Sugar-oximes, new potential antidotes against organophosphorus poisoning

In attempt to improve distribution and transport qualities of antidotes against organophosphorus poisoning, a new series of pyridine aldoximes linked to glucose moiety were synthesized and studied both in vivo and in vitro. Preliminary results describing the biological activity of the new compounds are presented and discussed in this report.

The ganglionic blocking properties of the cholinesterase reactivator, HS-6

Following intravenous administration of the cholinesterase reactivator HS-6 (30 mg/kg), blood pressure fell (up to 50 mmHg) and maximal blood levels of HS-6 reached 242 microgram/ml. HS-6 attenuated the pressor response resulting from carotid occlusion and the depressor effect of vagal stimulation. Doses of HS-6 below those used to protect against soman in different animal species (10--30 mumol/kg) progressively blocked the ganglion-stimulating effects of nicotine and dimethylphenylpiperazinium but not the pressor effect following adrenaline, a pattern similar to that produced by hexamethonium but only 1/84 as potent. HS-6, like hexamethonium and mecamylamine, progressively blocked the contraction of the nictitating membrane of the cat resulting from preganglionic stimulation. The results indicate that HS-6 possesses ganglion-blocking properties at doses likely to be used in the protection against soman poisoning. The ganglion-blocking properties of the drug may be a factor in the beneficial effects of HS-6.

[Central action of a new cholinesterase reactivator, diethyxime]

In anesthetized cats, whose peripheral muscarinic-cholinorecptors are blocked by m-cholinolytics (benzilyl choline) failing to penetrate into the brain, the cholinesterases reactivator diethyxime debars the centrally caused fall of the arterial pressure produced by armine, an inhibitor of cholinesterases readily gaining access into the brain. Diethyxime is also capable of abolishing the depression of the phrenic nerve action potentials produced by armine. Dipyroxime-a quaternary diethyxime analogue and also a quaternary cholinesterase reactivator fails to produce such an effect.

[Muscarin-sensitive cholinoreactive systems in the respiratory center]

Muscarinic cholinergic drugs (arecoline, oxotremorine) which can easily overcome the blood-brain barrier inhibit the action potentials of the phrenic nerve in anesthetized or decerebrate curarized cats after a selective blockade of peripheral muscarinic cholinoreceptors with quaternary anticholinergic drugs (oxyphenonium, benzilycholine). These inhibitory effects are abolished by drugs blocking the central muscarinic cholinoreceptors (atropine, scopolamine, benactyzine). This suggests the existence of muscarinic cholinoreceptive neurons in the respiratory center of the cerebral ponto-bulbar region, the said neurons inhibiting the activity of the inspiratory motonerons.

Cholinesterase reactivators - contribution to the study of their metabolic effects

Cholinesterase reactivators - trimedoxim, methoxim and obidoxim - injected in the dose of 20 mg/kg s.c., increase muscle glycogen concentration in normal, but not in adrenalectomized rats. This effect may be in connection with simoultaneously found rise of serum corticosteron level. Trimedoxim decreases adrenaline, methoxim and obidoxim noradrenaline concentration in adrenals.

Some pharmacological correlations of hypothermia induced by anticholinesterasics

The investigations have been performed on Wistar rats intoxicated with paraoxon in toxic sublethal doses. There have been measured the variations of rectal temperature at various time periods following the anticholinesterase agent. The authors established the pharmacodynamic correlations of paraoxon-induced hypothermia with cholinesterase reactivators (toxogonin, isonitrosine), anticholinergic substances (atropine, butylscopolamine), carbamic anticholinesterase (eserine, neoeserine) and chlorpromazine. The efficiency of atropine and cholinesterase reactivators in antagonization of hypothermia induced by organophosphorics on the one hand, and only of atropine against hypothermia induced by carbamates on the other hand allow the hypothesis of a central cholinergic mechanism, predominantly muscarinic, involved in hypothermia induced by anticholinesterasics and of a direct correlation of this mechanism with phosphorylation or carbamylation processes of cerebral cholinesterases.

[Reactivation by 1-hydroxyimino-4-methyl-2-pentamone of plasma cholinesterases in the dog inhibited by different orgenophosphates]

The hydroxyimino-1 methyl-4 pentanone-2 was selected among several oximes because of its highly successful restoring action on dog plasmatic cholinesterases inhibited by DFP (diisopropyl fluorophosphate). During the in vitro study, this storing action was tested on 10 organophosphates. Results are compared to those obtained when contrathion is used.

[Experimental data on a new cholinesterase reactivator from the group of thiohydroximic esters]

Experimental data on the effectiveness of p-brombenzothiohydroximic S-diethylaminoethylate (diethyxime) -a new cholinesterase reactivator - are presented. The diethyximetoxicity with its single and multiple administration to animals was studied. The drug is shown to display a marked antidotal action when used in a dosage range of 490-10 mg/kg. Diethyxime is shown capable of restoring the activity of cholinesterase inhibited by dimethyldichlorovenylphosphate, of preventing the neuro-muscular block of the impulses conduction and of normalizing the function of the cardiovascular system. The drug is less toxic than is presently employed reactivator diproxime and it does not produce any side-effects on a number of organs and systems of the organism with its multiple administration to worm-blooded animals.

[Effect of cholinesterase inhibitors and reactivators on the blocking action of dicarboxylic acid amino esters on neuromuscular conduction]

Inhibition of active cholinesterases in cats with armine or the GT-165 compound (0,0-diethyl-S-/beta-arylmethylamino) ethyl/thiophosphate methylsulphomethylate) potentiases ten- and hundred-fold the blocking action of subecholine and its derivatives on the neuro-muscular condution. The cholinesterase reactivator dipyroxime (2-5 mg/kg) quickly lifts the conduction block, provoked by muscle relaxants of the subecholine type under the cholinesterase inhibition. The subecholine analogue with a single propyl radical at each atom of nitrogen does not display any pressor action and, upon inhibition of cholinesterases, it blocks the neuro-muscular conduction when used in a dose of 0.1-0.2 gamma/kg. The maximal potentiation of the blocking action exerted by subecholine and its analogues is achieved in inhibiting not only pseudocholinesterase but acetylcholinesterase as well.

Cholinesterase reactivation: in vitro studies

In vitro studies confirm the clinical impression that P–2–AM does not reverse the cholinesterase inhibition caused by organophosphorus insecticides.