| Dimethoatc (O,O-dimcthyl 5-mcthyl carbamoylmethyl phosphorodithioate, DM) is one of organophosphorus insecticides with anticholinesterase activity, used in agriculture to treat fruit trees, olive trees, vegetable plants, ornamental plants, tobacco, cotton, and other crops. It is the most widely used as a pesticide in China. DM is often a cause of accidental or suicidal poisoning. Deliberate self-harm by ingestion of organophosphorus insecticides is a common health problem all over the world, most in the developing country. Once it has entered the body, it undergoes metabolic activation by oxidative desulfuration to omethoate .The poisoning results in an initial life-threatening cholinergic crisis and several intermediate and late neurological and psychiatric manifestations.Symptoms of acute exposure to organophosphale or cholinesterase-inhibiting compounds may include the following: numbness, tingling sensations, incoordination, headache, dizziness, tremor, nausea, abdominal cramps, sweating, blurred vision, difficulty breathing or respiratory depression, and slow heartbeat. Very high doses may result in unconsciousness, incontinence, and convulsions or fatality. Persons with respiratory ailments, recent exposure to cholincsterase inhibitors, impaired cholinesterase production, or liver malfunction may be at increased risk from exposure to DM. Mutagenic effects due to dimcthoate exposure were seen in mice. An increase in malignant tumors was reported in rats given oral doses of 5. 15 or 30 mg/kg/day dimcthoate for over a year. The toxicity of the DM was extensively studied. However, many problems, e.g., the effect of DM on the monoamines ncurotransmittcrs in the rat brain and the mechanisms, are still unsolved and became the object of this study. This report summarizes our recent findings regarding the changes of neurotransmittcr and their biosynthesis metabolic enzyme that occur in discrete brain regions and serum. The results are discussed in relation to the mechanisms controlling the nerve agent DM-induccd seizures and ncuropathology.A rapid, reliable and simple method detecting monoamine ncurotransmitters in rat serum and brain tissue by high performance liquid chromatography with electrochemical detector was developed. An ODS column was selected as separation column at room temperature, and the mobile phase (pH4.50) consisted of .0.02M trisodium citrate and 0.05M disodium phosphate.containing 15 %mcthanol(volumc ratio)in distilled water. The mobile phase was pumped at a flow rale of 1.0ml/min and the oxidation potential was set at +0.65V. Dihydroxybenzylaminc was used as the internal standtard for quantification. Four compounds. epinephrine(E),dopamine(DA) and 5-hydroxytryptaminc(5-I(?)T) in the brain tissue(wholc cerebral cortex, hippocampus, slriatum. midbrain. cerebellum) and serum were simultaneouslyseparated and determined under the above conditions. RSD% of the retention times and peak areas of standard sample was in the range 0.29-0.67 and 0.09-0.36.The recoveries of all analytes were over 85%.The detection limits of 0.083ng/ml for NE,0.51ng/ml for E,0.046 ng/ml for DA and 0.078 ng/ml for 5-HT were achieved with standard solutions. The linearity is over the range 1.0-100 ng/ml for NE, 5.0-80 ng/ml for E, 1.0-80 ng/ml for DA and 1.0-60 ng/ml for 5-HT. The assay has been applied successfully to measure simultaneously cortex and serum concentrations of these four monoamincs in rats.The alterations of monoaminc levels in the rat brain and serum were determined after the Dimelhoale(DM) induced intoxication, including the alterations of (?)pincphinc(NE), cpinephinc(E). serotonin(5-HT), dopamine(DA) and its metabolite (3.4-hydroxypheny(?)aceticacid, DOPAC) level. Groups of rats were treated with saline and 38.9. 83.7 and 180 mg/kg DM respectively and were decapitated at different lime course from 0.5 to 24 hours after the administration. The monoamines ncurotransmitters were determined by reverse-phase high-performance liquid chroniatography with electrochemical detection. The concentrations of DA(8-296% of control). DOPAC(13-67% of control) and 5-HT(3-27% of control) increased according with the DM dose and the exposure time, while the levels of NE(10-55 % of control) and E.(11-33% of control) contents decreased at the same time. These findings indicate that DM-induced toxic effects can alter the monoamine levels after the different dose and time exposure in the rat brain and scrum suggesting that monoaminergic mechanism is involved in the DM intoxication.To testify monoaminergic mechanism, the change of enzyme dopamine β-hydroxylase (Dβ(?)) activity in the rat striatum and scrum was determined after the dimethoate (DM) induced intoxication. The 3 administration groups received DM (38.90mg/kg, 83.70mg/kg. 180.0mg/kg, respectively) and killed at different time-course(0.5,2.8,24h respectively )after DM administration. The DβH activity is determined by reverse-phase high-performance liquid chromatography with electrochemical detection. Levels of DβH activity (6-59% of control) decreased with the increase of DM dose and changed with different time-course. Level change of DβH activity in dose-effect showed significant linear relationship (correlation r= -0.9967) at 2h time-course in the rat striatum and serum. These findings indicated that DM-induced toxic effects can decline DβH activity level in different exposure dose and at different treated time-course, suggesting that different toxic effect mechanisms arc involvedThe activity of monoaminc oxidase (MAO) in the rat striatum and scrum was also determined after the dimethoate (DM) induced intoxication. No significant changes of MAO activity level were observed with,the increase of DM dose and changed with different lime-course. These results indicated that DM-induced toxic effects can not change MAO activity level in different exposure dose and at different treated time-course, suggesting that toxic effect mechanisms dimethoate induced intoxication arc not involved in the inhibition of MAO.These changes in monoaminergic systems include a significant increase in the turnover rate of DA and marked release and depletion of NE. and E ensued, the inhibition of enzyme dopamine β-hydroxylase (DβH) activity or the reduction in DβH, not the inhibition of monoamine oxidasc (MAO). Some tests are designed to determine the activity of DβH. The findings testify that a slow inhibition of DβH activity or the reduction in DβH content result in concurrent elevation of DA and decrease in levels of NE and E.A rapid, reliable and simple method detecting dopamine (DA) and two metabolites of DA. 3. 4-hydroxyphcnylaccticacid(DOPAC) and homovanillic acid (HVA) in the rat nigrostriatal slice by high performance liquid chromatography with electrochemical detector was also developed. An ODS column was selected as separation column at room temperature, and the mobile phase (pH4.50)consisted of 0.02M trisodium citrate and 0.05M disodium phosphatc.containing 10 % acetonitril(volumc ratio)in distilled water. The mobile phase was pumped at a flow rate of 1.0ml/min and the oxidation potential was set at +0.85V. RSD% of the retention times and peak areas of standard samples was in the range 0.34-0.47, 0.61-0.78 and 0.41-0.58. The recoveries of all analytes were over 85%.The detection limits of 0.045ng/ml for DA.0.18ng/ml for DOPAC.0.36 ng/ml for HVA were achieved with standard solutions. The linearity is over the range 1.0-100 ng/ml for DA. 5.0-100 ng/ml for DOPAC and 5.0 100 ng/ml forHVA .The assay has been applied successfully to measure simultaneously concentrations of these dopamine (DA) and two metabolites of DA. DOPAC and HVA in the rat nigrostriatal sliceThe alterations of dopamine (DA) and two metabolites of DA. DOPAC and HVA in the rat nigrostriatal slice were determined after the dimcthoate (DM) induced intoxication. Groups of slices were treated with saline and 3.89. 8.37 and 18 mg/ml DM respectively at 2hr time cousc, and were treated with 18 mg/ml at different time course from 0.5 to 24 hours. The levels of DA, DOPAC and HVA were determined by reverse-phase high-performance liquid chromatography with electrochemical detection. The concentrations of DA (36-260% of control). DOPAC (9-302% of control) and HVA (18-696% of control) increased according with the DM dose and the exposure time. These findings further demonstrate that DM-induced toxic effects can alter the levels of DA. DOPAC and HVA after the different dose and time exposure in the rat nigrostriatal slice, suggesting that monoaminergic mechanism is involved in the DM intoxication.In conclusion, the dimcthoate is not only a cholinesterase-inhibiting compound but also a dopamine-β-hydroxylase inhibitor. These findings prove the monoaminergic mechanism in the DM intoxication.
|
PDF Full Text Request