The hematological effects of methyl parathion in rats

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Abstract

The effects of methyl parathion (MP) at sublethal concentration on hematological constituent [red blood corpuscles (RBC), white blood corpuscles (WBC), mean cell volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), platelet (PLT) counts, hemoglobin (Hb) and hematocrite (HCT) levels] and serum damage marker enzymes [aspartate aminotransferase (AST), alanin aminotransferase (ALT), alkaline phosphatase (ALP) and lactate dehydrogenase (LDH)] of rats were investigated under laboratory conditions. 5 and 10 ppm dosages of MP were administered orally to six female rats ad libitum during the tests for 4 weeks consecutively. MP treatments caused different effects on the hematological constituents and the serum marker enzymes of the treatment groups as compared to the controls. According to the results, MP treatments increased significantly the levels of serum marker enzyme activities except for ALT with both dosages and LDH with 5 ppm dosage. Also, the hematological constituents were affected by MP. For example, WBC significantly increased in rats treated with both dosages of MP whereas the other hematologic constituents did not change at 5 and 10 ppm of MP treatments. The observations presented led us to conclude that the administration of subacute MP elevates tissue damage serum marker enzymes, and increases the number of WBC in rats. These data, along with the determined changes suggest that MP produce substantial systemic organ toxicity in rats during the period of a 28-day subacute exposure.

Introduction

Environmental pollution by pesticide residues is a major environmental concern due to their extensive use in agriculture and in public health programs [1]. The environmental impact of pesticide use is related to several fundamental properties essential to their effectiveness as pesticides. First, pesticides are toxicants, capable of affecting all taxonomic groups of biota, including non-target organism, which to varying degrees depend on physiological and ecological factors. Secondly, many pesticides need to be resistant to environmental degradation so that they persist in treated areas and thus their effectiveness is enhanced. This property also promotes long-term effects in natural ecosystem [2]. Since pesticides are offered for plant protection, there has been improvement in the control of pest population and spread of infection born disease vectors. Public health programs in many developing countries including Turkey also utilize these studies as pesticides of choice to control disease-transmitting organism [3].

Methyl parathion (MP) is one of the most widely used organophosphate insecticides in agriculture. Organophosphorus insecticides (OPIs) are some of the most useful and diverse classes of insecticides in use for almost five decades. However, the uncontrolled use of these insecticides in agriculture and public health operation has increased the scope of ecological imbalance and thus many non-target organisms have become victims [4]. In literature, it is reported that OPIs are neurotoxic in nature by acting as inhibitors of neuronal cholinesterase (ChE) activity [5] and serum cholinesterase (SChE) [6]. Some studies have reported that OPIs cause lipid peroxidation [7], [8], [9] in vertebrates. Mutagenic effects of MP have been studied to determine the chemical's ability to cause a change in the DNA sequence of a gene. It was determined that MP, when administered to Wistar rats for a 6-week period of five treatment days per week at doses of 1/100, 1/75 and 1/50 of the LD50, displayed no significance effect in mutagenicity [10]. The cytogenetic and cytotoxic effects of OPIs and organochlorine compounds following a single dose administration were studied. It was found that the frequency of chromosomal aberrations and micronuclei in bone marrow cells and an assay of the liver expressed the genotoxic capabilities of these chemicals [11]. MP was reported to cause DNA damage in rats [12]. Further, it was found that MP, as a result a single-exposure, was the most hazardous tested organophosphate showing definite pathology in the livers of treated rats. It was also concluded from genotoxicity studies of organophosphorus pesticides that methyl parathion had some genotoxic effects [13]. MP did not show acute testicular toxicity; instead it caused subacute and subchronic testicular toxicity [14]. A significant increase in the percentage of abnormal sperm was observed in mice treated orally with MP [15]. MP caused a significant decrease in sperm count of rats [16].

MP is one of the most widely used OPIs in agriculture and public health programmes. MP is also one of the most used OPIs in the region of Van, Turkey. The aim of this study was to investigate the effects of subacute exposure of MP at sublethal dosages on serum marker enzyme activities and the change of hematological constituents after methyl parathion administration to mature female rats. To this end, the treatment of MP was done orally because of the effect of chemicals, which represent a well characterized in vivo toxicity model system.

Section snippets

Materials

The commercial parathion (O,O-diethyl-p-nitrophenyl-phosphorothioate), Bayer, 500 g/L) was used in experimentation. This stock solution was appropriately diluted with the test water to achieve the desired concentrations of MP.

Animals

Rats (Sprague–Dawley albino) weighing 150–200 g were provided by the animal house of the Sciences Faculty of Yuzuncu Yil University, and were housed in three groups, each group containing six rats. All animals were fed a group wheat–soybean–meal-based diet and water ad

Results

Following the exposure to 5 and 10 ppm dosages of MP, the body weight of rats were found to have been slightly reduced. The effects of MP administration on tissue damages index were evaluated as marker enzymes in serum samples from control and treated rats. The results showed that MP caused an increase in AST and ALP activities exposed with both dosages and also LDH with 10 ppm exposure (Table 1). With regard to the haematotoxicity of MP subacute exposure, no alteration in the hematological

Discussion

The effects of pollutants on nature became a field of interest for scientists from the beginning of the second half of 20th century, and subsequently investigation on the effect of these pollutants on human beings, plants and animals were initiated. MP is widely used throughout the world as a wide-spectrum insecticide for numerous harmful agricultural crops. Also, it has widely and effectively been used throughout the world with applications in agriculture and horticulture for controlling

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