To establish the dose dependency of phospholipase A2 (PLA2) inhibition by the organophosphorus compound (OPC) paraoxon (POX), human platelet membranes were incubated after Ca2+ removal (to inactivate the PLA2) with 0.3, 1 and 3 microg ml(-1) POX for 5, 30 and 60 min each. The PLA2 activity (pmol mg[-1] protein min[-1]) was measured after subsequent enzyme reactivation. The PLA2 activity in native platelets was considered to be 100%; all other measured values are expressed as a percentage thereof. Data were analysed with the Mann-Whitney Wilcoxon rank order test and ANOVA. Statistical significance was assumed for P < or = 0.01. Paraoxon inhibited in a dose-dependent manner the PLA2 activity. Different incubation times of the inactive PLA2 with POX did not have any additional effect on the activity reduction after activation. At the tested POX concentrations the PLA2 activity was 42 +/- 5.4%, 29 +/- 3.4% and 15 +/- 6.6%, respectively. The corresponding butyrylcholine esterase (BChE) activities were <<1% of the baseline activity. Phospholipase A2 is less sensitive to POX inhibition than BChE and, at clinically achievable POX concentrations, shows a clear dose dependency. Further work is needed to elucidate the exact mechanism and time dependency of the phenomenon.

Blood Platelets↗

PubMedDate not supplied

Control of blood pressure, heart rate and haematocrit during high-dose intravenous paraoxon exposure in mini pigs.

A therapeutic regimen was established to keep blood pressure, heart rate and haematocrit within the normal range during high-dose paraoxon (PX) exposure (ca. 150 x LD50) in mini pigs in order to achieve survival. Previous experiments showed that mini pigs exposed to high-dose PX died shortly after PX infusion due to hypertension, tachycardia and increased haematocrit if no antihypertensive and fluid therapy was initiated. Therefore, antihypertensive and fluid therapy with magnesium (MgSO4) and Ringer's solution was established to keep the blood pressure, heart rate and haematocrit within a pre-established normal range. Anaesthesized mini pigs received intravenously PX (54 mg kg(-1) body wt.) dissolved in alcohol. The control group received alcohol in corresponding amounts. When the blood pressure and heart rate increased, MgSO4 was given intravenously until measured values reached the normal range. When the haematocrit increased, fluids were given intravenously until the haematocrit reached the normal range. The measured values in the PX group were compared with the measured values of the control group using the 'rank order test'. As intended, no statistically significant differences between blood pressure, heart rate or haematocrit were found after therapy, but the PX group required statistically significantly more MgSO4 and fluids than the control group to keep the blood pressure, heart rate and haematocrit within the normal range. We assume that the increased need of antihypertensive therapy is due to a phaeochromocytoma-like pattern caused by an excessive release of catecholamines from the adrenal medulla, which is under sympathotonic control and activated by acetylcholine. Paraoxon is known to cause endogenous acetylcholine poisoning. The high fluid requirements in the PX group are most probably caused by extravasation of fluids due to the damage inflicted on biological membranes by organophosphorus compounds. An activation of secretory glands probably also contributes to the increase in haematocrit through consumption of fluids. In conclusion, the survival of mini pigs exposed to high-dose PX can be achieved by tight control of blood pressure, heart rate and haematocrit using MgSO4 and fluids.

Animals↗

PubMedDate not supplied

L-lactate reduces in vitro the inhibition of butyrylcholinesterase (BChE) by paraoxon (E 600).

Intoxication with the organophosphorus compound paraoxon (POX), an inhibitor of serine hydrolases, is frequent. Oximes are the only enzyme reactivators clinically available. Serendipitous observation led us to the hypothesis that lactate might attenuate some of the POX effects. In vitro effects of lactate on the inhibition of butyrylcholinesterase (BChE) by POX were assessed in plasma of 12 healthy human volunteers. The determinations were repeated using different lactate and different POX concentrations. The BChE activity determinations were performed in the following settings: (i) baseline untreated plasma (BL); (ii) after addition of POX to plasma (pl+POX); (iii) after POX and plasma were incubated and then lactate was added (pl+POX/lact); (iv) after addition of lactate to plasma (pl+lact); (v) after lactate and plasma were incubated and then POX was added (pl+lact/POX); (vi) after lactate and POX were incubated and then added to plasma (lact+POX/pl). In the micro- and millimolar ranges, lactate is able to abolish in vitro the inhibition of BChE by POX in human plasma when added to plasma prior to POX or when incubated with POX prior to addition to plasma. Lactate added to plasma after POX has no protective effect. In a second set of experiments, the effect of lactate on BChE activity was determined. At high millimolar concentrations, lactate itself inhibits BChE to an extent comparable to POX. Lactate is a mixed inhibitor of BChE, being able to interfere with the enzyme-substrate complex (inhibition constant for the enzyme-inhibitor-substrate complex K'I(EIS) = 81 mM) and the enzyme (inhibition constant for the enzyme-inhibitor complex K(I) (EI) = 26 mM).

Butyrylcholinesterase↗

PubMedDate not supplied

L-lactate protects in vitro acetylcholinesterase (AChE) from inhibition by paraoxon (E 600).

Intoxication with the organophosphorus compound paraoxon (POX), an inhibitor of serine hydrolases, is frequent. Oximes are the only enzyme reactivators clinically available. Recent work has shown that lactate is able to reduce in vitro the POX effects on butyrylcholinesterase (BChE). Most of the acute clinical symptoms, however, are caused by inhibition of acetylcholinesterase (AChE). Effects of lactate on the inhibition of AChE by POX were assessed in vitro in plasma of 12 (six male, six female) healthy human volunteers. The determinations were repeated using different lactate and different POX concentrations. The AChE activity determinations were performed in the following settings: (BL) baseline (untreated plasma); (a) after addition of POX to plasma (pl + POX); (b) after POX and plasma were incubated and then lactate was added (pl + POX/lact); (c) after addition of lactate to plasma (pl + lact); (d) after lactate and plasma were incubated and then POX was added (pl + lact/POX); (e) after lactate and POX were incubated and then added to plasma (lact + POX/pl). In the micro- and millimolar ranges, lactate is able to protect in vitro AChE from inhibition by POX when added to human plasma prior to POX or when incubated with POX prior to addition to plasma. Lactate added to plasma after POX has no protective effect. In a second set of experiments, the effect of lactate on AChE activity was determined. At high millimolar concentrations, lactate itself inhibits AChE non-competitively (mixed inhibition) to an extent comparable to POX (inhibition constant K(I) = 254 mM).

Acetylcholinesterase↗

PubMedDate not supplied

Pralidoxime and l-lactate effects in vitro on the inhibition of acetylcholinesterase by paraoxon: pralidoxime does not confer superior protection.

Intoxication with the organophosphorus compound paraoxon (POX), an inhibitor of serine hydrolases, is frequent. Although oximes are the only enzyme reactivators presently available, clinical experience with their use was rather disappointing. Recent work has shown that under certain conditions l-lactate is also able to reduce in vitro the POX inhibition of butyrylcholine- and acetylcholineesterase (BChE and AChE). To assess the practical relevance, if any, of these findings, the protective effects of pralidoxime (PRX) and those of lactate had to be compared in the same in vitro model. Effects of PRX on the inhibition of AChE by POX were assessed in vitro in plasma of 12 (six male and six female) healthy human volunteers. The determinations were repeated using different oxime and different POX concentrations. The AChE activity determinations were performed using the following sampler: sample BL-baseline (or untreated plasma); sample a-after addition of POX to plasma (pl + POX); sample b-after POX and plasma were incubated and then oxime was added (pl + POX/PRX); sample c-after addition of oxime to plasma (pl + PRX); sample d-after oxime and plasma were incubated and then POX was added (pl + PRX/POX); sample e-after oxime and POX were incubated and then added to plasma (PRX + POX/pl). Results were corrected for spurious enzyme 'pseudo-activity' due to interaction between PRX and substrate (acetylthiocholine) in the absence of enzyme. In the micro- and millimolar ranges, PRX is able to protect in vitro AChE from inhibition by POX when added to human plasma prior to POX or when incubated with POX prior to addition to plasma. Adding PRX to plasma after POX has no protective effect. The PRX results were compared statistically with historical lactate data (obtained under identical conditions) using the Wilcoxon matched pairs test, with significance assumed for p = 0.01. No difference between PRX and lactate's protective effect on the AChE inhibition by POX was found in the in vitro model used. We therefore conclude that in vivo testing of lactate as a POX protective agent is warranted.

Acetylcholinesterase↗

PubMedDate not supplied

High-dose intravenous paraoxon exposure does not cause organophosphate-induced delayed neuropathy (OPIDN) in mini pigs.

Organophosphorus compounds are inhibitors of serine hydrolases. Some of these compounds produce, in addition to their high acute toxicity, a more persistent effect: organophosphate-induced delayed neuropathy (OPIDN). The putative molecular entity whose inhibition is thought to be responsible for OPIDN is the neuropathy target esterase (NTE). Although in vitro NTE is resistant to paraoxon (PX), occasional case reports have associated PX with OPIDN. To assess clinically whether or not high-dose i.v. PX causes OPIDN in mini pigs, 14 mini pigs were anaesthesized, intubated and mechanically ventilated. In a first set of experiments eight pigs received 1 mg PX kg(-1) body weight (BW) dissolved in alcohol. Two control animals received alcohol in a corresponding amount. After infusion of PX, survival of the animals during the acute phase of intoxication was achieved by intensive-care support, using appropriate drugs and fluids according to a pre-established protocol. The mini pigs were extubated 1036 +/- 363 min later (mean +/- SD). The pigs were observed prior to PX application and for 6 weeks thereafter for any abnormalities and/or signs of OPIDN, such as leg weakness, ataxia and paralysis. Observations were graded on a scale for three categories (position, motor deficiency, reaction), with a maximal cumulative score of 9. In a second set of experiments (four additional pigs) larger PX doses were used (3, 9, 27 and 81 mg kg(-1) BW). After recovering from general anaesthesia/surgery, within 2 weeks all animals reached the initial score on the scale. It can be concluded that high-dose i.v. PX exposure does not induce OPIDN in mini pigs during the 6-week observation period.

Animals↗

PubMedDate not supplied

Kinetics of intravenous L-lactic acid in anaesthetized minipigs under normoxic/normocapnic/normohydrogenaemic conditions.

A mild and transitory increase in L-lactic acid (LAC) levels can be achieved by LAC infusion under normoxic/normocapnic/normohydrogenaemic conditions. This increase is probably sufficient to confer some protection to cholinesterases from inhibition by organophosphates.

Animals↗

PubMedDate not supplied

Idiopathic chronic hiccup: combination therapy with cisapride, omeprazole, and baclofen.

Idiopathic chronic hiccup (ICH) is defined as recurring hiccup attacks that last for longer than an arbitrary time limit (eg, 1 month) and for which no organic cause can be found. In patients with ICH, therapy is largely empiric. For practical purposes, idiopathic hiccup can be assumed to have its origin either in the viscera (gastrointestinal tract) or in the central nervous system. Cisapride and omeprazole--through reduction of gastric acid production and facilitation of gastric emptying, respectively--are thought to reduce an assumed afferent input from the periphery to a putative supraspinal hiccup center. Baclofen is thought to reduce excitability and depress reflex hiccup activity. Fifteen male patients (mean [+/- SD] age, 68.2 +/- 11.6 years) who had recurring hiccup attacks for a mean duration of 100.8 +/- 134.1 months (range, 12 to 564 months) were treated for ICH with a combination of cisapride, omeprazole, and baclofen (COB). Therapy led to a total disappearance of hiccup in 40% (6 of 15) of the treated patients. An additional 20% (3 of 15) of patients experienced substantial relief. A Mann-Whitney rank order test showed a highly significant reduction in the severity of the hiccup attacks as reflected in the subjective assessment scale scores taken before therapy (8.6 +/- 1.3) compared with those taken after 20 weeks of therapy (4.1 +/- 3.8). Thus we concluded that COB is an effective empiric therapy in at least some patients with ICH.

Adult↗

PubMedDate not supplied

Sonomatic confirmation of tracheal intubation using the SCOTI.

This study compares the performance of two commercially available devices (Ambu TubeChek and SCOTI) in establishing endotracheal (ET) tube position (oesophageal vs. tracheal) in a mannequin and in miniature pigs. The Ambu TubeChek is a syringe-type, Oesophageal Detector Device (ODD) that fits to the endotracheal tube connector. Air is aspirated easily from the rigid trachea, but not from the collapsing esophagus. The Sonomatic Confirmation of Tracheal Intubation device (SCOTI) is a lightweight battery-powered, sonomatic device. It emits sound waves into the tube and analyzes the reflection. The SCOTI purports to enable a user-independent and carbon-dioxide-independent assessment of tube position following intubation. Intubation followed by tube position assessment with Ambu TubeChek (ODD) was significantly faster and easier with the ODD than with the SCOTI. The SCOTI cannot differentiate tracheal from oesophageal ET-tube position in mini-pigs. In situations in which capnometry is not available or the CO2 production and transport are compromised (CPR), we recommend the use of an Oesophageal Detector Device (ODD) rather than the SOCTI.

Animals↗