Mechanism of preservation of the intestinal mucosa architecture and NF-κB/PGE2 reduction by hydrogen sulfide on cholera toxin-induced diarrhea in mice.

AIMS: Investigate the involvement of Hydrogen sulfide (H2S) in inflammatory parameters and intestinal morphology caused by cholera toxin (CT) in mice. MAIN METHODS: Mice were subjected to the procedure of inducing diarrhea by CT in the isolated intestinal loop model. The intestinal loops were inoculated with H2S donor molecules (NaHS and GYY 4137) or saline and CT. To study the role of EP2 and EP4 prostaglandin E2 (PGE2) receptors in the H2S antisecretory effect, PAG (DL-propargylglycine - inhibitor of cystathionine-γ-lyase (CSE)), PF-04418948 (EP2 antagonist) and ONO-AE3-208 (EP4 antagonist) were used. The intestinal loops were evaluated for intestinal secretion, relation of the depth of villi and intestinal crypts, and real-time PCR for the mRNA of the CXCL2, IL-6, NOS-2, IL-17, NF-κB1, NF-κBIA, SLC6A4 and IFN-γ genes. KEY FINDINGS: H2S restored the villus/crypt depth ratio caused by CT. NaHS and GYY 4137 increased the expression of NF-κB1 and for the NF-κBIA gene, only GYY 4137 increased the expression of this gene. The increased expression of NF-κB inhibitors, NF-κB1 and NF-κBIA by H2S indicates a possible decrease in NF-κB activity. The pretreatment with PAG reversed the protective effect of PF-04418948 and ONO-AE3-208, indicating that H2S probably decreases PGE2 because in the presence of antagonists of this pathway, PAG promotes intestinal secretion. SIGNIFICANCE: Our results point to a protective activity of H2S against CT for promoting a protection of villus and crypt intestine morphology and also that its mechanism occurs at least in part due to decreasing the activity of NF-κB and PGE2.

Reactivation of VX-Inhibited Human Acetylcholinesterase by Deprotonated Pralidoxime. A Complementary Quantum Mechanical Study.

In the present work, we performed a complementary quantum mechanical (QM) study to describe the mechanism by which deprotonated pralidoxime (2-PAM) could reactivate human (Homo sapiens sapiens) acetylcholinesterase (HssAChE) inhibited by the nerve agent VX. Such a reaction is proposed to occur in subsequent addition-elimination steps, starting with a nucleophile bimolecular substitution (SN2) mechanism through the formation of a trigonal bipyramidal transition state (TS). A near attack conformation (NAC), obtained in a former study using molecular mechanics (MM) calculations, was taken as a starting point for this project, where we described the possible formation of the TS. Together, this combined QM/MM study on AChE reactivation shows the feasibility of the reactivation occurring via attack of the deprotonated form of 2-PAM against the Ser203-VX adduct of HssAChE.

Resistance profile and molecular characterization of pyrethroid resistance in a Rhipicephalus microplus strain from Colombia.

Intensive use of chemical acaricides for the control of cattle ticks (Rhipicephalus microplus) has led to the development of multiple acaricide resistance in Colombia. The present study aimed to characterize, using toxicological bioassays and molecular biology techniques, the resistance profile of a tick strain isolated from the Arauca state, Northeast Colombia. Commercial acaricides were used in adult immersion tests to determine its in vitro efficacies. Deltamethrin showed very low activity (4-7.3%), a mixture of cypermethrin and chlorpyrifos had intermediate efficacy (64-75.2%), and ethion presented the highest activity (88.5-100%). A colony (Arauquita strain) was established and larval immersion tests confirmed high resistance level to deltamethrin (241-fold) and susceptibility to ivermectin. A quantitative polymerase chain reaction-high resolution melt technique was used to identify single nucleotide polymorphisms (SNPs) in the para-sodium channel gene. All of the genotyped individuals were mutant, presenting one (n = 7), two (n = 7) or three (n = 9) SNPs previously associated with pyrethroid resistance. Sequencing revealed a novel mutation (F712L), that was found for the first time in R. microplus ticks from South America. This is the first description of mutations associated with pyrethroid resistance in R. microplus from Colombia. The acaricide resistance pattern found in the Arauquita strain is similar to other parts of Colombia.

Effects of fast versus slow-releasing hydrogen sulfide donors in hypertension in pregnancy and fetoplacental growth restriction.

Hydrogen sulfide (H2S) is a vasorelaxant gas with therapeutic potential in several diseases. However, effects of H2S donors in hypertensive pregnancy complicated by feto-placental growth restriction are unclear. Therefore, we aimed to examine and compare the effects of fast-releasing H2S donor (sodium hydrosulfide-NaHS) and slow-releasing H2S donor (GYY4137) in hypertension-in-pregnancy. Pregnant rats were distributed into four groups: normal pregnancy (Norm-Preg), hypertensive pregnancy (HTN-Preg), hypertensive pregnancy + NaHS (HTN-Preg + NaHS), and hypertensive pregnancy + GYY4137 (HTN-Preg + GYY). Systolic blood pressure, plasma H2S levels, fetal and placental weights, number of viable fetuses, litter size, and endothelium-dependent vasodilation were examined. Also, oxidative stress was assessed in placenta. We found that GYY4137 attenuated hypertension on gestational days 16 and 18, while NaHS presented antihypertensive effect only on gestational day 18. GYY4137, but not NaHS, increased plasma H2S levels. Greater fetal and placental weights were found with GYY4137 than NaHS treatment. Also, HTN-Preg + NaHS presented further reductions in placental weights when compared to HTN-Preg group. Number of viable fetuses and litter size presented no significant changes. GYY4137 reduced placental oxidative stress caused by hypertension, while greater increases in oxidative stress were found in HTN-Preg + NaHS than HTN-Preg group. Hypertensive pregnancy caused impaired endothelium-dependent vasodilation, while GYY4137 and NaHS treatments blunted endothelial dysfunction. Endothelium-dependent vasodilation was completely blocked by the nitric oxide synthase inhibitor. We conclude that slow-releasing H2S donor GYY4137 is advantageous compared with fast-releasing H2S-donor NaHS to attenuate hypertension-in-pregnancy and to protect against feto-placental growth restriction and oxidative stress.

Molecular modeling studies on the interactions of 7-methoxytacrine-4-pyridinealdoxime, 4-PA, 2-PAM, and obidoxime with VX-inhibited human acetylcholinesterase: a near attack conformation approach.

7-methoxytacrine-4-pyridinealdoxime (7-MEOTA-4-PA, named hybrid 5C) is a compound formerly synthesized and evaluated in vitro, together with 4-pyridine aldoxime (4-PA) and commercial reactivators of acetylcholinesterase (AChE). This compound was designed with the purpose of being a prophylactic reactivator, capable of interacting with different subdomains of the active site of AChE. To investigate these interactions, theoretical results from docking were first compared with experimental data of hybrid 5C, 4-PA, and two commercial oximes, on the reactivation of human AChE (HssAChE) inhibited by VX. Then, further docking studies, molecular dynamics simulations, and molecular mechanics Poisson-Boltzmann surface area calculations, were carried out to investigate reactivation performances, considering the near attack conformation (NAC) approach, prior to the nucleophilic substitution mechanism. Our results helped to elucidate the interactions of such molecules with the different subdomains of the active site of HssAChE. Additionally, NAC poses of each oxime were suggested for further theoretical studies on the reactivation reaction.

The organophosphate pesticide methamidophos opens the blood-testis barrier and covalently binds to ZO-2 in mice.

Methamidophos (MET) is an organophosphate (OP) pesticide widely used in agriculture in developing countries. MET causes adverse effects in male reproductive function in humans and experimental animals, but the underlying mechanisms remain largely unknown. We explored the effect of MET on mice testes (5 mg/kg/day/4 days), finding that this pesticide opens the blood-testis barrier and perturbs spermatogenesis, generating the appearance of immature germ cells in the epididymis. In the seminiferous tubules, MET treatment changed the level of expression or modified the stage-specific localization of tight junction (TJ) proteins ZO-1, ZO-2, occludin, and claudin-3. In contrast, claudin-11 was barely altered. MET also modified the shape of claudin-11, and ZO-2 at the cell border, from a zigzag to a more linear pattern. In addition, MET diminished the expression of ZO-2 in spermatids present in seminiferous tubules, induced the phosphorylation of ZO-2 and occludin in testes and reduced the interaction between these proteins assessed by co-immunoprecipitation. MET formed covalent bonds with ZO-2 in serine, tyrosine and lysine residues. The covalent modifications formed on ZO-2 at putative phosphorylation sites might interfere with ZO-2 interaction with regulatory molecules and other TJ proteins. MET bonds formed at ZO-2 ubiquitination sites likely interfere with ZO-2 degradation and TJ sealing, based on results obtained in cultured epithelial cells transfected with ZO-2 mutated at a MET target lysine residue. Our results shed light on MET male reproductive toxicity and are important to improve regulations regarding the use of OP pesticides and to protect the health of agricultural workers.

Protective effects of exogenous and endogenous hydrogen sulfide in mast cell-mediated pruritus and cutaneous acute inflammation in mice.

The recently described 'gasomediator' hydrogen sulfide (H2S) has been involved in pain mechanisms, but its effect on pruritus, a sensory modality that similarly to pain acts as a protective mechanism, is poorly known and controversial. The effects of the slow-releasing (GYY4137) and spontaneous H2S donors (Na2S and Lawesson's reagent, LR) were evaluated in histamine and compound 48/80 (C48/80)-dependent dorsal skin pruritus and inflammation in male BALB/c mice. Animals were intradermally (i.d.) injected with C48/80 (3µg/site) or histamine (1µmol/site) alone or co-injected with Na2S, LR or GYY4137 (within the 0.3-100nmol range). The involvement of endogenous H2S and KATP channel-dependent mechanism were also evaluated. Pruritus was assessed by the number of scratching bouts, whilst skin inflammation was evaluated by the extravascular accumulation of intravenously injected 125I-albumin (plasma extravasation) and myeloperoxidase (MPO) activity (neutrophil recruitment). Histamine or C48/80 significantly evoked itching behavior paralleled by plasma extravasation and increased MPO activity. Na2S and LR significantly ameliorated histamine or C48/80-induced pruritus and inflammation, although these effects were less pronounced or absent with GYY4137. Inhibition of endogenous H2S synthesis increased both Tyrode and C48/80-induced responses in the skin, whereas the blockade of KATP channels by glibenclamide did not. H2S-releasing donors significantly attenuate C48/80-induced mast cell degranulation either in vivo or in vitro. We provide first evidences that H2S donors confer protective effect against histamine-mediated acute pruritus and cutaneous inflammation. These effects can be mediated, at least in part, by stabilizing mast cells, known to contain multiple mediators and to be primary initiators of allergic processes, thus making of H2S donors a potential alternative/complementary therapy for treating inflammatory allergic skin diseases and related pruritus.

Hydrogen sulfide donors alleviate itch secondary to the activation of type-2 protease activated receptors (PAR-2) in mice.

Hydrogen sulfide (H2S) has been highlighted as an endogenous signaling molecule and we have previously found that it can inhibit histamine-mediated itching. Pruritus is the most common symptom of cutaneous diseases and anti-histamines are the usual treatment; however, anti-histamine-resistant pruritus is common in some clinical settings. In this way, the involvement of mediators other than histamine in the context of pruritus requires new therapeutic targets. Considering that the activation of proteinase-activated receptor 2 (PAR-2) is involved in pruritus both in rodents and humans, in this study we investigated the effect of H2S donors on the acute scratching behavior mediated by PAR-2 activation in mice, as well as some of the possible pharmacological mechanisms involved. The intradermal injection of the PAR-2 peptide agonist SLIGRL-NH2 (8-80nmol) caused a dose-dependent scratching that was unaffected by intraperitoneal pre-treatment with the histamine H1 antagonist pyrilamine (30mg/kg). Co-injection of SLIGRL-NH2 (40nmol) with either the slow-release H2S donor GYY4137 (1 and 3nmol) or the spontaneous donor NaHS (1 and 0.3nmol) significantly reduced pruritus. Co-treatment with the KATP channel blocker glibenclamide (200nmol) or the nitric oxide (NO) donor sodium nitroprusside (10nmol) abolished the antipruritic effects of NaHS; however, the specific soluble guanylyl cyclase inhibitor ODQ (30µg) had no significant effects. The transient receptor potential ankyrin type 1 (TRPA1) antagonist HC-030031 (20µg) significantly reduced SLIGRL-NH2-induced pruritus; however pruritus induced by the TRPA1 agonist AITC (1000nmol) was unaffected by NaHS. Based on these data, we conclude that pruritus secondary to PAR-2 activation can be reduced by H2S, which acts through KATP channel opening and involves NO in a cyclic guanosine monophosphate (cGMP)-independent manner. Furthermore, TRPA1 receptors mediate the pruritus induced by activation of PAR-2, but H2S does not interfere with this pathway. These results provide additional support for the development of new therapeutical alternatives, mainly intended for treatment of pruritus in patients unresponsive to anti-histamines.

Evidence of multiple/cross resistance to Bt and organophosphate insecticides in Puerto Rico population of the fall armyworm, Spodoptera frugiperda.

Fall armyworm (FAW) is a damaging pest of many economic crops. Long-term use of chemical control prompted resistance development to many insecticide classes. Many populations were found to be significantly less susceptible to major Bt toxins expressed in transgenic crops. In this study, a FAW strain collected from Puerto Rico (PR) with 7717-fold Cry1F-resistance was examined to determine if it had also developed multiple/cross resistance to non-Bt insecticides. Dose response assays showed that the PR strain developed 19-fold resistance to acephate. Besides having a slightly smaller larval body weight and length, PR also evolved a deep (2.8%) molecular divergence in mitochondrial oxidase subunit II. Further examination of enzyme activities in the midgut of PR larvae exhibited substantial decreases of alkaline phosphatase (ALP), aminopeptidase (APN), 1-NA- and 2-NA-specific esterase, trypsin, and chymotrypsin activities, and significant increases of PNPA-specific esterase and glutathione S-transferase (GST) activities. When enzyme preparations from the whole larval body were examined, all three esterase, GST, trypsin, and chymotrypsin activities were significantly elevated in the PR strain, while ALP and APN activities were not significantly different from those of susceptible strain. Data indicated that multiple/cross resistances may have developed in the PR strain to both Bt toxins and conventional insecticides. Consistently reduced ALP provided evidence to support an ALP-mediated Bt resistance mechanism. Esterases and GSTs may be associated with acephate resistance through elevated metabolic detoxification. Further studies are needed to clarify whether and how esterases, GSTs, and other enzymes (such as P450s) are involved in cross resistance development to Bt and other insecticide classes.

The hydrogen sulfide donor, Lawesson's reagent, prevents alendronate-induced gastric damage in rats.

Our objective was to investigate the protective effect of Lawesson's reagent, an H2S donor, against alendronate (ALD)-induced gastric damage in rats. Rats were pretreated with saline or Lawesson's reagent (3, 9, or 27 µmol/kg, po) once daily for 4 days. After 30 min, gastric damage was induced by ALD (30 mg/kg) administration by gavage. On the last day of treatment, the animals were killed 4 h after ALD administration. Gastric lesions were measured using a computer planimetry program, and gastric corpus pieces were assayed for malondialdehyde (MDA), glutathione (GSH), proinflammatory cytokines [tumor necrosis factor (TNF)-α and interleukin (IL)-1ß], and myeloperoxidase (MPO). Other groups were pretreated with glibenclamide (5 mg/kg, ip) or with glibenclamide (5 mg/kg, ip)+diazoxide (3 mg/kg, ip). After 1 h, 27 µmol/kg Lawesson's reagent was administered. After 30 min, 30 mg/kg ALD was administered. ALD caused gastric damage (63.35 ± 9.8 mm(2)); increased levels of TNF-α, IL-1ß, and MDA (2311 ± 302.3 pg/mL, 901.9 ± 106.2 pg/mL, 121.1 ± 4.3 nmol/g, respectively); increased MPO activity (26.1 ± 3.8 U/mg); and reduced GSH levels (180.3 ± 21.9 µg/g). ALD also increased cystathionine-γ-lyase immunoreactivity in the gastric mucosa. Pretreatment with Lawesson's reagent (27 µmol/kg) attenuated ALD-mediated gastric damage (15.77 ± 5.3 mm(2)); reduced TNF-α, IL-1ß, and MDA formation (1502 ± 150.2 pg/mL, 632.3 ± 43.4 pg/mL, 78.4 ± 7.6 nmol/g, respectively); lowered MPO activity (11.7 ± 2.8 U/mg); and increased the level of GSH in the gastric tissue (397.9 ± 40.2 µg/g). Glibenclamide alone reversed the gastric protective effect of Lawesson's reagent. However, glibenclamide plus diazoxide did not alter the effects of Lawesson's reagent. Our results suggest that Lawesson's reagent plays a protective role against ALD-induced gastric damage through mechanisms that depend at least in part on activation of ATP-sensitive potassium (KATP) channels.

The hydrogen sulfide donor, Lawesson's reagent, prevents alendronate-induced gastric damage in rats

Our objective was to investigate the protective effect of Lawesson's reagent, an H2S donor, against alendronate (ALD)-induced gastric damage in rats. Rats were pretreated with saline or Lawesson's reagent (3, 9, or 27 µmol/kg, po) once daily for 4 days. After 30 min, gastric damage was induced by ALD (30 mg/kg) administration by gavage. On the last day of treatment, the animals were killed 4 h after ALD administration. Gastric lesions were measured using a computer planimetry program, and gastric corpus pieces were assayed for malondialdehyde (MDA), glutathione (GSH), proinflammatory cytokines [tumor necrosis factor (TNF)-α and interleukin (IL)-1β], and myeloperoxidase (MPO). Other groups were pretreated with glibenclamide (5 mg/kg, ip) or with glibenclamide (5 mg/kg, ip)+diazoxide (3 mg/kg, ip). After 1 h, 27 µmol/kg Lawesson's reagent was administered. After 30 min, 30 mg/kg ALD was administered. ALD caused gastric damage (63.35±9.8 mm2); increased levels of TNF-α, IL-1β, and MDA (2311±302.3 pg/mL, 901.9±106.2 pg/mL, 121.1±4.3 nmol/g, respectively); increased MPO activity (26.1±3.8 U/mg); and reduced GSH levels (180.3±21.9 µg/g). ALD also increased cystathionine-γ-lyase immunoreactivity in the gastric mucosa. Pretreatment with Lawesson's reagent (27 µmol/kg) attenuated ALD-mediated gastric damage (15.77±5.3 mm2); reduced TNF-α, IL-1β, and MDA formation (1502±150.2 pg/mL, 632.3±43.4 pg/mL, 78.4±7.6 nmol/g, respectively); lowered MPO activity (11.7±2.8 U/mg); and increased the level of GSH in the gastric tissue (397.9±40.2 µg/g). Glibenclamide alone reversed the gastric protective effect of Lawesson's reagent. However, glibenclamide plus diazoxide did not alter the effects of Lawesson's reagent. Our results suggest that Lawesson's reagent plays a protective role against ALD-induced gastric damage through mechanisms that depend at least in part on activation of ATP-sensitive potassium (KATP) channels.

Association of methamidophos and sleep loss on reproductive toxicity of male mice.

This study investigated the effects of organophosphate exposure on the male reproductive system of mice submitted to chronic sleep loss condition. Adult Swiss mice were distributed into 4 groups: control; methamidophos (MTP); sleep restriction (SR); and MTP+SR. The dose of methamidophos was 0.002 mgkg(-1)day(-1) (half of the Acceptable Daily Intake). Sleep restriction condition was 21 h day(-1) during 15 days. In relation to control group, MTP treatment induced a significant reduction of 12% on morphologically normal spermatozoa in both MTP and MTP+SR groups. In addition, the absolute and relative weights of the seminal vesicles were decreased (MTP, -34%; MTP+SR, -45%). Epididymal fat was reduced in SR groups (SR, -64%; MTP+SR, -58%). Plasma testosterone levels were significantly decreased in MTP and SR groups, and progesterone levels were increased 8 times in MTP+SR in comparison with the control group. The corticosterone levels were unaffected by MTP or SR conditions. Thus, low dose MTP exposure resulted in deleterious effects on the male reproductive system. Sleep loss associated with MTP potentiated the effect on steroidogenesis, mainly in terms of progesterone levels.

Tools for resistance monitoring in oriental fruit moth (Lepidoptera: Tortricidae) and first assessment in Brazilian populations.

In southern Brazilian apple (Malus spp.) orchards, predominantly organophosphates are used to control the oriental fruit moth, Cydia molesta (Busck) (Lepidoptera: Tortricidae), but control failures often occur. Therefore the susceptibility of three C. molesta Brazilian populations was investigated to five insecticides of different groups and modes of action, in comparison with a susceptible laboratory strain mass reared in southern France for >10 yr. At the same time, comparative biochemical and genetic analysis were performed, assessing the activities of the detoxification enzymatic systems and sequencing a gene of insecticide molecular target to find out markers associated with resistance. The three Brazilian populations were significantly resistant to chlorpyrifos ethyl compared with the reference strain. One of the field populations that had been frequently exposed to deltamethrin treatments showed significant decreasing susceptibility to this compound, whereas none of the three populations had loss of susceptibility to tebufenozide and thiacloprid compared with the reference strain. All three populations had slight but significant increases of glutathione transferase and carboxylesterases activities and significant decrease of specific acetylcholinesterase activities compared with the reference. Only the most resistant population to chlorpyriphos exhibited a significantly higher mixed function oxidase activity than the reference. The acetylcholinesterase of females was significantly less inhibited by carbaryl in the Brazilian populations than in the reference strain (1.7-2.5-fold), and this difference was not expressed in the male moth. However, no mutation in the MACE locus was detected. These biological and molecular characterizations of adaptive response to insecticides in C. molesta provide tools for early detection of insecticide resistance in field populations of this pest.

Low concentrations of methamidophos do not alter AChE activity but modulate neurotransmitters uptake in hippocampus and striatum in vitro.

AIMS: Methamidophos (Meth) is a toxic organophosphorus compound (OP) that inhibits acetylcholinesterase enzyme (AChE) and induces neurotoxicity. As the mechanism of its neurotoxic effects is not well understood, the aim of the present study was to evaluate the effects of Meth on glutamate and gamma aminobutyric acid (GABA) uptake and correlate with cell viability and AChE and Na(+)/K(+)-ATPase enzyme activities in striatum and hippocampus slices exposed to low concentrations (0.05 to 1.0 µM) of Meth. MAIN METHODS: Hippocampal and striatal slices of rat brain were exposed to Meth for 5 min ([(3)H]Glutamate uptake) or 15 min ([(3)H]GABA uptake) for assays. The enzyme activities and cell viability were also accessed at both times in hippocampal and striatal slices and homogenates. KEY FINDINGS: At concentrations that did not inhibit AChE, Meth caused changes in glutamate uptake in striatal (0.05 and 1.0 µM Meth) and hippocampal (1.0 µM Meth) slices. GABA uptake was increased by the pesticide in striatum at 0.5 and 1.0 µM and in hippocampus at 0.05 µM. After 3.5h of Meth exposure, striatal and hippocampal cells showed no changes in viability as well as no inhibition of Na(+)/K(+)-ATPase were observed after 5 or 15 min exposure to Meth in the same brain structures. SIGNIFICANCE: Results suggest that Meth, even without changing the AChE activity can modify somehow the neurotransmitters uptake. However, further studies are necessary to clarify if this modulation in glutamate or GABA uptake may be responsible to cause some disturbance in behavior or in other neurochemical parameters following low Meth exposure in vivo.

Increases in tumor necrosis factor-alpha in response to thyroid hormone-induced liver oxidative stress in the rat.

Thyroid hormone-induced calorigenesis contributes to liver oxidative stress and promotes an increased respiratory burst activity in Kupffer cells, which could conceivably increase the expression of redox-sensitive genes, including those coding for cytokines. Our aim was to test the hypothesis that L-3,3',5-triiodothyronine (T3)-induced liver oxidative stress would markedly increase the production of TNF-alpha by Kupffer cells and its release into the circulation. Sprague-Dawley rats receive a single dose of 0.1 mg T3/kg or vehicle (controls) and determinations of liver O2 consumption, serum TNF-alpha, rectal temperature, and serum T3 levels, were carried out at different times after treatment. Hepatic content of total reduced glutathione (GSH) and biliary glutathione disulfide (GSSG) efflux were measured as indices of oxidative stress. In some studies, prior to T3 injection animals were administered either (i) the Kupffer cell inactivator gadolinium chloride (GdCl3), (ii) the antioxidants alpha-tocopherol and N-acetyl-L-cysteine (NAC), or (iii) an antisense oligonucleotide against TNF-alpha (ASO TJU-2755). T3 elicited an 80-fold increase in the serum levels of TNF-alpha at 22h after treatment, which coincided with the onset of thyroid calorigenesis. Pretreatment with GdCl3, alpha-tocopherol, NAC, and ASO TJU-2755 virtually abolished this effect and markedly reduced T3-induced liver GSH depletion and the increases in biliary GSSG efflux. It is concluded that the hyperthyroid state in the rat increases the circulating levels of TNF-alpha by actions exerted at the Kupffer cell level and these are related to the oxidative stress status established in the liver by thyroid calorigenesis.

Insecticide use and organophosphate resistance in the coffee leaf miner Leucoptera coffeella (Lepidoptera: Lyonetiidae).

Increasing rates of insecticide use against the coffee leaf minerLeucoptera coffeella(Guérin-Méneville) and field reports on insecticide resistance led to an investigation of the possible occurrence of resistance of this species to some of the oldest insecticides used against it in Brazil: chlorpyrifos, disulfoton, ethion and methyl parathion. Insect populations were collected from ten sites in the state of Minas Gerais, Brazil and these populations were subjected to discriminating concentrations established from insecticide LC99s estimated for a susceptible standard population. Eight of the field-collected populations showed resistance to disulfoton, five showed resistance to ethion, four showed resistance to methyl parathion, and one showed resistance to chlorpyrifos. The frequency of resistant individuals in each population ranged from 10 to 93% for disulfoton, 53 to 75% for ethion, 23 to 76% for methyl parathion, and the frequency of resistant individuals in the chlorpyrifos resistant population was 35%. A higher frequency of individuals resistant to chlorpyrifos, disulfoton and ethion was associated with greater use of insecticides, especially other organophosphates. This finding suggests that cross-selection, mainly between organophosphates, played a major role in the evolution of insecticide resistance in Brazilian populations of L. coffeella. Results from insecticide bioassays with synergists (diethyl maleate, piperonyl butoxide and triphenyl phosphate) suggested that cytochrome P450-dependent monooxygenases may play a major role in resistance with minor involvement of esterases and glutathione S-transferases.

Evaluation of insecticide ear tags containing ethion for control of pyrethroid resistant Haematobia irritans (L.) on dairy cattle.

A field study was conducted in central Argentina to evaluate the efficacy of ear tags containing 36% ethion against pyrethroid resistant populations of Haematobia irritans on grazing dairy cattle. The treated group consisted of 45 milking Holstein cows which received two tags per head and the control consisted of 22 dry cows from the same cohort. Treated and control groups were grazed on similar lucerne pastures separated for a minimum distance of 800 m but they were not isolated from other cattle herds on the same or contiguous properties. In both groups, horn fly estimation were made weekly by examining cattle in the pastures with the aid of binoculars. The percentage reduction of fly numbers on treated cows was considered as efficacy of control provided by the tags. The ethion ear tags provided a range of 85-99% reduction in horn fly numbers for 16 weeks. During this period, the weekly mean number of H. irritans on the tagged cows ranged between 0.44 and 28.26 compared with 143.5 and 239.1 in control animals. The ethion ear tags could be a useful tool for the control of H. irritans mainly in areas where populations of this insect have developed resistance to pyrethroid insecticides.