Protective effect of early and late administration of pralidoxime against organophosphate muscle necrosis.

The objective of the present investigation was to study the protection afforded by a single administration of pralidoxime against the muscle necrosis induced by the organophosphate compound metamidophos at different times after intoxication. The fiber necrosis of the diaphragm muscle was quantified by a morphometric technique, comparing the area fraction occupied by necrotic muscle fibers in animals that received pralidoxime at different times after intoxication, i.e., 0, 1, 3, 6, and 12 h. Pralidoxime administration protected metamidophos-induced muscle necrosis in all groups studied except for the 12-h group. The earlier the administration of pralidoxime the greater the protection against muscle necrosis. This protection was not accompanied by complete reactivation of plasma cholinesterase activity. Results support the current opinion that pralidoxime should be administered as soon as possible after organophosphate intoxication, because in addition to reversing the muscarinic effects, early administration of pralidoxime also prevents muscle necrosis--which could impair muscular function and respiratory condition. The time difference between recovery of plasma cholinesterase activity and muscle necrosis protection indicates that this method is not completely trustworthy for patient follow-up, since some improvement may occur in spite of the low plasma cholinesterase activity.

Histologic peripheral nerve changes in rats induced by deltamethrin.

Synthetic pyrethroid insecticides have been used in the last two decades largely because of their high activity as an insecticide and low mammalian toxicity. Some studies have demonstrated that these products, especially compounds with an alpha-cyano group, are toxic to the mammalian central nervous system (CNS) in acute intoxications. However, morphological studies are scarce. In the present work the histopathologic changes of the sciatic and tibial nerves of rats submitted to acute intoxication with the cyanopyrethroid deltamethrin were studied. For 3 consecutive days male Wistar rats received by oral gavage deltamethrin at a dose of 45 mg/kg body wt. On the 4th day fragments of sciatic and tibial nerves were studied by transmission electron microscopy (TEM) and teasing of individual nerve fibers. In addition, another group of rats were allowed to recover until the 10th day. Teasing of nerves of animals sacrificed on the 4th day revealed myelin ovoids, which are indicative of axonal damage. TEM demonstrated rare degenerated axons completely filled with organelles, in particular mitochondria, and with electron-dense lamellar bodies that resemble myelin figures. In addition, great cytoplasmic vacuolization caused by proliferation and dilation of the rough and smooth endoplasmic reticulum and Golgi apparatus was observed in some Schwann cells. No lesion was found 7 days after discontinuation of the treatment (group2). Since these histologic changes are transitory and scarce, the question arises: Are they related to the changes in NA(+), K(+)-ATPase activity or Na(+) channels caused by pyrethroid compounds?

Early expression of ubiquitin in myofibers of rats in organophosphate intoxication.

The degenerative process of the myofibers of the diaphragm of rats intoxicated with the organophosphate isofenphos, a compound that inhibits esterases, was studied at different intervals of intoxication. Early disorganization of the intermyofibrillar network and of the myofilaments, as well as dilatation of organelles, were observed by use of transmission electron microscopy. These changes precede macrophage invasion of the muscle fibers. Early expression of ubiquitin was observed in segments of muscle fibers by immunohistochemistry. Bands of polyubiquitin complexes in muscle homogenates were observed by immunoblotting. These bands disappeared in later stages of intoxication. A 42.5-kDa band corresponds to actin, as observed by immunoblotting using antisarcometric actin. This indicates relatively large amounts of polyubiquitin complex associated with sarcomeric actin in muscle fibers in early stages of intoxication. Based on these results it seems that actin is an important target in organophosphate-induced myofiber degradation and that the degradation of this protein-by the polyubiquitin pathway-may play an important role in the early disorganization of the sarcomere, as observed by electron microscopy. A possible role of the ubiquitin proteolytic pathway is that of trying to eliminate proteins modified in the early phases of muscle fiber degeneration, which is a necessary step for regeneration of the posterior segmental muscle.

Sarcoplasmic lipase and non-specific esterase inhibition in myofibers of rats intoxicated with the organophosphate isofenphos.

The expression of sarcoplasmic esterases, lipases as well as the lipid content in the myofibers of the diaphragm of rats intoxicated with the organophosphate isofenphos was studied. Lipid accumulation was documented at light, electron microsopic and by morphometric studies. The distribution of these lipid droplets was irregular and abundant in myofibers with numerous mitochondria (predominantly oxidative fibers). Histochemical inhibition of sarcoplasmic esterases and lipases was observed in the intoxicated animals. This sarcoplasmic inhibition of esterases occurs roughly in parallel to the inhibition of plasma cholinesterase activity. The inhibition of sarcoplasmic lipases may explain, at least partially, the accumulation of lipids. This inhibition probably makes difficult the use of lipids as fuel, especially in the oxidative fibers. In contrast to the small amount of muscle necrosis, (1.30+/-0.745), metabolic muscle impairment was intense and extensive, i.e., decreased activities of esterases and lipases in the sarcoplasm, that should contribute to muscle weakness. Therefore, because segmental necrosis was most prominent in oxidative fibers (and these fibers use lipids as the principal fuel and contain the greater amount of lipases in the sarcoplasm), it is possible that inhibition of activity of lipases is responsible for the segmental necrosis. Although the exact role of these metabolic changes is not known, it is possible that they contribute not only to the induction and evolution of muscle cell necrosis but also to the muscle weakness and clinical impairment of animals and humans in the acute intoxication by these compounds.

Protective effect of pralidoxime on muscle fiber necrosis induced by organophosphate compounds.

OBJECTIVE: 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.

Evaluation of the role of formulation on parathion toxicity.

The influence of the vehicle on the toxicity of parathion was evaluated by determining the oral and dermal LD50 in rats. The assessment of dermal absorption was performed by measuring the inhibition of plasma cholinesterase activity. The test vehicles were arol and xylene. The data obtained indicated that the acute oral and dermal toxicities are higher in xylene than in arol, but no differences were observed on plasma cholinesterase activity.

[Organophosphate-induced myotoxicity]. / Miotoxicidade por organofosforados.

Organophosphates comprise a group of chemical compounds extensively used in farming as insecticides, which cause accidental poisoning in animals and men and are also used in suicide attempts. The toxicity of these compounds is due especially to the cardiac and respiratory impairment in consequence of autonomic nervous system disorders. However, it is known that some of these products induce a myopathy in experimental animals and humans. This myopathy is characterized by muscle cell degeneration, involving above all the respiratory muscles. Based on the fact that this involvement certainly enhances the respiratory impairment, this study offers an experimental method for routine evaluation of organophosphate myotoxicity, using a minimal and sufficient battery of stains and histochemical reactions, for muscle necrosis quantification. For this purpose, albino rats (Wistar) treated with the organophosphate paraoxon, were used both with and without antidotes (atropine or pralidoxime). Muscle fiber necrosis in the diaphragm of the rats treated with paraoxon or paraoxon and atropine, that affected about 15% of the fibers in some areas, was detected. In the group treated with paraoxon and pralidoxime, a minimal necrosis was seen, revealing a protective role of this later antidote during the development of myopathy.

International safety assessment of pesticides: dithiocarbamate pesticides, ETU, and PTU--a review and update.

For the last 30 years the Joint FAO/WHO Meeting on Pesticide Residues (JMPR) has carried out toxicological evaluations and safety assessments of dithiocarbamate pesticides, continuously adjusting previous appraisals in the light of new data and advances in the understanding of the principles and mechanisms of toxic action of these compounds. The historical narrative of the evaluative process is followed by an account of the present international safety assessment status of the dithiocarbamate pesticides so far examined by the JMPR. They are ferbam, mancozeb, maneb, metiram, nabam, propineb, thiram, zineb, ziram, and the associated substances, ethylenethiourea (ETU) and propylenethiourea (PTU).

Changes in myelinated nerve fibers and skeletal muscle of rats exposed to high doses of permethrin.

Neurological signs and segmental demyelination in a cervical nerve were observed in rats treated orally with permethrin (300 mg/kg/day) for 5 days. Inflammatory and degenerative signals were recorded in the diaphragm muscle. These effects were more intense with the trade grade than with the technical grade product. The possible influence of the percentage of cis:trans isomers on the intensity of the observed effects is discussed.

Effects of phenobarbital, chlordane, and oxytetracycline on DDT excretion in rats.

The effects of phenobarbital, chlordane, and oxytetracycline on DDT biliary excretion in rats were evaluated. The relationship between the increase of biliary flow induced by these drugs and the elimination of DDT was also evaluated. Phenobarbital (2.5 mg/ml) was fed to rats in their drinking water and chlordane (200 mg/kg) was added to the diet over a period of 3 days; oxytetracycline (200 mg/kg/day) was fed to rats orally for 8 days. After these treatments [14C]DDT was administered orally to anesthetized rats and then the bile was collected through cannulation of the bile duct. The data obtained show that phenobarbital and chlordane decrease zoxazolamine paralysis time and increase liver weight and biliary flow. Both drugs increase biliary excretion of [14C]DDT and decrease [14C]DDT levels in plasma; oxytetracycline increases zoxazolamine flow significantly. Oxytetracycline does not change biliary excretion of [14C]DDT but decreases the blood levels of the insecticide; and pretreatment of animals with phenobarbital, chlordane, and oxytetracycline does not significantly change [14C]DDT concentration in bile. These data demonstrate that the increased biliary excretion of DDT depends on the rate of bile elimination.

Short-term effect of malathion on rats' blood glucose and on glucose utilization by mammalian cells in vitro.

Blood glucose increased in rats treated with a single ip dose of malathion (650 mg/kg). This effect was observed in the first hour of treatment, reached a 2.2-fold peak after 2 hr, and decreased after 4 hr. Malathion (20 micrograms/ml) caused a decrease of glucose utilization in IB-RS-2 cells treated for 8 hr. This effect was observed as early as 30 min after treatment and was time-dependent.

Atividades das fosfatases acida e alcalina em celulas cultivadas in vitro expostas ao DDT. / Activities of acid and alkaline phosphatases in vitro cultured cells exposed to DDT

As atividades das fosfatoses acida e alcalina foram determinadas em celulas IB-RS-2 e CHO tratadas com DDT (20,0 micrograma/ml) por um periodo de 24 horas. Verificou-se que o DDT aumenta a atividade da fosfatase acida, efeito que e mais acentuado nas celulas IB-RS-2 do que nas celulas CHO.O DDT tambem aumenta a atividade da fosfatase alcalina, porem em niveis semelhantes, nos dois sistemas celulares

[Effects of DDT and aldrin on swine cell line IB-RS-2]. / Effeitos do DDT e do aldrin em células da linhagem suína IB-RS-2.

Swine cells IB-RS-2 were exposed to 0,1-100 microgram/ml medium of DDT and aldrin for 48 hours. The data obtained showed that both compounds decreased cell growth. This effect depends on the concentration and on the time of cell exposition to the insecticides. These compounds also decreased the levels of cellular protein, RNA and DNA. The degrees of changes with aldrin were less than with DDT.

[Effects of the organophosphorus insecticide Ofunack on the metabolism of cells cultured in vitro]. / Efeitos do inseticida fosforado, "ofunack" sobre o metabolismo de células cultivadas "in vitro".

The effects of "ofunack (0,0-diethyl-0-(3-oxo-2-phenyl-2H-pyridazine-6-y1) phosphorothionate on the metabolism of IB-RS-2 cell line were studied. "Ofunack" stimulates cell growth and protein synthesis till 24 hours after its addition to the maintenance medium. Otherwise after this time "ofunack" induces an inhibition both on cell growth and on protein synthesis. This insecticide also inhibits the synthesis of RNA and DNA.