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S D Murphy

Publications and source records attributed to S D Murphy.

At least 37 records · Page 2Linked to original sources
PubMed1986

Conditioned taste aversion induced by organophosphate compounds in rats.

Three organophosphate compounds, dichlorvos, parathion and diisopropylfluorophosphate were tested as an unconditioned stimulus in the conditioned taste aversion (CTA) test. All organophosphates caused a dose-dependent CTA in rats at doses which did not induce any other signs of toxicity. Experiments with dichlorvos showed that the minimum dose which caused CTA did not alter the rats' sensitivity to pain or their behavior in either an open field or an inclined plane. Cholinesterase activity was inhibited in a dose-dependent manner in brain and plasma after administration of the organophosphates and CTA was correlated with the degree of plasma cholinesterase inhibition. CTA appears to be a sensitive indicator of neurobehavioral effects of mild exposure to organophosphates which causes only 30-40% inhibition of plasma cholinesterase.

Analgesics↗
PubMed1986

Carbachol- and norepinephrine-stimulated phosphoinositide metabolism in rat brain: effect of chronic cholinesterase inhibition.

Activation of cholinergic muscarinic receptors leads to several biochemical events including an increased turnover of phosphoinositides. In this study we have investigated whether repeated administration of the organophosphorus insecticide disulfoton, known to cause the development of tolerance to this compound, would affect phosphoinositide metabolism in rat brain. Basal and carbachol-stimulated phosphoinositide metabolism were measured in cerebral cortex slices, by measuring the accumulation of inositol phosphates (InsPs) in the presence of lithium. In control animals carbachol caused a 600% increase in InsPs accumulation with an EC50 of 100 microM. Maximal effect occurred with a LiCl concentration of 7.5 mM and required the presence of calcium. Administration of disulfoton for 10 days (2 mg/kg/day by gavage), decreased the number of muscarinic receptors in cortex from 1.1 to 0.7 pmol/mg of protein without changing the affinity of the receptors (both measured by binding of [3H]quinuclidinyl benzilate). Acetylcholinesterase was inhibited by 85%. Basal InsPs accumulation was unchanged in disulfoton-treated rats, whereas carbachol-stimulated InsPs accumulation decreased by 18%. No changes of norepinephrine-stimulated InsPs formation and of alpha-1 adrenoceptors were present in cortices from disulfoton-treated rats. Recovery of muscarinic receptor binding and carbachol-stimulated InsPs accumulation occurred at a similar rate and was completed 2 to 3 weeks after the end of the treatment, whereas acetylcholinesterase activity was still 38% inhibited 3 weeks later. These results support the hypothesis that a functional adaptation of muscarinic receptors is involved in the development of tolerance to organophosphates.

Acetylcholinesterase↗
PubMed1985

Characterization of muscarinic cholinergic receptors in the submandibular gland of the rat.

The specific muscarinic ligand [3H]quinuclidinyl benzilate ([3H]QNB) was used to label acetylcholine receptors in the submandibular gland of the rat. Specific binding of [3H]QNB increased linearly with tissue concentration in the range of 0.02-0.3 mg of protein/ml. Kinetic analysis of [3H]QNB binding revealed the presence of a single population of high affinity binding sites, with a dissociation constant of 87.2 pM and a Hill coefficient of 0.95. The binding was saturable and the receptor density was 214 fmol/mg of protein. The rate constants at 37 degrees C for association and dissociation of the [3H]QNB-receptor complex were 5.98 X 10(-8) M-1 X min-1 and 6.6 X 10(-3) X min-1, respectively. The ratio k-1/k+1 gave a Kd value of 11.1 pM, similar to the Kd value (13.1 pM) determined by kinetic parameters when extrapolated at infinitely low receptor concentration. Muscarinic antagonists displaced [3H]QNB from muscarinic receptors with a Hill coefficient near to 1.0. Displacement curves for muscarinic agonists and for the atypical antagonist pirenzepine had Hill values significantly less than one. In the presence of 0.1 mM GPP(NH)P, the potency of agonists but not antagonists in displacing [3H]QNB binding decreased 2 to 3-fold. The [3H]QNB binding site was sensitive to the inhibitory effect of various sulfhydryl reagents. Repeated treatments of rats with an acetylcholinesterase inhibitor led to a decreased density of muscarinic receptors in the submandibular gland. This alteration was specific for the muscarinic recognition site and was paralleled by a reduced sensitivity to carbachol.

Animals↗
PubMed1985

Metabolic activation of phosphorothioate pesticides: role of the liver.

Mouse liver perfusion studies in situ revealed that the cholinesterase inhibitor chlorpyrifos oxon produced by the liver from the phosphorothioate pesticide chlorpyrifos was quickly detoxified within the liver, thereby preventing it's exit from the liver in the effluent. In contrast, when the pesticide parathion was perfused as a substrate a substantial amount of the toxic metabolite paraoxon was found in exiting perfusate. Pesticide concentrations (5-15 microM) used in the perfusion studies in situ were similar to their hepatic portal blood concentrations in vivo (2.32-12.95 microM) after i.p. administration of lethal or near lethal doses. Moreover, the half-life for elimination of paraoxon by mouse blood in vitro was 8.6 min, a rate sufficiently low to allow passage of paraoxon to extrahepatic target tissues from liver in vivo. These results suggest that in the mouse, the acute toxicity of chlorpyrifos is mediated by extrahepatic production of oxon, whereas that of parathion is likely mediated by both hepatic and extrahepatic activation.

Animals↗
PubMed1984

The role of hepatic biotransformation in mediating the acute toxicity of the phosphorothionate insecticide chlorpyrifos.

The apparent (app) Km and app Vmax for mouse hepatic microsomal oxidative detoxification of chlorpyrifos to 3,5,6-tricholoro-2-pyridinol were 16.10 +/- 6.8 microM and 263.2 +/- 22.5 nmol/liver/min, respectively. The app Km and app Vmax for the oxidative activation of chlorpyrifos to chlorpyrifos oxon were 20.0 +/- 6.5 microM and 126.1 +/- 14.6 nmol/liver/min, respectively, whereas the app Km and app Vmax for hepatic microsomal hydrolysis of chlorpyrifos oxon to 3,5,6-trichloro-2-pyridinol were 1.87 +/- 0.36 mM and 89,450.7 +/- 12,087.3 nmol/liver/min, respectively. Under first-order conditions the capacity of mouse hepatic microsomes to detoxify chlorpyrifos oxon exceeded their capacity to generate this potent cholinesterase inhibitor from chlorpyrifos by a factor of 7.6. Pretreatment of mice with phenobarbital (70 mg/kg daily for 4 days) resulted in a 2.5-fold increase in the app Vmax's for oxidative activation and detoxification of chlorpyrifos, and a 1.6-fold increase in the app Vmax for hydrolysis of chlorpyrifos oxon. The app Km's were not altered by phenobarbital pretreatment. Administration of beta-naphthoflavone (80 mg/kg/daily for 2 days) to mice resulted in a slight decrease in the app Vmax's for oxidative activation and detoxification of chlorpyrifos, without altering the app Km's of the same reactions, or the hydrolysis of chlorpyrifos oxon. Phenobarbital and beta-naphthoflavone increased and decreased, respectively, the predicted hepatic clearance of chlorpyrifos. The acute toxicity of chlorpyrifos was slightly antagonized by phenobarbital pretreatment, but was potentiated by beta-naphthoflavone administration. These pretreatments did not affect cholinesterase, nonspecific esterase, or plasma A-esterase activities. Collectively, these results suggest that chlorpyrifos oxon formed within the liver does not escape hydrolysis by the liver, and that extrahepatic sites of activation are important in directly mediating the acute toxicity of chlorpyrifos.

Animals↗
PubMed1984

Chronic administration of an organophosphorus insecticide to rats alters cholinergic muscarinic receptors in the pancreas.

Male rats were treated for 10 days with the organophosphorus insecticide, acetylcholinesterase inhibitor, O,O-diethyl S-[2-(ethylthio)ethyl] phosphorodithioate (disulfoton, 2 mg/kg/day by gavage). At the end of the treatment, binding of [3H]quinuclidinyl benzilate ( [3H]QNB) to cholinergic muscarinic receptors and cholinesterase (ChE) activity were assayed in the pancreas. Functional activity of pancreatic muscarinic receptor was investigated by determining carbachol-stimulated secretion of alpha-amylase in vitro. ChE activity and [3H]QNB binding were significantly decreased in the pancreas from disulfoton-treated rats. The alteration of [3H]QNB binding was due to a decrease in muscarinic receptor density with no change in the affinity. Basal secretion of amylase from pancreas in vitro was not altered, but carbachol-stimulated secretion was decreased. The effect appeared to be specific since pancreozymin was able to induce the same amylase release from pancreases of control and treated rats. The results suggest that repeated exposures to sublethal doses of an organophosphorus insecticide lead to a biochemical and functional alteration of cholinergic muscarinic receptors in the pancreas.

Animals↗
PubMed1984

Mixed-function oxidase studies in the redfish, Sciaenops ocellata, from Galveston Bay, Texas.

The metabolism of parathion to para-nitrophenol (PNP) in redfish (Sciaenops ocellata) liver microsomes has been both identified and characterized. This mixed-function oxidase (MFO) reaction in redfish requires NADPH and is inhibited by carbon monoxide. It exhibits a temperature optimum of 25 degrees C but no clear pH optimum between 7.0-8.5. Redfish hepatic microsomal MFOs were not induced by 2.5 days after a single i.p. injection of 88 mg Aroclor 1254/kg body wt, but under the same dosage and time conditions male albino Swiss mice were significantly induced (p less than 0.05).

Animals↗
PubMed1984

The interaction of the phosphorothioate insecticides chlorpyrifos and parathion and their oxygen analogues with bovine serum albumin.

The distribution and subsequent toxicity of hazardous chemicals can be influenced by their interactions with plasma proteins. In the present study reversible binding of the phosphorothioate insecticides chlorpyrifos and parathion to fatty acid-free bovine serum albumin (BSA) was examined using the technique of equilibrium dialysis. Computer analyses of the binding data revealed that chlorpyrifos and parathion each bound reversibly to a single class of binding sites on BSA, with apparent KD values of 3.4 +/- 0.1 and 11.1 +/- 0.3 microM, respectively. Additionally, the maximal number of binding sites for each insecticide per molecule of BSA was one. Displacement studies using both chlorpyrifos and parathion indicated that each was a competitive inhibitor of the other's binding, suggesting that they were bound to the same site. Incubation of chlorpyrifos oxon or paraoxon with a 1% solution of BSA resulted in limited, EDTA-insensitive formation of 3,5,6-trichloro-2-pyridinol or p-nitrophenol, respectively. Pretreatment of BSA with 5 mM paraoxon, chlorpyrifos oxon, or 1 mM diisopropylfluorophosphate did not alter this activity, suggesting that these reactions resulted from an esterase-like capacity of BSA, and not from phosphorylation of BSA by these oxons.

Animals↗
PubMed1984

Interaction between acetaminophen and organophosphates in mice.

This study was undertaken to investigate whether depletion of hepatic nonprotein sulfhydryls (NPSH) by acetaminophen would potentiate the toxicity of organophosphates which are detoxified by glutathione transferases. Acetaminophen caused a dose dependent decrease of NPSH in mouse liver. At the dose of 600 mg/kg, which decreased hepatic NPSH by 90%, acetaminophen did not potentiate the effects of the organophosphorus insecticides methylchlorpyrifos, methylparathion or dichlorovos on esterases. On the other hand, depletion of hepatic NPSH by diethylmaleate increased the toxicities of the insecticides. While the reported inhibition of mixed function oxidase activity by acetaminophen may explain the lack of potentiation of methylchlorpyrifos and methylparathion which need to be converted to their oxygen analogs, its failure in potentiating the toxicity of dichlorvos, which does not require metabolic activation, suggests that other mechanisms are involved. The finding that acetaminophen decreased NPSH only in the liver and, to a minor extent, in the kidney, while diethylmaleate caused significant depletion of NPSH in several tissues, suggests that extrahepatic glutathione may be relevant to the detoxication of certain organophosphates.

Acetaminophen↗
PubMed1984

Antinociceptive effect of the GABAmimetic 4,5,6,7-tetrahydroisoxazolo [5, 4-c]pyridin-3-ol (THIP): chronic treatment increases alpha-2 adrenoceptors in the mouse brain.

It has been shown that the gamma-aminobutyric acid mimetic THIP (4,5,6,7-tetrahydroisoxazolo [5,4-c] pyridin-3-ol) has an antinociceptive effect in the mouse. Repeated administrations of THIP induced the development of tolerance to its antinociceptive effect. An increased binding of [3H]clonidine to alpha-2 adrenoceptors was found in the cerebral cortex of THIP-tolerant mice, due to an increase of receptor density. This alteration was not present after acute treatment with THIP and was specific for alpha-2 adrenergic receptors, as alpha-1 and beta adrenergic, muscarinic and gamma-aminobutyric acid receptors were unchanged in THIP-tolerant mice. Animals tolerant to THIP were also super-sensitive to the antinociceptive effect of clonidine. The alpha-2 adrenergic receptor antagonist yohimbine antagonized THIP-induced antinociception. These results suggest that the noradrenergic system may be involved in THIP antinociception and in the development of tolerance.

Analgesics↗
PubMed1983

Muscarinic receptor alterations as a mechanism of anticholinesterase tolerance.

Tolerance to the toxic signs of the organophosphorus ester acetylcholinesterase inhibitor, O,O-diethyl S-[2-(ethylthio)ethyl] phosphorodithioate (disulfoton), was induced in rats by giving 10 doses of 2.0 mg/kg/day. Concurrent with the induction of tolerance, decreased sensitivity to the cholinergic agonists carbachol and oxotremorine could be demonstrated in studies of heart rate in vivo and in isolated preparations of ileum and atria. A significant decrease in the binding of the muscarinic antagonist [3H]quinuclidinyl benzilate could be demonstrated in ileum from disulfoton-tolerant animals. However, no alterations in the binding of [3H]quinuclidinyl benzilate, [3H]oxotremorine-M, or oxotremorine were evident in atria from tolerant animals. The results suggest that, in addition to receptor loss, other mechanisms distal to ligand recognition sites or removed from the receptor complex may contribute to the subsensitivity of tissues to muscarinic cholinergic agonists.

Animals↗
PubMed1983

Effect of trimethyltin on hepatic and extra-hepatic non-protein sulfhydryl levels in the mouse.

Administration of trimethyltin (TMT) ip to mice lowered non-protein sulfhydryl (NPSH) levels in a tissue-specific and dose-dependent manner. Incubation of TMT with GSH and mouse hepatic cytosol did not result in conjugation of TMT, as evidenced by the lack of reduction of GSH levels. Additionally, TMT in vivo did not increase oxidized glutathione (GSSG) levels, nor did it alter hepatic ATP content. These results suggest that TMT decreased NPSH levels in vivo by either directly inhibiting GSH synthesis or by inhibiting uptake of precursor amino acids.

Animals↗
PubMed1983

Distribution of trimethyltin in various tissues of the male mouse.

Trimethyltin (TMT) levels were determined in various tissues of male mice at 1, 2, 4, 6, 10 and 16 h after administration (4.26 mg/kg; i.p.). Peak TMT levels in kidneys, liver, blood, lungs and testes were observed at 1 h following administration. Penetration into the brain, skeletal muscle and adipose tissue was also observed where maximum TMT levels were achieved 6-16 h following administration. 16 h post-treatment, the order of mean tissue concentrations, of the compound was: liver greater than testes greater than kidneys greater than lungs greater than brain greater than skeletal muscle greater than adipose tissue greater than blood. TMT was retained at peak levels in most tissues until, by 16 h, the animals exhibited tremors and convulsions followed by death. The mean concentration of TMT in the brain associated with delayed (central nervous system) (CNS) excitability at 16 h was 1.53 micrograms/g of wet tissue. These results indicate that TMT rapidly distributes and, although water-soluble, persists in tissues following an i.p. administration.

Adipose Tissue↗
PubMed1983

[3H]Nicotine binding in rat brain: alteration after chronic acetylcholinesterase inhibition.

(+/-)-[3H]Nicotine binds specifically to rat brain membranes. The binding is stereospecific, (+)-nicotine being 57 times less potent than (-)-nicotine in displacing labeled (+/-)-nicotine. Saturation binding experiments revealed the presence of two binding sites with dissociation constant (Kd) values of 23.7 and 590 nM, and binding site density (Bmax) values of 76 and 646 fmol/mg of protein, respectively. The substrate specificity of the binding site suggests that it represents the nicotinic cholinergic receptor. [3H] Nicotine binding was found to be highest in the hypothalamus and hippocampus and lowest in the cerebellum. Chronic treatment with the acetylcholinesterase inhibitor disulfoton (2 mg/kg/day for 10 days) decreased the number of cholinergic muscarinic and nicotinic binding sites in rat brain. Moreover, the antinociceptive effect of nicotine was found to be markedly reduced in rats chronically treated with disulfoton.

Acetylcholinesterase↗
PubMed1982

Differential alterations of cholinergic muscarinic receptors during chronic and acute tolerance to organophosphorus insecticides.

Male mice treated for 2 weeks with the anticholinesterase insecticide disulfoton (O,O-diethyl S-[2-(ethylthio)-ethyl] phosphorodithioate; 10 mg per kg per day) became tolerant to the hypothermic and antinociceptive effects of disulfoton itself and of oxotremorine, a muscarinic cholinergic agonist. Homogenates of brain and ileum from tolerant animals exhibited reduced binding of the specific muscarinic antagonist [3H]quinuclidinyl benzilate ([3H]QNB). In forebrains of tolerant animals, the number of receptors (Bmax) was decreased 40% with no change in the affinity constant. Acetylcholinesterase (AChE) activity was 15% of control. Forty-eight hours after a single injection of disulfoton (10 mg/kg) mice were more resistant than their controls to the hypothermic and antinociceptive effects of a second administration of the same insecticide and of oxotremorine. Tolerance was not present 96 hr after a single administration of disulfoton. A single injection of disulfoton produced 74, 65 and 27% inhibition of AChE activity after 4, 48 and 96 hr respectively. Four hours after a second injection at 49 and 96 hr, 73 or 72% inhibition was found. [3H]QNB binding of animals treated with a single injection of disulfoton and of controls did not differ at either time point. An increase in the Ki for inhibition of [3H]QNB binding by unlabeled oxotremorine was observed in forebrain from mice killed 48 hr after a single injection of disulfoton, indicating a decreased affinity of the muscarinic receptor for agonists. Binding of [3H]oxotremorine-M was decreased significantly 48 hr after a single injection of disulfoton and after chronic treatment. It is suggested that a differential down-regulation of muscarinic receptors occurs in acute and chronic tolerance, involving agonist and antagonist binding sites and depending on duration of exposure.

Acetylcholinesterase↗