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  • 1
    ISSN: 1432-0738
    Keywords: Neuropathy ; Organophosphorus ; Trichlorphon ; Neurotoxic Esterase ; Screening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Progressive neuropathy developed in a man during 2–8 weeks after acute poisoning by a pesticide said to contain trichlorphon. The neuropathy was typical of that caused by organophosphorus esters in the delay and in the maintenance of normal conduction velocity in surviving nerve fibres. A sample alleged to be typical of the ingested material was not more active against hen brain neurotoxic esterase (NTE) than was pure trichlorphon. Delayed neuropathy has never been produced in hens by a single dose of trichlorphon. This incident and studies of human brain in vitro suggest that the ratio neurotoxicity/lethality for trichlorphon is higher in man than in the hen. Suggestion is made of laboratory tests to improve neurotoxicity screening.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Archives of toxicology 34 (1975), S. 259-288 
    ISSN: 1432-0738
    Keywords: Organophosphates ; Neurotoxicity ; Mechanism ; Structure/Activity ; Organophosphate ; Neurotoxizität ; Wirkungsmechanismus ; Struktur-Aktivitätsbeziehungen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Wirkungsmechanismus Die Beweisführung nimmt an, daß die Phosphorylierung des aktiven Zentrums eines spezifischen Enzyms, “neurotoxische Esterase” genannt, das initiale biochemische Ereignis der zur verzögerten Neurotoxizität führenden Reaktionsfolge ist. Darauf folgt die Spaltung einer Bindung (hydrolytisch?) die einen monosubstituierten Phosphorsäurerest am Protein hinterläßt. — Der Mechanismus, auf dem die Schutzwirkung einiger Phosphonsäureester gegenüber neurotoxischen Substanzen beruht, wird erläutert. Screening-Methode Die Bestimmung der Wirkung auf die Aktivität der “neurotoxischen Esterase” im Hühnergehirn (in vitro und in vivo) stellt eine schnelle biochemische Probe zur Ergänzung des 3wöchigen klinischen Tests dar. Der Test erlaubt die Abschätzung von Sicherheitsgrenzen für Substanzen, die negative Ergebnisse im klinischen Test erbringen und häufig als Pestizide, Weichmacher usw. verwendet werden. Vereinfachte Bestimmungsmethoden wurden entwickelt. Struktur-Wirkungs-Eeziehungen Für viele Verbindungen liegen Daten über die biochemische und neurotoxische Wirkung vor. Diese dienen als Basis für Vorhersagen von Struktur-Wirkungs-Beziehungen. Die seit 1930 veröffentlichten Daten zur Neurotoxizität werden unter diesem Gesichtspunkt behandelt.
    Notes: Abstract Mechanism of Action Evidence is reviewed that the initial biochemical event leading to delayed neurotoxicity is phosphorylation of the active site of a specific enzyme called Neurotoxic Esterase. This is followed by a bondcleavage (? hydrolytic) leading to formation of a mono-substituted phosphoric acid residue on the protein. The mechanism by which some phosphinates protect hens against neurotoxic compounds is explained. Screening Assay Assay of effects of compounds on Neurotoxic Esterase activity of hen brain in vitro and in vivo provides a quick biochemical screen to supplement the 3-week clinical test. This test provides an estimate of safety margin for compounds which give negative results in the clinical test and are currently used as pesticides, plasticisers, etc. Simplified assay procedures are being developed. Structure/Activity Studies Data is now available for the biochemical and neurotoxic activity of many compounds. This provides a basis for structure/activity predictions; neurotoxicity data published since 1930 has been assessed in this light.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0738
    Keywords: Methamidophos ; Pesticide ; Phosphoramidates ; Organophosphorus ; Neuropathy target esterase (NTE) ; Delayed neuropathy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The interaction with neural neuropathy target esterase (NTE) and acetylcholinesterase (AChE) in vivo of methamidophos (O,S-dimethyl phosphorothioamidate), its resolved stereoisomers and five higher O-alkyl homologues has been examined along with the ability of these compounds to cause organophosphorus-induced delayed polyneuropathy (OPIDP) in adult hens. For the lower homologues AChE was more sensitive than NTE and it was impossible to achieve high inhibition of NTE in vivo without both prophylaxis and therapy against acute anticholinesterase effects; for then-hexyl homologue high inhibition of NTE could be achieved without obvious anticholinesterase effects and spontaneous reactivation of inhibited AChE was seen as in vitro. The maximum tolerated dose ofl(−) methamidophos or of the ethyl oriso-propyl homologues did not inhibit NTE more than 60%, and surviving birds did not develop OPIDP. Then-propyl,n-butyl andn-hexyl compounds caused typical OPIDP at doses causing a peak of 70–95% inhibition of NTE in brain, spinal cord and sciatic nerve soon after dosing. Racemic methamidophos caused unusually mild OPIDP associated with very high inhibition of NTE at doses estimated to be 〉8 times the unprotected LD50 and thed-(+) isomer caused OPIDP at about 5−7× LD50. Clinical effects correlated with histopathology in 19 out of 20 examined birds. In contrast to results of many previous studies with organophosphates and phosphonates, all these cases of OPIDP were associated with formation of inhibited NTE which could be reactivated ex vivo by treatment of autopsy tissue with KF solution. It is not clear whether “aging” of inhibited NTE had occurred but with less associated stabilisation of the enzyme-phosphorus bond or whether, even without aging, the unusual N-unsubstituted phosphoramidate caused sufficient disturbance in or near the NTE target to initiate the same degenerative process as that caused typically by generation of “aged” organophosphorylated NTE.
    Type of Medium: Electronic Resource
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