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Biomedical subjects

S D Murphy

Publications and source records attributed to S D Murphy.

122 records · Page 7Linked to original sources
PubMedDate not supplied

Muscarinic cholinergic binding sites on rat lymphocytes.

Receptors for neurotransmitters in blood cells could serve as useful markers for the same receptors in solid tissues. Muscarinic receptors have been identified in human, rat and mouse lymphocytes by binding of [3H]quinuclidinyl benzilate (3H-QNB); however, the biochemical and pharmacological characterization of such binding sites has not been complete. Spleen lymphocytes were isolated on a histopaque gradient and incubated in Hank's buffer with 3H-QNB. Binding of 3H-QNB was linear with increasing protein concentrations and was saturable. Binding constants were Bmax = 111 +/- 10.5 fmol/10(6) cells, and Kd = 29.7 +/- 3.9 nM (n = 7). An extensive pharmacological analysis of these binding sites indicated that several cholinergic muscarinic drugs were capable of inhibiting 3H-QNB binding. Muscarinic antagonists were more potent than agonists, and lipophilic drugs were more potent than hydrophilic drugs. Several non-cholinergic drugs were also capable of inhibiting 3H-QNB binding; however, they did so also in brain membranes, while a third group of non-cholinergic drugs and neurotransmitters were inactive. Similar results were also obtained in circulating lymphocytes and in lymphocyte membranes. These results suggest that lymphocytes possess muscarinic receptors which share several, although not all, characteristics of the same receptors in brain and other tissues. Measurement of these binding sites could be useful to monitor the status of muscarinic receptors in solid tissues.

Animals↗
PubMedDate not supplied

Behavioral and biochemical effects of postnatal parathion exposure in the rat.

Preweanling rat pups were exposed daily to parathion (1.3 mg/kg or 1.9 mg/kg) or vehicle (corn oil) on postnatal days 5-20, a time period critical to development of behavioral and biochemical parameters of the cholinergic nervous system. This exposure resulted in dose-dependent reductions in acetylcholinesterase activity and muscarinic receptor binding in the cortex. During the preweanling period, there were no differences among the groups in most reflex measures, eye opening or incisor eruption. Postweanling behavioral assessment revealed small deficits in tests of spatial memory in both the T-maze and the radial arm maze. There were no differences in neuromuscular abilities or spontaneous activity measures. Thus, biochemical and behavioral deficits in cholinergic nervous system functioning occurred in the absence of severe signs of toxicity and in the absence of generalized nonspecific behavioral disturbances.

Acetylcholinesterase↗
PubMedDate not supplied

Formamidine pesticides and alpha 2-adrenoceptors: studies with amitraz and chlordimeform in rats and development of a radioreceptor binding assay.

The interaction of the formamidine pesticides chlordimeform (CDM) and amitraz (AMZ) with rat brain alpha2-adrenoceptors was investigated. Both compounds inhibited the binding of 3H-clonidine and 3H-yohimbine in vitro with IC50 values of 62-68 microM (CDM) and 95-110 nM (AMZ). In vivo administration of AMZ and CDM caused a dose-dependent inhibition of 3H-clonidine binding in rat forebrain. The inhibition was short-lasting (24 hr) following CDM administration, while after AMZ recovery of 3H-clonidine binding occurred only after 72 hr. Good correlations were found between inhibition of brain 3H-clonidine binding by the formamidines and "plasma equivalents" of these compounds and/or their biologically active metabolites, as measured by a new radioreceptor assay. These results suggest that 1) formamidines can interact in vivo with brain alpha 2-adrenoceptors when administered at doses previously shown to cause toxic effects on the central nervous system: and 2) this effect is reversible, both in vivo and in vitro, and appears to be linked to the presence of the formamidines and/or their active metabolites at the receptor sites.

Amidines↗
PubMedDate not supplied

Unidirectional cross-tolerance between the carbamate insecticide propoxur and the organophosphate disulfoton in mice.

Previous studies have shown that subchronic treatment of mice with the organophosphate insecticide, disulfoton, or the carbamate insecticide, propoxur, leads to the development of tolerance to their toxicity. Tolerance to disulfoton was due to a decrease in the number of muscarinic cholinergic receptors, while tolerance to propoxur appeared to be due to an induction of hepatic microsomal enzymes. In the present study we investigated if cross-tolerance between disulfoton and propoxur would occur. Cross-tolerance was evaluated by measuring acute toxicities, cholinesterase and carboxylesterase inhibition and hypothermic and antinociceptive effects. Mice tolerant to propoxur were cross-tolerant to the hypothermic and anticholinesterase effects of disulfoton. Similarly, when mice were pretreated with the microsomal enzyme inducer, phenobarbital, the toxicity of disulfoton was decreased. Mice made tolerant to disulfoton were cross-tolerant to the organophosphate chlorpyrifos, but were more sensitive than controls to the toxicity of propoxur. The acute toxicity of the organophosphate malathion was also increased in disulfoton-tolerant mice. Propoxur is metabolized by mixed function oxidases and possibly by a carboxylesterase. While hepatic microsomal enzymes appeared to be unchanged in disulfoton-tolerant mice, brain and liver carboxylesterase activities were significantly inhibited. Pretreatment of mice with the specific carboxylesterase inhibitor triorthotolylphosphate is known to greatly potentiate the toxicity of malathion and also potentiated, to a lesser extent, the toxicity of propoxur.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Kinetic analyses of the microsomal biotransformation of the phosphorothioate insecticides chlorpyrifos and parathion.

Chlorpyrifos [0,0-diethyl-0-(3,5,6-trichloro-2-pyridyl) phosphorothioate] was metabolized to chlorpyrifos oxon [0,0-diethyl-0-(3,5,6-trichloro-2-pyridyl) phosphate] and to 3,5,6-trichloro-2-pyridinol by mouse hepatic microsomes. Formation of both chlorpyrifos oxon and 3,5,6-trichloro-2-pyridinol required NADPH, and was inhibited by carbon monoxide. Kinetic analyses using direct linear plots determined the appKm's for formation of chlorpyrifos oxon and 3,5,6-trichloro-2-pyridinol to be 20.9 +/- 3.3 microM and 16.1 +/- 3.4 microM respectively, while the appVmax's for the same reactions were 3.9 +/- 0.2 nmols/100 mg liver/min and 8.1 +/- 0.3 nmols/100 mg liver/min respectively. Incubation of parathion [0,0-diethyl-0-(4-nitrophenyl) phosphorothioate] with mouse hepatic microsomes produced paraoxon [0,0-diethyl-0-(4-nitrophenyl) phosphate] and p-nitrophenol. The appKm's for the formation of paraoxon and p-nitrophenol were 29.6 +/- 4.2 microM and 26.5 +/- 3.8 microM respectively, with appVmax's of 5.8 +/- 0.6 nmols/100 mg liver/min and 6.7 +/- 0.5 nmols/100 mg liver/min, respectively. Incubation of both parathion and chlorpyrifos at various concentrations with mouse hepatic microsomes resulted in inhibition of production of paraoxon, p-nitrophenol, chlorpyrifos oxon, and 3,5,6-trichloro-2-pyridinol, which was characteristic of mixed type inhibition. This complex kinetic behavior could arise as a result of competitive interactions of parathion and chlorpyrifos with multiple forms of microsomal cytochrome P-450.

Animals↗
PubMedDate not supplied

Induction of anticholinesterase tolerance in rats with doses of disulfoton that produce no cholinergic signs.

The induction of anticholinesterase tolerance has, in the past, been achieved by using multiple doses of organophosphorus ester insecticides that initially caused cholinergic signs. The purpose of this study was to ascertain whether anticholinesterase tolerance could be induced with doses of an anticholinesterase that produced no overt cholinergic signs. Rats were fed diets containing 0, 7.5, or 20 ppm disulfoton. Animals fed at the 7.5 ppm level were without cholinergic signs throughout the period of feeding. Rats from this group were significantly more resistant to the lethal effect of carbachol than rats given the control diet after 58 and 62 d on the diet. Animals fed 20 ppm disulfoton in the diet initially showed signs that gradually disappeared with time on the diet. Rats fed at this level were more resistant to the lethal effect of carbachol than controls on all challenge dates (30, 45, 58, and 62 d on the diets) and more resistant than animals fed 7.5 ppm only on d 38 and 45. Thus the organophosphorus ester insecticide disulfoton, fed to rats in a dietary concentration that depressed acetylcholinesterase but was insufficient to cause cholinergic signs, induced tolerance to the lethal effects of carbachol. The length of time on an experimental diet before resistance to carbachol could be demonstrated was greater for the experimental group given 7.5 ppm disulfoton than the group given 20 ppm disulfoton in the diet.

Animals↗
PubMedDate not supplied

Interaction of choline with nicotinic and muscarinic cholinergic receptors in the rat brain in vitro.

The ability of choline to interact with nicotinic receptors was investigated by measuring its ability to inhibit the specific binding of [3H]-nicotine in rat brain. Choline, with an IC50 of 241 mumol/l, was three times more potent than its analogue deanol and almost 1000-fold less potent than acetylcholine. Choline also inhibited the binding of the antagonist [3H]-quinuclidinyl benzilate (IC50 = 2.5 mmol/l) and of the agonist [3H]-oxotremorine-M (IC50 = 165 mumol/l) to muscarinic cholinergic receptors. These results indicate that choline is able to interact directly, in vitro with brain cholinergic receptors of both the nicotinic and muscarinic type.

Acetylcholinesterase↗
PubMedDate not supplied

Antinociceptive effect of diisopropylphosphofluoridate: development of tolerance and lack of cross-tolerance to morphine.

The irreversible cholinesterase inhibitor diisopropylphosphofluoridate (DFP) causes a naloxone-sensitive antinociceptive effect in laboratory animals. Chronic treatment of male mice with DFP (2 mg/kg/day for fourteen days) rendered the animals tolerant to its antinociceptive effect. Animals tolerant to DFP were cross-tolerant to the antinociception induced by the cholinergic agonists oxotremorine and nicotine, but no cross-tolerance with morphine was observed. Similarly, mice made tolerant to morphine were not cross-tolerant to DFP, nor were they cross-tolerant to oxotremorine and nicotine. Binding of muscarinic and nicotinic cholinergic ligands was significantly decreased in the brain of DFP-tolerant mice, due to a reduction in receptor density. No change was observed in the binding of [3H]-dihydromorphine to opiate receptors. None of these three binding sites was altered in mice tolerant to morphine. Although there is evidence of an involvement of endogenous opioids in the antinociceptive action of DFP, the lack of cross-tolerance between DFP and morphine suggests the existence of a more complex interaction between DFP and the cholinergic and opiate systems.

Analgesics↗