells with 11 active esterase inhibitors: paraoxon, malaoxon, chlorpyrifos-oxon, tolyl saligenin phosphate (TSP), phenyl saligenin phosphate (PSP), diisopropyl phosphorofluoridate (DFP), mipafox, dichlorvos, trichlorfon, dibutyryl dichlorovinyl phosphate (DBVP), and dioctyl dichlorovinyl phosphate (DOVP). All could inhibit CbxE, although the enzyme was less likely to be inhibited than AChE following exposure to 9 of the test compounds in the human cell line and to all 11 of the test compounds in the murine cell line. Species differences in concentration-related inhibitions of CbxE were evident. When cells were exposed first to an OP with a low IC50 toward CbxE (PSP), followed by an OP with high affinity for AChE (paraoxon or malaoxon), inhibitions of CbxE and AChE were additive. This indicated that CbxE did not protect AChE from OP-induced inhibition in this cell culture model.

Alzheimer's disease is a chronic neurodegenerative disorder that is characterized by memory impairment, cognitive dysfunction, behavioral disturbances, and deficits in activities of daily living. A consistent observation in these patients is that cholinergic neurons are affected and deteriorate over time, leading to decreased levels of acetylcholine (ACh). Acetylcholinesterase (AChE) inhibitors, which attempt to prevent the breakdown of ACh, may be classified as short acting, intermediate acting, and long acting based on AChE regeneration time. Metrifonate is converted by a nonenzymatic process to the long-acting cholinesterase inhibitor 2,2-dichlorovinyl dimethyl phosphate (DDVP). Acetylcholinesterase inhibition produced by metrifonate occurs rapidly, is dose dependent, can be detected by inhibition measured in red blood cells, and can be reversed by oxime administration. Metrifonate and DDVP improved performance in young rats; cognitive improvement in aged rats also was observed. Both agents were well tolerated and did not have significant effects on various preclinical pharmacologic safety tests.

Metrifonate is converted nonenzymatically to 2.2, dimethyl dichlorovinyl phosphate (DDVP), an inhibitor of acetylcholinesterase (AChE). This 21-day, randomized, double-blind, placebo-controlled trial of metrifonate in patients with Alzheimer's disease (n = 27) evaluated four doses, each administered orally once daily. All patients received a loading dose (LD) for 6 days followed by a maintenance dose (MD) for 15 days. The treatment groups were: panel 1, LD = 1.5 mg/kg (75-135 mg), MD = 0.25 mg/kg (12.5-25 mg); panel 2, LD = 2.5 mg/kg (125-225 mg), MD = 0.40 mg/kg (20-35 mg); panel 3, LD = 4.0 mg/kg (200-335 mg), MD = 0.65 mg/kg (30-60 mg); and panel 4, LD = 4.0 mg/kg (200-335 mg), MD = 1.0 mg/kg (50-90 mg). All metrifonate doses were well tolerated. Most adverse events were mild to moderate in intensity, gastrointestinal in nature, and transient. Mean area under the concentration-time curve (AUC) and maximum concentration (Cmax) for both metrifonate and DDVP increased in relation to dose. Metrifonate and DDVP had similar, largely dose-independent mean values for time to Cmax (tmax) and half-life (t1/2). There was little or no accumulation of either metrifonate or DDVP with long-term administration. After 21 days of treatment, mean percent erythrocyte AChE inhibition was 14%, 35%, 66%, 77%, and 82% for placebo and panels 1 through 4, respectively. Cognitive improvement was observed with the two highest metrifonate doses. These results reflect favorable safety and pharmacokinetic profiles for the use of metrifonate in the treatment of Alzheimer's disease.

The present study was carried out to assess the biochemical and behavioral sequelae of chronic dichlorvos (6 mg/kg b.wt/day for 8 weeks) exposure in rats. Dichlorvos administration significantly decreased the activities of neuropathy target esterase and other carboxylesterase viz., paraoxon resistant and mipafox and paraoxon resistant esterases. The acetylcholinesterase activity was also appreciably decreased following dichlorvos exposure. The alterations in biochemical parameters were also reflected in the behavioral patterns of dichlorvos-treated animals. Dichlorvos administration caused a marked decrease in both the ambulatory and stereotypic components of spontaneous locomotor activity of rats. The muscle strength and coordination of the dichlorvos-treated animals was also significantly impaired. Besides, a marked deterioration in the memory function assessed in terms of the conditioned avoidance response was discernible at the end of the treatment schedule in the experimental animals.

We reviewed 130 admissions of organophosphate poisoning and analyzed the causes of death. Fenitrothion, malathion, dichlorvos, trichlorfon and fenitrothion/malathion were the most frequent chemicals involved. Mortality was 25% (32/130); delay in discovery and transport (18 cases), insufficient respiratory management (8 cases), and severe underlying or co-existing diseases (6 cases) were noted in the lethalities. Insufficient respiratory management consisted of delay in endotracheal intubation (5 cases) and failure in weaning (3 cases). About 3/4 of the severely serum cholinesterase-depressed cases needed ventilators. This suggests that better respiratory management would improve the outcome of organophosphate poisonings. Close observation of the clinical symptoms is essential, and detection of changes in serum cholinesterase may be helpful.

Tissue distribution of dichlorvos (DDVP) was determined in a case of fatal ingestion using a rapid and simple gas chromatographic (GC) assay. Remarkable autopsy findings were congestion of the lung and kidneys and bleeding ulcer extending from the dorsum of the tongue to the upper pharynx. The serum cholinesterase activity was 2 IU/1, however, miosis was not observed. In the stomach, 250 ml of volatile fluid was found. Tissue distribution of DDVP was determined using a newly developed simple and rapid GC method. DDVP was found in the spleen and heart at higher concentrations (3340 and 815 micrograms/g, respectively), and also detected in the urine at the lowest level (4.5 micrograms/ml). The DDVP concentrations in blood, brain, lung, kidney and liver were 29, 9.7, 81, 80 and 20 micrograms/ml or g, respectively.

Populations of Culex pipiens were sampled from 8 locations in Cyprus between 1987 and 1993. All population samples generally revealed organophosphate resistance to malathion, temephos, chlorpyrifos, fenthion, dichlorvos, and pirimiphos methyl, in decreasing order of magnitude. Of 7 populations assessed with the carbamate propoxur, all proved to be resistant to different degrees. Of the 6 populations tested with permethrin, 2 were resistant to permethrin. Resistance was associated with the presence of 5 different overproduced esterases (esterases A1, A2, A5, B2, and B5) as well as an insensitive form of acetylcholinesterase. These results are discussed in relation to the ongoing mosquito abatement program in Cyprus and to similar programs in other parts of the world.

Dichlorvos (DDVP)-induced DNA single strand breaks were investigated in isolated rat hepatocytes. In a dose-response study in hepatocytes from PB-treated rats (80 mg/kg i.p., for 3 days), 250 microM DDVP substantially reduced cellular non-protein sulfhydryl (NPSH) content, but had no detectable effect on DNA. At 500 microM, the increase in DNA single strand breaks was significant, with a slight increase in cellular lipid peroxidation. At doses over 1000 microM DDVP, cell death was accompanied with considerable lipid peroxidation, and DNA single strand breaks were evident. When the antioxidant N,N'-diphenyl-p-phenylene diamine (DPPD) was added or if the hepatocytes were incubated under air instead of 95% O2, lipid peroxidation and cell death were attenuated but DNA single strand breaks and reduction in NPSH content were not. On the other hand, ferrous iron-induced DNA single strand breaks, lipid peroxidation, and depletion of NPSH content were all attenuated by DPPD or by incubating the cells under air. With respect to the subcellular lipid peroxidation, DDVP caused a significant increase mainly in the microsomal fraction, whereas ferrous iron caused rapid and substantial increases in mitochondrial, microsomal, and nuclear fractions. There were more DNA single strand breaks caused by N-nitrosodiethylamine (NDEA), which becomes genotoxic after microsomal metabolism, in hepatocytes from PB-treated rats than in those from control rats. The number of these breaks was reduced by adding the cytochrome P450 inhibitor metyrapone. On the other hand, the effect of DDVP on DNA was not affected by modification of the cytochrome P450 status. These results suggest that lipid peroxidation induced by DDVP in isolated rat hepatocytes plays a significant role in its cytotoxicity but not in its genotoxicity.

Wistar rats were exposed to dichlorvos [CAS number 62737]. Doses were 1/25; 1/50; and 1/100 LD50, that is 3.88; 1.94; 1.46; and 0.97 mg kg-1 DDVP, respectively, throughout gestation (GD1-birth) and during suckling via oral dosing to the dams, and then via the same doses by gavage for the rest of their lives. The offspring were tested in an open field (OF), a multiple T-maze, and in a 'novelty-induced-grooming' test to assess behavioural competence as adults. Dose-related increases in running time and incorrect choices in the maze were observed during the first 2 weeks of a 3-week study at 9-11 weeks of age. Horizontal activity was increased, vertical activity decreased, and defecation decreased in the OF at 9-12 weeks of age; these changes were again dose-related. Sleep was also affected at 12 weeks of age. AChE activity in the brain and in blood at sacrifice was roughly 40% to 65% of control, again reflecting the doses administered. The significantly changed behavioural profile of DDVP treated rats may serve as a useful biomarker to judge functional damage of CNS properties.

Acute organophosphorus insecticides poisoning (AOIP) is a common medical emergency. There is, at present, a tendency to use high-dose atropine treatment (HDAT). This study aims to test if, during AOIP, HDAT would cause upregulation of muscarinic receptor (M-R). Male mice of the same batch and strain were raised, randomly divided into 3 groups and orally fed with DDVP of the same dose. HDAT for 7 days was given to group A, HDAT for 36 hours was given to group B and low-dose atropine treatment for 36 hours was given to group C. Then radionuclide assay was employed to measure the M-R in the brain and atrium of the mice in each group. The results were that, compared with a control group, the Bmax values (fmol.mg protein-1) of M-R in groups A and B were increased significantly (P < 0.01), while that in group C showed no evident change (P > 0.05). These results indicate that HDAT leads to some physiological change in the body, which may be responsible for the development of poisoning rebound and atropine dependence.

We studied the pharmacokinetics and pharmacodynamics [red blood cell (RBC) cholinesterase (ChE) inhibition] of metrifonate (MTF) and its active anti-ChE metabolite, dichlorvos (DDVP) in Alzheimer's disease (AD) patients and normal controls after oral MTF. In Study I conducted for 6 h, 3 patients with prior MTF exposure received oral MTF (7.5 mg/kg). Plasma ChE inhibition peaked to 78.5 +/- 12.3% at 15 min, while maximum RBC ChE inhibition seen at 1 h was 61.0 +/- 11.0%. Plasma ChE inhibition was unchanged at 6 h, whereas RBC ChE recovered with a t1/2 of 7.0 +/- 3.5 h. In Study II, 6 patients and 6 controls with no prior MTF exposure were given oral MTF. Mean plasma t1/2 of MTF was 2.3 +/- 0.3 h with ChE recovery t1/2 of 9.0 +/- 3.3 (plasma) and 26.6 +/- 15.2 days (RBC) after 7.5 mg/kg MTF. The short drug t1/2, long ChE recovery t1/2 and the achievement of high ChE inhibition levels with minimal side effects suggest the potential use of this drug for Alzheimer therapy.

Adult bedbugs, Cimex lectularius, were exposed for 24 h (25 degrees C) to filter paper treated with various dilutions of the technical grade of nine insecticides dissolved in acetone to determine the concentration-response relationships. The order of toxicity, from most to least based on the LC50's was: dichlorvos, pirimiphos methyl, lambda-cyhalothrin, bendiocarb, permethrin, malathion, carbaryl, tetrachlorvinphos, and fenvalerate. The residual toxicities of commercial formulations of six of the chemicals diluted with water and applied to wood, cardboard, cloth and galvanized metal, were determined by exposing adult bedbugs at 3, 7 and 12 weeks after treatment. The formulation of bendiocarb (FICAM 76% W) had little residual activity on all surfaces at 12 weeks after treatment. The formulation of carbaryl (SEVIN 21.5% L) was toxic to bedbugs on all surfaces at 12 weeks after treatment, but required high concentrations on wood, cardboard, and cloth. The formulation of pirimiphos methyl (ACTELLIC 57% EC) had no residual activity on any of the surfaces at 12 weeks after treatment. The formulation of tetrachlorovinphos (RABON 50% W) had residual activity for 12 weeks on all surfaces except metal. The formulation of permethrin (ATROBAN 11% EC) had residual activity on only metal and wood while the formulation of lambda-cyhalothrin (KARATE 13.1% EC) had residual activity 12 weeks on all surfaces.

Dichlorvos (DDVP) is used as an antihelmetic, principally in dogs, cats, pigs and horses. Retina, whole blood, erythrocyte, plasma and brain cholinesterase (ChE) activities were monitored following DDVP exposure in cats to establish their use as indicators of exposure to a ChE inhibitor. Following DDVP exposure, whole blood ChE activity was 16.8% of preexposure, erythrocyte ChE activity was 33% of preexposure, and plasma ChE was 19% of preexposure values. Brain and retinal ChE activities were reduced to 45% and 43% of control values. Retinal ChE paralleled brain activity.

Transdermal delivery of cholinesterase inhibitors (ChEI) for treatment of dementia would have advantages associated with continuous dosing and enhanced compliance, but feasibility depends on achieving desired levels of central nervous system enzyme inhibition. We developed a patch technique for assessing delivery of ChEI in rats and examined two organophosphate compounds, metrifonate and DDVP, and a carbamate, heptylphysostigmine, for production of peripheral and central nervous system ChE inhibition at target levels. With DDVP, a log-dose/percent brain AChE inhibition was obtained over a range of 10-65% inhibition within a 10-fold concentration of inhibitor in the patch. Brain cholinesterase was inhibited up to seven days after a 24-h patch application. Long-term inhibition was greater than that attained after intramuscular injection, but without the rapid initial inhibition peak seen with the latter route. In contrast to DDVP, sustained high levels of brain enzyme inhibition could not be produced by transdermal delivery of metrifonate or heptylphysostigmine. Apparently DDVP has features, i.e., liquid state in pure form and high inhibitor potency, which make it particularly suitable for patch administration.

A flow injection system, incorporating an acetylcholinesterase (AChE) single bead string reactor (SBSR), for the determination of some organophosphorous (azinphos-ethyl, azinphos-methyl, bromophos-methyl, dichlorovos, fenitrothion, malathion, paraoxon, parathion-ethyl and parathion-methyl) and carbamate insecticides (carbofuran and carbaryl) is presented. The detector is a simple pH electrode with a wall-jet entry. Variations in enzyme activity due to inhibition are measured from pH changes when the substrate (acetylcholine) is injected before and after the passage of the solution containing the insecticide. The percentage inhibition of enzyme activity is correlated to the insecticide concentration. Several parameters influencing the performance of the system are studied and discussed. The detection limits of the insecticides ranged from 0.5 to 275 ppb. The determination of these compounds was conducted in Hepes buffer and a synthetic sea water preparation. The enzyme reactor can be regenerated after inhibition with a dilute solution of 2-PAM and be reused for analysis. The immobilized enzyme did not lose any activity up to 12 weeks when stored at 4 degrees C.

2,3-Butanedione monoxime and atropine alone or in combination were evaluated for their ability to alleviate the toxicity and to reverse the biochemical changes induced by dichlorvos in the blood of buffalo calves. Treatment with 2,3-butanedione monoxime plus atropine 30 min after oral administration of dichlorvos (160 mg/kg) eliminated the apparent toxic signs within 10-15 min, completely prevented lethality, and reversed the dichlorvos-induced alterations in the concentrations of serum carboxylesterase, total plasma proteins, blood glucose and plasma cholinesterase within 2, 4, 12 and 168 h, respectively. Treatment with either 2,3-butanedione monoxime or atropine alone was less effective but the former was the more potent of the two in counteracting the biochemical effects of dichlorvos. These antidotal studies suggest that 2,3-butanedione monoxime in conjunction with atropine would provide effective therapy against severe dichlorvos intoxication in buffalo.

Zinc chloride-diphenylamine reagent, whose use has been reported for the detection of organochlorine insecticides by thin layer chromatography, was further studied for its ability to detect the organophosphorus insecticides phorate, phosphamidon, DDVP, and phosalone and the carbamate insecticide carbaryl and aldicarb. These insecticides give intense blue-green spots with this reagent. The procedure can be applied to the detection of the insecticides in biological materials and thus has a potential use in forensic toxicology.

Catalytic properties of human blood erythrocyte acetylcholinesterase and horse blood serum butyrylcholinesterase immobilized and nonimmobilized in the gelatin membrane have been comparatively studied. Cholinesterase immobilization induces an increase in the Michaelis constant value and a decrease in the maximum rate value in reactions of enzymic hydrolysis of thiocholine ethers, but exerts no effect on these kinetic parameters in case of enzymic hydrolysis of indophenylacetate. The effect of reversible inhibitors: galanthamine, N-methyl-4-piperidinyl benzylate and 1,2,3,4-tetrahydro-9-aminoacridine (tacrine), as well as of irreversible inhibitors: O-ethyl-O-(4-nitrophenyl)ethyl phosphonate (armin), diisopropyl fluorophosphate (DFP), O,O-diethyl-O-(4-nitrophenyl) phosphate (paraoxon) and O,O-dimethyl-O-(2,2-dichlorovinyl) phosphate (DDVP) on immobilized cholinesterases is weaker as compared with the effect on nonimmobilized enzymes. The results obtained are discussed for the effect of immobilization on the catalytically active enzyme surface.

Responses of Paramecium caudatum, a ciliated protozoan, to acute exposures of certain organic solvents and organophosphorus insecticides (OPI) were studied by determining their lethal concentration (10 min-LC100) and median lethal concentration (4 h-LC50). The solvents and OPI evoked a distinct sequence of responses. Among the five solvents tested, acetone proved most toxic [LC-2.9% and LC50-0.68% (v/v)], while dimethyl sulphoxide (DMSO) showed least toxicity [LC-11.0% and LC50-3.16% (v/v)]. The order of toxicity of solvents was: acetone greater than ethanol greater than methanol greater than N, N-dimethylformamide greater than dimethylsulphoxide. The LC values of six OPI dissolved in either acetone or DMSO indicated that they were more toxic when dissolved in acetone and least toxic in DMSO. Among the OPI, bromophos proved most toxic (LC-10 ppm) while malathion showed least toxicity (LC-200 ppm) in DMSO. The order of toxicity of OPI was: bromophos greater than pirimiphos-methyl greater than parathion methyl greater than dichlorvos greater than fenitrothion greater than malathion. The 4 h-LC50 values computed for bromophos and malathion (dissolved in DMSO) were 575 ppb and 19.9 ppm, respectively, indicating the high susceptibility of P. caudatum to bromophos. The results indicate that the Paramecium toxicity assay could be used as a complementary system to rapidly elucidate the cytotoxic potential of compounds.

1. Acetylcholinesterase from the heads of a strain of houseflies selected for resistance to the carbamate insecticide methomyl, and from a methomyl-resistant field strain was found to be less sensitive to inhibition by methomyl than that from a susceptible strain. 2. The enzyme from resistant insects was also more tolerant to malaoxon, dichlorvos and bomyl but not to azamethiphos. 3. The decrease in sensitivity to inhibition appeared to be due to an increase in affinity for substrate.

1. Rats were used for studies on organophosphate (OP) toxicity both in acute and chronic cold exposure. Furthermore the effects of OPs on tissue acetyl- and butyrylcholinesterase activities were studied in the cold environment. 2. No change in the toxicity of dichlorovinyl phosphate (DDVP) was observed whereas that of diisopropylphosphofluoridate (DFP) increased 1.5-fold at +5 degrees C. 3. Chronic exposure to cold produced no change in DFP toxicity. 4. The survival time in acute cold exposure (1.1 x LD50 DFP) was longer than in chronic exposure or at +20 degrees C. 5. In control rats, chronic cold exposure increased blood BCHE and decreased BCHE in lungs. 6. A dose-dependent inhibition of cholinesterases was observed. 7. AcChE in the liver of chronically cold exposed rats was more sensitive to DFP inhibition compared to acute exposure. 8. Blood AcChE activity correlated only to AcChE in brain and lungs in rats.

Out of three most important classes of synthetic insecticides only the carbamates and pyrethroids were known to have ancestors in nature. Now two organophosphates (which are quite good insecticides and very potent acetylcholinesterase inhibitors, e.g. comparable to carbofuran) have been isolated from Streptomyces antibiotices antibioticus strain DSM 1951.

The cholinergic system of the brain was investigated in rats acutely poisoned with the organophosphate, 0,0-dimethyl 0-(2,2-dichlorovinyl) phosphate (DDVP), (6 mg/kg, sc, with saline as a control). The amounts of three fractions of acetylcholine (ACh)--free (extraterminal), labile-bound (intraterminal/cytoplasmic), and stable-bound (intraterminal/vesicular)--increased in the rats over a period of 5 to 60 min after injection of DDVP, showing peaks which were 2.45, 1.82, and 1.4 times as high as the respective control amounts. No difference was seen in the amount of any fraction of ACh between treated and control rats killed 3 and 24 hr after injection. Acetylcholinesterase (AChE) activity decreased to between 12 and 43% of the control over a period of 5 to 180 min and recovered almost completely within 24 hr after injection. No appreciable changes were seen in either spontaneous or potassium-induced ACh release in brain tissue slices obtained from rats treated with DDVP. ACh synthesis in slices was suppressed significantly 20 min, but not 24 hr, after injection of DDVP. In the brain crude synaptosomal preparation, high-affinity choline uptake, which is generally thought to be a rate-limiting step for ACh synthesis, was suppressed 20 min after DDVP. No appreciable changes were seen in high-affinity choline uptake at 24 hr low-affinity choline uptake, and choline acetyltransferase activity after injection of DDVP. These results suggest that ACh synthesis and high-affinity choline uptake may be in a suppressed state when ACh concentration, especially intraterminal ACh, is increased and AChE activity is decreased in the brain cholinergic system of rats poisoned with DDVP. The increase in the intraterminal ACh may be due to an inhibition of AChE activity at this site and/or a re-uptake of ACh in the synaptic cleft, not to an inhibition of ACh release or an increase in ACh synthesis.

Details of cases involving the inadvertent exposure of birds to eight toxic substances are recorded. The organophosphate insecticides dichlorvos, diazinon and malathion produced respiratory symptoms which in the former and latter cases were initially thought to be caused by infectious disease. Birds which consumed feed containing fenitrothion showed nervous signs before death. On three separate occasions feral starlings (Sternus vulgaris) were found dead and their gizzard contents contained mevinphos. The rodenticide warfarin was associated with petechial haemorrhages in the skeletal muscles and on the serosal surfaces of one hen. Cyanogenic glycosides from Eucalyptus cladocalyx were responsible for the sudden deaths of ducks and guinea fowl. 'Ornamental dough' containing sodium chloride was fed to birds which were deprived of water and they showed diarrhoea and nervous disorders before death.

DDVP (dichlorvos), an irreversible cholinesterase (ChE) inhibitor, was administered acutely and chronically to rats in order to investigate effects on the distribution of brain acetylcholine (ACh). In acutely treated animals (4 mg/kg, singly), cholinergic signs were evident and accompanied with a 100, 146, 113, and 61 per cent increase in total, free, labile-bound and stable-bound ACh content of the brain, respectively, and a 66 per cent decrease in acetylcholinesterase (AChE) activity 20 min after injection. In no animals treated chronically with a low dose (0.2 mg/kg/day for 9 or 90 days, or 1 mg/kg/day for 9 or 30 days), any overt sign was shown during the experimental period, and the stable-bound ACh content of the brain was not altered. In the group given 0.2 mg/kg for 90 days and that given 1.0 mg/kg for 9 or 30 days, free ACh content increased slightly but significantly, and AChE activity decreased to 58 per cent. Total ACh content and labile-bound ACh content increased only in a group given 1 mg/kg of DDVP for 30 days. These results suggest that acute, as well as chronic, exposure to organophosphate may induce alteration in mobilization and storage of ACh in the central cholinergic nerves.

The enzyme butyrylcholinesterase from horse serum catalyses the hydrolysis of certain esters. The orange-red 2,6-dichloroindophenyl acetate will be converted by the enzyme into a deep blue alcohol. The colour transformation does not occur when the enzyme is inactivated. By making use of this biochemical reaction a cheap and simple, but very sensitive and specific detection tube could bedeveloped. The tube comprises a breakable ampoule with an aqueous buffer solution, a freeze-dried preparation of the chromogenic ester with a filler promoting its dissolution, a freeze-dried preparation of butyrylcholinesterase with a filler promoting its stability, and an indication layer. DDVP can be detected at concentrations as low as 0.4 mg/m3, when the sampled airvolume is 21.

The following pesticides: azinphosmethyl, diallate, dichlorvos, EPTC, fenchlorphos, mevinphos, monocrotophos, noruron, parathionmethyl, triallate, trichlorphon and vegadex were tested for the ability to induce his+ revertants in four histidines requiring strains of Salmonella typhimurium--TAI 535(missense), TAI 536, TAI 537 and TAI 538 (frame-shift)- and resistance to low levels of streptomycin in Streptomyces coelicolor. Dichlorvos, which is a phosphoric ester with a dichlorovinyl group as side chain, and trichlorphon, which is known for its spontaneous conversion in dichlorvos, are both mutagenic in Salmonella (strain TAI535) and Streptomyces. Five organophosphorus pesticides similar to dichlorvos but devoid of the vinyl group are not mutagenic. Three carbamates, diallate, triallate and vegadex, which contain a chloroallyl group similar to the vinyl group of dichlorvos are mutagenic in Streptomyes; triallate and vegadex are powerful mutagens also in Salmonella (strain TAI535); two other carbamates devoid of the chlorinated group are not mutagenic. The results suggest that the presence of a vinyl chloride or allyl chloride group in the molecule of these pesticides is responsible for the ability to induce point mutations in Salmonella and Streptomyces.