Influence of methyl parathion on reproductive parameters in male rats

Exposure of human population to pesticides and industrial pollutants has considerably increased the risk of human health hazard. In the present study, therefore we have sought to investigate the toxic effects of Methyl Parathion on male reproductive system of rat. The tested dose was given orally to the rats for 30 days at the dose level of 30 mg/kg/day. Sex organs weight analysis, histochemical and histopathological changes and mating trials were the criteria used to evaluate the reproductive efficacy of the treated rats. The body weight of the animals did not show any significant change. However, Methyl Parathion caused significant decrease in the weight of testis, epididymis, seminal vesicle and ventral prostate with marked pathomorphological changes. Also, marked reduction in epididymial and testicular sperm counts in exposed males were noticed. Fertility test showed 80% −ve fertility in treated animals. A significant reduction in the sialic acid contents of testis, epididymis, seminal vesicle, ventral prostate and testicular glycogen were noticed, while the protein and cholesterol content were raised significantly. From the above-mentioned findings, it has been concluded that exposure to Methyl Parathion has deleterious effects on male reproductive system of rat. Therefore, application of such insecticide should be limited to a designed program.     

Comparative toxicity, anticholinesterase action and metabolism of methyl parathion and parathion in sunfish and mice

The in vitro metabolism of methyl parathion (O,O-dimethyl O-p-nitrophenyl phosphorothioate) and parathion (O,O-diethyl O,p-nitrophenyl phosphorothioate) and the sensitivities of the target cholinesterases to inhibition by their oxygen analogs were studied in sunfish (Lepomis gibbosus) and mice to determine the basis for the low toxicity of methyl parathion in sunfish (LD50 > 2500 mg/kg). The LD50 values of parathion and methyl parathion in mice were 13.5 and 11 mg/kg, respectively, and the times to death were much shorter for both compounds in mice than in fish. Low sensitivity of fish cholinesterases to paraoxon as compared to mice accounted for the 10-fold lower toxicity of parathion in fish (LD50, 110 mg/kg). By contrast, sunfish had similar cholinesterase sensitivities to methyl paraoxon and paraoxon. Differences in rates of oxidative formation of the oxygen analog or oxidative cleavage to p-nitrophenol and the corresponding dialkyl thiophosphate could not account for the selective resistance of sunfish to methyl parathion toxicity. Fish and mouse liver homogenates catalyzed a glutathione (GSH)-dependent metabolism of methyl parathion and methyl paraoxon but not of parathion or paraoxon. Additionally, hydrolysis of methyl paraoxon by fish liver homogenates exceeded that for parathion by 5-fold, while methyl paraoxon hydrolysis in mice was $\text{1}\text{2}$ of that of paraoxon. Apparently, a longer time to death in fish provided the opportunity for GSH-dependent and hydrolytic detoxification, which favored methyl parathion and methyl paraoxon relative to parathion and paraoxon. Although in mice the GSH-dependent enzymes also favored detoxification of methyl parathion and methyl paraoxon, this is apparently of less importance because of their high cholinesterase sensitivity and because cleavage and hydrolysis favored parathion and paraoxon.     

Biotransformation of the organophosphorus insecticides parathion and methyl parathion in male and female rat livers perfused in situ.

Although numerous previous reports have characterized the mammalian biotransformation of the organophosphorus insecticides parathion and methyl parathion, questions still remain regarding the toxicological significance of certain metabolic pathways in vivo. The present study utilized rat liver perfusions in order to better characterize the hepatic biotransformation of parathion and methyl parathion in intact liver. Single-pass liver perfusions with parathion and methyl parathion over a range of perfusate concentrations of 10-80 microM resulted in the appearance of paraoxon and methyl paraoxon, respectively, in effluent. Furthermore, rat blood did not have the capacity to prevent transport of paraoxon and methyl paraoxon to extrahepatic tissues, suggesting that oxon produced hepatically can distribute to extrahepatic tissues. In addition, striking sex differences were noted in the metabolite profile of parathion and methyl parathion in perfused livers. However, these differences could not account for the observation that females are more susceptible to parathion, but less susceptible to methyl parathion, compared to males. And finally, S-methyl glutathione or S-p-nitrophenyl glutathione could not be detected in effluent or bile of livers from either sex perfused with methyl parathion, suggesting that glutathione-dependent detoxification of this insecticide does not occur to any significant degree in intact rat liver.     

Interactive toxicity of the organophosphorus insecticides chlorpyrifos and methyl parathion in adult rats

The acute interactive toxicity following exposure to two common organophosphorus (OP) insecticides, chlorpyrifos (CPF) and methyl parathion (MPS), was investigated in adult male rats. Oral LD1 values were estimated by dose-response studies (CPF = 80 mg/kg; MPS = 4 mg/kg, in peanut oil, 1 ml/kg). Rats were treated with both toxicants (0.5 or 1 x LD1) either concurrently or sequentially, with 4-h intervals between dosing. Functional signs of toxicity (1-96 h) and cumulative lethality (96 h) were recorded. Rats treated with CPF (1 x LD1) did not show any signs of toxicity although MPS (1 x LD1) elicited slight to moderate signs (involuntary movements) within 1-2 h. Concurrent exposure (LD1 dosages of both CPF and MPS) caused slight signs of toxicity only apparent between 24 and 48 h after dosing. When rats were treated sequentially with MPS first followed by CPF 4 h later, slight signs of toxicity were noted between 6 and 24 h, whereas reversing the sequence resulted in 100% lethality within 1 h of the second dosage. Following exposure to lower dosages (0.5 x LD1), the CPF first group showed higher signs of cholinergic toxicity compared with MPS first or concurrent groups. Cholinesterase inhibition in plasma, diaphragm, and frontal cortex was generally higher in rats treated sequentially with CPF first than in those treated initially with MPS from 4 to 24 h after dosing. Plasma and liver carboxylesterase inhibition at 4 h was also significantly higher in the CPF first (62-90%) compared with MPS first (22-43%) group, while at 8 and 24 h, there was no significant difference between any of the treatment groups. ChE inhibition assays to evaluate in vitro hepatic detoxification of oxons indicated that carboxylesterase (CE)- and A-esterase-mediated pathways are markedly less important for methyl paraoxon (MPO) than chlorpyrifos oxon (CPO) detoxification. CPF pretreatment blocked hepatic detoxification of methyl paraoxon while MPS pretreatment had minimal effect on hepatic CPO detoxification ex vivo. These findings suggest that the sequence of exposure to two insecticides that elicit toxicity through a common mechanism can markedly influence the cumulative action at the target site (acetylcholinesterase, AChE) and consequent functional toxicity.     

Renal damage induced by the pesticide methyl parathion in male Wistar rats

Little information is apparently available regarding the nephrotoxic effects induced by pesticides. The aim of this study was to examine the influence of low doses of methyl parathion (MP) on the structure and function of the kidney of male Wistar rats. A corn oil (vehicle) was administered to control rats, whereas treated rats received MP at 0.56 mg/kg orally (1/25 of LD₅₀), every third day, for 8 weeks. At the end of each week following MP exposure, creatinine and glucose levels were measured in plasma, while glucose, inorganic phosphate, total proteins, albumin, and activity of γ-glutamyltranspeptidase (GGT) were determined in urine. Kidney histological study was also performed. Compared with control rats, MP significantly increased plasma glucose and creatinine levels accompanied by decreased urinary flow rate and elevated urinary excretion rates of glucose, phosphate, and albumin. Further, the activity of GGT in urine was increased significantly. The proximal cells exhibited cytoplasmic vacuolization, positive periodic acid Schiff inclusions, and brush border edge loss after 2 or 4 weeks following MP treatment. Finally, renal cortex samples were obtained at 2, 4, 6, and 8 weeks of MP treatment, and the concentrations of reduced glutathione (GSH) and glutathione peroxidase (GPx) activity were measured. The mRNA expression levels of BAX and tumor necrosis factor-α (TNF-α) were also determined (RT-PCR). MP significantly decreased renal GSH levels, increased GPx activity, as well as downregulated the mRNA expression of TNF-α and BAX. Densitometry analysis showed a significant reduction in TNF-α and BAX mRNA expression levels at 2 and 4 weeks following MP treatment. Low doses of MP produced structural and functional damage to the proximal tubules of male rat kidney.     

The acute toxicity of four trihalomethanes in male and female rats

The acute toxicity of chloroform, bromodichloromethane, chlorodibromomethane, and bromoform was investigated in rats. The clinical signs observed following single oral doses of the test compounds were sedation, flaccid muscle tone, ataxia, piloerection, and prostration. Gross pathological examination revealed liver and kidney congestion. Median lethal doses (LD50) of the four trihalomethanes were calculated using the probit analysis. While male rats appeared to be more susceptible than the females to the lethal effect of chloroform (LD50 in mg/kg: male, 908; female, 1117) and bromodichloromethane (LD50: male, 916; female, 969), the females were found to be more sensitive than the males to chlorodibromomethane (LD50: male, 1186; female, 848) and bromoform (LD50: male, 1388; female, 1147).     

Subacute toxicity of trichloroacetic acid in male and female rats

Trichloroacetic acid, TCA, is a water chlorination by-product similar to dichloroacetic acid, DCA. Because DCA has been shown to have effects on intermediary metabolism, TCA was tested to determine if it possesses similar capabilities. The effects were more pronounced in females. High doses of TCA (2.45 mumol/kg three times) decreased plasma glucose and lactate concentrations and liver lactate concentration. DCA had similar, less pronounced effects. In males DCA and TCA each decreased plasma lactate concentrations. Rats were exposed to TCA in drinking water for 14 days. The highest concentration (2.38 g/l) caused decreases of water and food consumption and loss of body weight. At 7 days females had decreased urine volume accompanied by a modest increase of urine osmolality, resulting in a significant decrease of excretion of solute. Concentrations of glucose in plasma and lactate in tissues were not significantly affected by this subchronic TCA exposure. These results indicate that TCA may have effects on intermediary metabolism similar to those of DCA.     

Comparative metabolism of methyl isobutyl carbinol and methyl isobutyl ketone in male rats

Methyl isobutyl carbinol (MIBC) is an oxygenated solvent that is metabolized to methylisobutyl ketone (MIBK) and then to 4-hydroxymethyl-4-methyl-2-pentanone (HMP). Plasma levels of MIBC, MIBK and HMP were determined up to 12 h after a single oral 5 mmol/kg dose of MIBC or MIBK to male rats. The major material in the plasma in both cases was HMP, with similar areas-under-the-curve (AUC) and C(max) at 9 h after dosing. MIBK plasma levels and AUC were also comparable after MIBK or MIBC administration. MIBC AUC was only about 6% of the total material in the blood after MIBC, and insignificant after MIBK administration. No other metabolites were detected in the plasma under the analytical conditions used. The extent of metabolism of MIBC to MIBK, by comparing combined AUCs for MIBK and HMP, was at least 73%. The limited systemic toxicity data for MIBC are consistent with those for MIBK, which has been well studied. The metabolic equivalency of MIBC with MIBK indicates that MIBC will have a low potential for toxicity similar to that of MIBK, and reduces the need for additional animal studies.     

Prolonged toxicity with intermediate syndrome after combined parathion and methyl parathion poisoning.

A prolonged type of organophosphate toxicity, previously characterized as the Intermediate Syndrome, has been recognized in 6 out of 7 prospectively studied patients poisoned by insecticide containing parathion and methyl parathion in equal proportions. The clinical characteristics included respiratory paresis, weakness in the territories of several motor cranial nerves, neck flexors and proximal limb muscles, and depressed tendon reflexes, all lasting for several days or weeks. Electromyography in the early stages disclosed diverse types of impaired neuromuscular transmission. EMG normalization preceded clinical recovery. Severe plasma butyrylcholinesterase and erythrocyte acetylcholinesterase inhibition persisted along with the occurrence of Intermediate Syndrome-related symptoms. We conclude that combined parathion and methyl parathion poisoning is more likely to induce Intermediate Syndrome than parathion poisoning alone. The mechanisms underlying this difference remain obscure. The Intermediate Syndrome shows clinical and electromyographic hallmarks of combined postsynaptic impairment of neuromuscular transmission.     

Riboflavin and drug metabolism in adult male and female rats

Oxidative metabolism of drugs in vitro in liver 9000 g supernatant fraction from riboflavin-deficient adult male and female rats was investigated. A significant decrease in overall oxidation of aminopyrine, ethylmorphine, N-methylaniline, aniline and acetanilide was observed. Studies at two deficiency levels indicate that a marked decrease in specific activities of N-demethylation of aminopyrine. ethylmorphine. N-methylaniline and hydroxylation of aniline and acetanilide occurs in both male and female rats. The levels of drugmetabolizing enzymes were further lowered with increase in deficiency. The levels of flavin, NADPH cytochrome c reductase, cytochrome P-450 and cytochrome b₅ were reduced in riboflavin-deficient (7 weeks) male rats as compared to normal rats. The activity of drug enzymes from riboflavin-deficient rats was stimulated by pretreatment with phenobarbital. A significant reversal of drug enzyme activities was noted when riboflavin was administered to deficient animals.     

Human placental glutathione S-transferase-mediated metabolism of methyl parathion

The ability of human placental glutathione S-transferase (GSHTr) to metabolize methyl parathion (MeP) was examined. MeP was found to be a substrate for both partially purified pre-term and highly purified term placental GSHTr. The characterization of the reaction by high performance liquid chromatography revealed the presence of desmethyl parathion (DesMeP) as the sole metabolite. Term placental GSHTr activity towards MeP ranged from 2.22 to 3.53 nmoles DesMeP formed X min-1 X mg-1 while an activity of 0.60 to 1.12 nmoles DesMeP formed X min-1 X mg-1 was observed with the pre-term placental enzyme. The absence of the O-dearylation reaction by pre-term and term placental GSHTr represents a major species- and/or tissue-specific difference.     

Reproductive toxicity associated with acrylamide treatment in male and female rats

The present study was designed to evaluate the influence of acrylamide (ACR) on male and female reproductive function. Male rats received ACR in drinking water (50, 100, or 200 ppm) for up to 10 wk. Copulatory behavior, semen, and (for controls and 100 ppm only) fertility and fetal outcomes were evaluated. Females received ACR (25, 50, 100 ppm) for 2 wk prior to initiation of breeding and then throughout gestation and lactation. Hindlimb splaying was apparent in the 200-ppm males by wk 4; less severe splaying appeared in the 100-ppm group at wk 8. Disruptions in copulatory behavior preceded the appearance of this ataxia. These disruptions in mating performance interfered with ejaculatory processes and subsequent transport of sperm, since semen was found in the uterus of only 1 of the 15 females mated with the 100-ppm males at wk 9. Moreover, only 33% of the females mated (wk 10) to the 100-ppm males were pregnant. Postimplantation loss was also significantly increased in this group. Hindlimb splaying appeared in the females receiving 100 ppm ACR during wk 1-2 of pregnancy. Body weight and fluid intake were also depressed. Dams in the 50-ppm group showed depression in these parameters during the last 2 wk of lactation. ACR did not significantly affect mating performance of the females, pregnancy rates, litter size, or survival. However, ACR did significantly depress pup body weight at birth (100-ppm group) and weight gain during lactation through post-weaning, d 42 (50- and 100-ppm groups). Vaginal patency was delayed in the 100-ppm group only.     

Further observations on the difference in the metabolism of histamine in male and female rats

In young rats a sex difference in the daily output of free histamine in the urine did not become apparent until after the 26th day of life, when males exhibited a lower excretion. Castration increased the urinary free histamine in male rats but had little or no effect in females. Testosterone depressed the urinary free histamine in castrated male and female rats, but did not change the excretion in intact females. When [¹⁴C]-histamine was given by subcutaneous injection, the fraction of the dose appearing in the urine in the unchanged form followed closely the excretion of endogenous free histamine. Parallel changes were also seen in the amounts of [¹⁴C]-histamine excreted after injection of [¹⁴C]-(—)-histidine. Intact male rats methylated [¹⁴C]-histamine given by injection and [¹⁴C]-histamine formed in the body more efficiently than did castrated males and females. Testosterone increased the degree of methylation of injected [¹⁴C]-histamine and of [¹⁴C]-histamine formed in the body. It is suggested that androgenic hormones increase the rate of histamine methylation in the rat and that this effect provides a satisfactory explanation for the lower excretion of urinary histamine in male rats.     

Dose-dependent actions of thyroxine on hepatic drug metabolism in male and female rats

Studies were carried out to compare the effects of various doses of thyroxine (T₄) on hepatic drug metabolism in male and female rats and to evaluate the role of the pituitary gland in the modulation of T₄ action. Administration of small amounts of T₄ (2.5 to 5 μg/100g body wt/day) to hypophysectomized rats of either sex increased hepatic ethylmorphine demethylase, benzo(a)pyrene hydroxylase and aniline hydroxylase activities. Larger amounts of T₄ (12.5 to 50 μg) reversed the stimulatory effects of the smaller doses. T₄ treatment produced dose-dependent decreases in hepatic cytochrome P-450 content and increases in NADPH-cytochrome c reductase activity in hypophysectomized rats of both sexes. Qualitatively similar effects were produced by T₄ administration to thyroidectomized male and female rats. However, larger doses of T₄ were required for maximum stimulation of drug metabolism in thyroidectomized than in hypophysectomized animals. The results indicate that physiological amounts of T₄ Uniformly stimulate hepatic drug metabolism in both male and female rats. Supraphysiological amounts, however, inhibit metabolism of some substrates and produce sex differences in T₄ actions. The effects of T₄ are demonstrable in the absence of the pituitary gland but pituitary-dependent factors appear to modulate the magnitude of the response to T₄.     

Evaluating acute toxicity of methyl parathion application in constructed wetland mesocosms

Wetland ecosystems have reduced ambient levels of various organic and metallic compounds, although their effectiveness on agricultural pesticides is not well documented. Five stations within each of two 10 x 50 m constructed wetlands (two vegetated, two nonvegetated) were selected to measure the fate and effects of methyl parathion (MeP). Following a simulated storm event (0.64 cm of rainfall), aqueous, sediment, and plant samples were collected and analyzed spatially (5, 10, 20, and 40 m from the inlet) and temporally (after 3-10 days) for MeP concentrations and for the impact of those concentrations on the aquatic fauna. Aqueous toxicity to fish decreased spatially and temporally in the vegetated mesocosm. Pimephales promelas survival was significantly reduced, to 68%, at the 10-m station of the nonvegetated wetlands (3 h postapplication), with pesticide concentrations averaging 9.6 microg MeP/L. Ceriodaphnia in both the vegetated and nonvegetated wetlands was sensitive (i.e., a significant acute response to MeP occurred) to pesticide concentrations through 10 days postapplication. Mean MeP concentrations in water ranged from 0.5 to 15.4 microg/L and from 0.1 to 27.0 microg/L in the vegetated and nonvegetated wetlands, respectively. Hyalella azteca aqueous tests resulted in significant mortality in the 5-m vegetated segment 10 days after exposure to MeP (2.2 microg/L). Solid-phase (10-day) sediment toxicity tests showed no significant reduction in Chironomus tentans survival or growth, except for the sediments sampled 3 h postapplication in the nonvegetated wetland (65% survival). Thereafter, midge survival averaged >87% in sediments sampled from both wetlands. These data suggest that wetlands play a significant role in mitigating the effect of MeP exposure in sensitive aquatic biota.     

The effect of various centrally-acting drugs on hepatic steroid metabolism in male and female rats.

The effects of various centrally-acting drugs on steroid metabolism in the liver and pituitary hormone concentration in the serum of male and female rats were investigated using well characterized and tested methods. It was seen that picrotoxin, morphine and LSD had a general stimulatory action on hepatic steroid metabolism (morphine only in the female) whereas thiosemicarbazide was without effect. Clonidine gave a move towards a more “female” type of metabolism in the male animals. All drugs tested except thiosemicarbazide had effects on pituitary hormone secretion although not always the effects that have been previously reported. Discrepancies from previous reports are discussed. Correlations between changes in hepatic steroid metabolism and changes in pituitary hormone secretion can be observed but are not consistent. It is concluded that, of the drugs tested, only clonidine may have an effect on “feminizing factor” secretion indicating that this may be controlled in part by the noradrenergic system of the brain.