Reduction In Cholinesterase Activity Research Articles

Biological monitoring of workers occupationally exposed to organophosphorus pesticides

AbstractThis paper describes the development and use of a biological monitoring method for assessing exposure to organophosphorus pesticides. The method is used to determine the concentration of six dialkyl phosphates and phosphoro‐thioates (dimethyl phosphate, diethyl phosphate, O,O‐dimethyl phosphorothioate, O,O‐diethyl phosphorothioate, O,O‐dimethyl phosphorodithioate and O,O‐diethyl phosphorodithioate) in urine. The method involves the azeotropic distillation of urine, derivatisation of the residue with pentafluorobenzylbromide followed by high resolution gas chromatography with flame photometric detection.The technique has been applied to the analysis of over 400 urine samples obtained from 140 workers with potential occupational exposure to organophosphorus pesticides during various agricultural activities, sheep dipping or pesticide formulation. Wherever possible, blood samples were taken for measurement of red blood cell and plasma cholinesterase activity. The results show that in over 300 instances where blood samples were also obtained, urinary dialkyl phosphate metabolites could be detected even though there was no depression of red cell or plasma cholinesterase activity. Formulation workers had higher urinary metabolite levels (expressed as nmoles metabolite per mmole creatinine) than any of the other groups studied and were the only group where a significant reduction in cholinesterase activity was also seen.The results discussed here show that the method for the analysis of urinary dialkyl phosphate metabolites described is useful for monitoring occupational exposure to organophosphorus pesticides and is capable of detecting low levels of exposure not detectable by depression of cholinesterase activity.

The effects of anticholinesterases on the latencies of action potentials in mouse skeletal muscles

1. The purpose of this investigation was to determine the long-term effects of a single dose of persistent anticholinesterases on muscle action potentials evoked by nerve stimulation. 2. Action potentials (APs), elicited by stimulation of the phrenic nerve, were recorded intracellularly in muscle fibres of mouse diaphragm. The time between stimulus and AP was measured and the variability of this latency was calculated during trains of APs. At the beginning of trains of APs there was an increase in latency, and this delay was also measured. 3. Within 3 h of subcutaneous injection, a single dose (500 nmol kg-1) of the anticholinesterase, ecothiopate produced about 90% reduction in the acetylcholinesterase activity of homogenates of mouse diaphragm muscle, but five days after injection, this activity was not different from values in untreated animals. The initial delay of APs and the variability of latencies were increased four fold and two fold respectively, remained at these maxima from the 1st to the 5th day after ecothiopate, and returned to the values in untreated animals between 15 and 27 days after ecothiopate. 4. These effects of ecothiopate on AP latency were dose-dependent and were also seen in extensor digitorum longus and soleus muscles. 5. Other anticholinesterases used were BOS (pinacolyl S-(2-trimethylaminoethyl)methylphosphonothioate), a quaternary compound, and diisopropyl fluorophosphate, a tertiary compound, which had effects similar to those of ecothiopate; the greater duration of the effects of this compound may be related to the greater duration of reduction in cholinesterase activity. 6. Ecothiopate had no effect on the delay or variability of latencies of endplate potentials which were recorded in cut-fibre preparations 5 days later. 7. It is concluded that the effects of ecothiopate on the latencies of indirectly-evoked muscle APs are postjunctional, may not be related to the degree of reduction in cholinesterase activity at the time of recording, and are not directly linked to necrosis.

Cholinergic deficit in Alzheimer's disease: a study based on CSF and autopsy data.

Cholinesterase (ChE) activity was measured as a possible marker of cholinergic neurotransmission of the brain in CSF of 93 patients with probable Alzheimer's disease/senile dementia of the Alzheimer type (AD/SDAT) and of 29 control patients. ChE activity in CSF was decreased significantly in the AD/SDAT patients as compared to the controls. This reduction correlated significantly with the various measures of the severity of dementia. However, the reduction of ChE activity was only moderate (25-30%) even in patients with the most severe dementia and nonsignificant in patients with early symptoms of AD/SDAT. The significance of various confounding factors, which may interfere with CSF ChE measurements is discussed. Our findings seem to indicate that the deficiency of cholinergic neurons is not directly reflected in CSF and that the measurements of ChE activities in CSF are not helpful in diagnosing AD/SDAT. In the autopsy study the activities of cholineacetyltransferase (ChAT) and ChE were determined for ten brain areas of 20 AD/SDAT patients and of 14 controls. In AD/SDAT patients ChAT activity was profoundly decreased (50-85% decrease) in the cortical areas and hippocampus, but was unchanged or only mildly reduced in other subcortical brain areas. This study further confirms that the affection of cholinergic neurons is limited to projections from nucleus basalis to cortex and hippocampus, whereas other cholinergic neurons, like in striatum, seem to be relatively spared. In general, the activities of ChAT and ChE were lower in Alzheimer patients dying at younger age suggesting more severe disease process with these patients.

Population and cholinesterase responses in fish exposed to malathion sprays

A population of young walleye in a shallow pond in Winnipeg was exposed to malathion after two aerial applications of this pesticide for mosquito control. The population was sampled frequently throughout the season for survival and growth estimates, and also for brain cholinesterase measurements since that enzyme was known to respond to malathion poisoning. Cholinesterase activity fell to about 25% of prespray values within 12 hr after the first spray, and then gradually recovered to about 80% of prespray values over 2 weeks. The same pattern was evident after the second spray, but the inhibition of cholinesterase activity was not quite as large. Fish captured for analysis showed no indication of the symptoms of organophosphorus insecticide poisoning. There have been a number of reports published linking cholinesterase inhibition with lethal and sublethal responses in exposed groups, but we are unaware of previous cases in which strong cholinesterase inhibition has been observed in a field population for which growth and survival statistics were available. This case, then, offered an opportunity to evaluate the biochemical response in terms of population parameters. The population statistics indicated small temporary decreases in both catch per unit effort and weight gains after the first spray. Evidently a reduction in cholinesterase activity to about 25% of preexposure levels was the approximate threshold for population effects.

Safety effectiveness of pesticide mixing-loading and application equipment used in 1976.

The effectiveness of currently used pesticide mixing-loading and application equipment in preventing workers from being exposed to cholinesterase (ChE) inhibiting pesticides was measured. Blood samples from workers involved in the application of pesticides in Monterey and Imperial counties of California were analyzed for ChE activity. The analyses indicated that only the mean red cell activity of mixer-loaders was significantly less than controls. Seasonal variations in ChE activity were noted for workers in Imperial County between January and August. These variations were apparently related to the toxicity of the pesticides used. A prototype, closed-transfer system used in Imperial County did not substantially reduce pesticide residues in the air around mixing-loading sites or prevent a reduction in ChE activity over that of open-transfer systems. This was attributed to inadequate training in the use of the new equipment on the part of the mixer-loaders and improperly maintained equipment. A protytype closed-transfer system used in Monterey County appeared to give some protection to mixer-loader applicators during the application season; however, the blood ChE activities of two mixer-loaders using another prototype closed system in Monterey County were severely depressed.

EFFICIENCY AND SAFETY OF METHIDATHION APPLIED AS A POUR‐ON SYSTEMIC INSECTICIDE FOR CONTROL OF CATTLE LICE

Methidathion applied to cattle as a pour-on insecticide for control of lice (predominantly Linognathus vituli, but also Haematopinus eurysternus and Damalinia bovis) caused a reduction in the lice population of approximately 98% to 99% in laboratory trials at the minimum recommended dose of 4 mg/kg and a 98.8% to 100% efficiency was achieved in field trials. In a comparative efficiency trial in the laboratory methidathion at 3.5 to 5 mg/kg reduced the lice population by 98.8% to 99%, fenthion by 98.5% at 4.5 mg/kg and famphur by 99.7% at 16.5 mg/kg. Methidathion was tolerated by calves aged 15 to 20 weeks at dose rates up to 40 mg/kg indicating an approximate 7 fold safety margin, but 1 of 4 calves treated at 50 mg/kg died following treatment. Treatment with fenthion at 50 mg/kg, 7.4 times the average recommended rate, famphur at 75 mg/kg, 3 times the average rate and chlorpyrifos at 85 mg/kg, 5 times average rate, caused reductions in whole blood cholinesterase activity of 52%, 27% and 47% respectively which were similar to the reductions in cholinesterase activity found in calves treated with methidathion at similar levels above the recommended commercial dose rates. It was found that 2 day old calves were more sensitive to treatment with methidathion than calves 9 or 16 days old. A further 11,900 cattle of varying age, breed and sex were treated with methidathion under field conditions at the recommended rate of 4 to 8 mg/kg, and 534 cattle were treated at 24 mg/kg without any signs of toxicity.

Reduction in the cholinesterase activity of the rat anococcygeus muscle produced by corticosterone.

1 Administration of corticosterone caused a 47% reduction in the cholinesterase (ChE) activity of homogenates of the rat anococcygeus muscle. 2 ChE activity was also reduced by morphine withdrawal and this effect was abolished by the corticosteroid synthesis inhibitor, metyrapone. 3 A single dose of reserpine reduced ChE activity in normal but not in adrenalectomized rats. 4 ChE activity was increased by adrenalectomy or by metyrapone treatment. 5 The mechanism of the corticosteroid-induced reduction in ChE activity is discussed. 6 The reduction in ChE activity produced by corticosterone, morphine withdrawal, or a single dose of reserpine might explain the leftward shift of the dose-% response curve to acetylcholine produced by these procedures in the isolated anococcygeus muscle of the rat.

Effects of Nicotine and Acetylcholine On Denervated Chick Biventer Cervicis Muscles

Chick biventer cervicis muscle was chronically denervated for various periods of time. The muscle lost its responses to indirect electrical stimulation on the nerve as expected. It remained responsive to ACh although the contraction force was somewhat reduced, depending on the length of time after denervation. The denervated muscle was approximately 10-fold more sensitive to ACh than the innervated one was. This is presumably due to the reduction of cholinesterase activity in the denervated muscle. The responses of nicotine were reduced much more than those of ACh in denervated muscles. The result supports the hypothesis that ACh is released by nicotine to produce nicotine responses. The residual responses produced by nicotine in denervated muscle could be due to the release of ACh from the fine diffuse nerve fibres which can not be denervated completely with surgical procedures, and to the reduction of cholinesterase activity which potentiates the responses of minute quantities of ACh released by nicotine.

Analysis of local cholinergic tremor mechanisms following selective neurochemical lesions

Specific neurochemical lesions produced by intracaudate injections of anticholinesterases produced resting tremors in unanesthetized cats. The tremors reflect an intense and persistent activation of muscarinic acetylcholine (ACh) receptors by abnormally elevated levels of endogenously released ACh which accumulated during the reduction in cholinesterase activity. The progression of anticholinesterase (endogenous) tremors was divided into three-stages: maximal, postmaximal, and residual. The first two stages (acute) were suppressed by locally injected agents which reduced ACh function: HC-3 (interference with ACh synthesis); scopolamine (antagonism at ACh receptors); and large doses of pentobarbital (reduced ACh release), as well as by locally injected catecholamines, dopamine and epinephrine (inhibition at beta-catecholamine receptors). Evidence suggests that elevated ACh levels promote the release of dopamine, thereby comprising an early but limited compensatory system. Residual tremors involve neurotoxic processes in addition to cholinesterase inhibition that increase the sensitivity of receptors to acetylcholine and account for the persistence of residual tremors and their differential resistance to drug inhibition. Our studies substantiate the hypothesis that acetylcholine and dopamine in the caudate nucleus constitute an important tremor-regulatory system.