Chronic intraperitoneal endotoxin treatment in rats induces resistance to d-tubocurarine, but does not produce up-regulation of acetylcholine receptors.

BACKGROUND: Chronic systemic inflammation resulting from intraperitoneal Eschevichia coli endotoxin administration or Corynebacterium injections induces tolerance to non-depolarizing neuromuscular blockers in rodents. Although this has been explained as up-regulation of muscle acetylcholine receptors (AChR), the numbers of involved receptors have not been documented. The aim of this study was to determine the effects of chronic endotoxin administration on rat muscle AChR. METHODS: One day after one, seven, or 14 daily intraperitoneal doses of lipopolysaccharide endotoxin (0 or 0.5 mg kg(-1)), we studied in vivo dose-response relationships for d-tubocurarine (d-Tc) and AChR binding using [125I]alpha-bungarotoxin as a ligand. RESULTS: One day after seven and 14 daily intraperitoneal doses of endotoxin, the effective dose of d-Tc required to suppress the twitch response to 50% of the control (ED50) was significantly increased compared with that of time-matched control rats (146.5 +/- 38.2 vs. 76.1 +/- 9.0 microg kg(-1) for seven doses; 116.4 +/- 51.3 vs. 74.4 +/- 9.6 micro g kg-1 for 14 doses, P < 0.05). However, this was not associated with an increase in the number of AChR in the anterior tibial muscle or diaphragm. CONCLUSIONS: Mechanisms other than AChR up-regulation might be responsible for the increased d-Tc requirement during chronic intraperitoneal endotoxin administration.

Sepsis attenuates the intensity of the neuromuscular blocking effect of d-tubocurarine and the antagonistic actions of neostigmine and edrophonium accompanying depression of muscle contractility of the diaphragm.

BACKGROUND: Prolonged effects of non-depolarizing muscle relaxants in septic patients have been reported, although the influence of sepsis on neuromuscular transmission has not yet been clarified satisfactorily. These studies were intended to elucidate the influence of sepsis on neuromuscular transmission and on the action of drugs being utilized for regulation of muscle tone (a neuromuscular blocker and anti-cholinesterase (anti-ChE) drugs). METHODS: The effect of d-tubocurarine (dTc) on neuromuscular transmission and the antagonistic action of anti-ChE drugs (neostigmine and edrophonium) on dTc-induced twitch depression were estimated using sham control and septic rat nerve-hemidiaphragm preparations in vitro. Isometric twitch tension elicited by indirect (phrenic nerve) or direct (muscle) stimulation at 0.1 Hz was evaluated. RESULTS: Sepsis induced by panperitonitis attenuated the twitch tension elicited by indirect or direct stimulation (P < 0.01) without obvious morphological inflammatory damage to the diaphragm. dTc dose-dependently decreased twitch tension elicited by indirect stimulation (P < 0.01) less intensely in the septic group than in the sham group (P < 0.01). The antagonistic actions of the anti-ChE drugs on dTc (1 microM)-induced twitch depression were less intense in the septic group (P < 0.01 or 0.05). CONCLUSION: These results demonstrate that sepsis in the acute phase attenuates the effects of a neuromuscular blocker and anti-ChE drugs and depresses muscle contractility simultaneously.

Study of in vitro and in vitro effects of isradipine in skeletal muscles and interaction with some drugs.

The effects of the calcium channel blocker isradipine were studied in the indirectly and directly stimulated mouse diaphragm and in the anesthetized rat to determine its potency, reversibility and interaction with a number of drugs. Initially, it potentiated both indirect and direct twitches followed by a reduction. With tetanic contractions, no potentiation was obtained, only a reduction, which was complete or near complete at the highest concentration tested (10(-4) M). In combination, isradipine reduced the IC50 and IC90 values for the antibiotics gentamicin, polymyxin B and clindamycin, d-rubocurarine and magnesium ions. Depression of contraction caused by isradipine or in combination could be reversed to varying degrees by washout, elevated calcium ions, neostigmine or 4-aminopyridine. Spontaneous recovery from the effects of isradipine alone or in combination was slow and usually incomplete. For in vivo experiments, severe cardiovascular depressant effects of isradipine limited its exposure to lower concentrations and for shorter periods. Under these conditions, it had no effect on heart rate. However, both systolic and diastolic blood pressure were significantly reduced, while pulse pressure was increased. After an initial potentiation muscle contraction was maximally reduced to 55% of control. This study indicates that acute administration of isradipine may aggravate neuromuscular effects of antibiotics, muscle relaxants or hypermagnesemia, although it is unlikely that spontaneous recovery or reversibility of muscular activity by suitable reversal agents will be affected. However, prolonged use of the drug may be more difficult to reverse.

The prejunctional inhibitory effect of suramin on neuromuscular transmission in vitro.

The P2 purinoceptor antagonist suramin reverses skeletal muscle paralysis evoked by non-depolarizing neuromuscular blocking agents in vitro and in vivo. To further study the action of suramin on neuromuscular transmission, (miniature) endplate potentials ((m.)e.p.ps), motor nerve terminal currents and the release of radiolabeled acetylcholine was measured in isolated nerve-muscle preparations. In preparations paralysed by low Ca2+/high Mg2+ conditions, suramin (10 microM-1 mM) induced a concentration-dependent decrease in quantal content of the e.p.ps without affecting m.e.p.ps. Suramin reversed neuromuscular block by d-tubocurarine in these preparations. In erabutoxin paralysed preparations, suramin (40 microM-1 mM) inhibited the motor nerve terminal currents related to Ca2+ influx concentration-dependently, but did not affect Na+ currents. Suramin-induced inhibition of Ca2+ currents was not antagonized by ATP gamma S. Suramin (300 microM) reduced [14C]acetylcholine outflow in non-paralysed rat phrenic nerve-hemidiaphragm preparations by 32%. As suramin did not chelate Ca2+, these results indicate that suramin inhibits neuromuscular transmission by blocking prejunctional Ca2+ channels, thereby decreasing acetylcholine release upon nerve stimulation.

Effect of nizatidine and ranitidine on the D-tubocurarine neuromuscular blockade in the toad rectus abdominis muscle.

The influence of varying concentrations of the H2-receptor antagonists nizatidine and ranitidine on the acetylcholine- and carbachol-induced contractures on the toad rectus abdominis muscle, as well as the possible interaction between the above H2-receptor antagonists and D-tubocurarine were studied. Nizatidine and ranitidine at a concentration of 3.2 x 10(-4) mol l-1 augmented, and at 3.2 x 10(-3) mol l-1 inhibited, the acetylcholine-induced contractures on the toad rectus abdominis muscle, while at concentrations from 3.2 x 10(-4) to 3.2 x 10(-3) mol l-1 they inhibited the carbachol-induced contractures, in a concentration-dependent manner. In addition, nizatidine and ranitidine at a concentration of 3.2 x 10(-4) mol l-1 reversed the D-tubocurarine blocking activity on the acetylcholine-induced contractures, but at a concentration of 3.2 x 10(-3) mol l-1 they augmented it. These findings provide evidence that the above H2-receptor antagonists produce either cholinesterase inhibition or neuromuscular blockade, depending on their concentration. Thus, the D-tubocurarine neuromuscular blocking activity is potentiated at high concentrations of nizatidine and ranitidine, while it is reversed at lower ones.

Interactions between suxamethonium and non-depolarizing neuromuscular blocking drugs.

In anaesthetized cats, we have confirmed that previously injected suxamethonium potentiates non-depolarizing neuromuscular blocking drugs whereas, when injected during the block, suxamethonium antagonizes the paralysis. We have attempted to explain these interactions by studying the effects of suxamethonium on extracellularly recorded nerve ending waveforms that correspond to the ionic currents in the mouse triangularis sterni isolated nerve-muscle preparation. The preparations were paralysed with mu-conotoxin (obtained from the cone snail), which is believed to act by selectively blocking sodium channels in muscle, and which therefore should not interfere with currents at the nerve endings. Suxamethonium, in concentrations of 0.5-300 mumol litre-1, produced a concentration-dependent increase in the amplitude of the waveform corresponding to the inward calcium current evoked by a nerve impulse. This effect did not occur in the presence of tubocurarine, suggesting that suxamethonium, which is a nicotinic agonist, may have been acting on a nicotinic receptor on the nerve endings that is coupled to the voltage-operated calcium channels. The inward calcium current is believed to be responsible for neurotransmitter (acetylcholine) release. It is concluded, therefore, that its enhancement by suxamethonium contributes to the ability of this drug to reverse non-depolarizing block. Suxamethonium also exerted complex effects on the waveform corresponding to the outward flowing calcium-activating potassium current at the nerve endings, but no effect was observed in this isolated nerve-muscle preparation that could obviously explain the ability of suxamethonium to potentiate subsequently injected non-depolarizing blocking drugs.

The influence of the H1 and H2 receptor antagonists, terfenadine and ranitidine on the hypotensive and gastric pH effects of the histamine releasing drugs, morphine and tubocurarine.

Morphine and tubocurarine may release histamine by direct mast cell degranulation which may result in systemic effects such as cutaneous flushing, local wheal and flare formation and hypotension. This randomised, double-blind study examined whether preoperative combined oral terfenadine (60 mg) and ranitidine (150 mg) attenuates the reduction in blood pressure and cutaneous flushing after the administration of tubocurarine and morphine in 60 patients undergoing elective gynaecological surgery. In addition, investigation was made of whether tubocurarine and morphine cause a significant decrease in gastric pH in comparison to the nonhistamine-releasing agents fentanyl and vecuronium. Patients were randomly assigned to one of three groups receiving either pre-operative terfenadine and ranitidine and intra-operative tubocurarine and morphine (group A); pre-operative placebo and intra-operative tubocurarine and morphine (group B); pre-operative placebo and intra-operative fentanyl and vecuronium (group C). Compared to group B, group A had less hypotension and tachycardia but no significant decrease in cutaneous flushing immediately following morphine and tubocurarine (p > 0.05). There were no significant differences in haemodynamic changes between the groups A and C. In those patients not pretreated with terfenadine and ranitidine (groups B and C), gastric pH decreased between 5 and 10 min following bolus administration of morphine and tubocurarine (group B), whereas patients receiving fentanyl and vecuronium (group C) had an increase in gastric pH. This suggests that histamine release following administration of morphine and tubocurarine is sufficient to increase gastric acidity.(ABSTRACT TRUNCATED AT 250 WORDS)

Atracurium after an anticholinesterase. Does prior reversal with edrophonium or neostigmine influence the response to atracurium?

This study documents the response to atracurium (75 micrograms.kg-1) administered 30 min after a pancuronium- or tubocurarine-induced neuromuscular block has been reversed with either neostigmine (50 micrograms.kg-1) or edrophonium (0.5 mg.kg-1). Twenty-one ASA 1 or 2 patients were studied, of whom 11 received neostigmine and 10 edrophonium. The degree of neuromuscular block was measured electromyographically from the first dorsal interosseous muscle of the hand using train-of-four stimulation of the ulnar nerve. When atracrium was administered, the single twitch response compared with control was 100% in all patients and the mean train-of-four ratios were 91% and 65% in the neostigmine and edrophonium groups respectively. After atracurium (75 micrograms.kg-1), minimum values for the single twitch response compared with control were 52% and 66% in the neostigmine and edrophonium groups respectively. Prior administration of atracurium appears to potentiate the neuromuscular blocking effects of atracurium administered 30 min later.

Prejunctional action of neostigmine on mouse neuromuscular preparations.

We have studied the effects of neostigmine on the mouse diaphragm and triangularis sterni isolated nerve-muscle preparations. Mechanical responses of the muscle, end-plate potentials and miniature end-plate potentials, and extracellularly recorded nerve ending currents were recorded. In the mouse diaphragm nerve-muscle preparations, neostigmine 1 mumol litre-1 continued to produce some antagonism of tubocurarine-induced block after cholinesterase had been inactivated completely by diisopropyl fluorophosphate 22 mumol litre-1. In the mouse triangularis sterni preparation, neostigmine 0.1-1 mumol litre-1 increased the quantal content of the end-plate potential in a concentration-dependent manner. This effect appeared to be sufficient to account for the cholinesterase-independent antagonistic action to tubocurarine under the conditions of the experiments. Neostigmine 1-100 mumol litre-1 depressed the amplitude of the K+ currents of the perineural waveforms in a concentration-dependent manner, and this may account for its ability to increase the quantal content of the end-plate potential. Although inhibition of acetyl-cholinesterase is the main mechanism of action of neostigmine, the drug also exerts an additional direct action on motor nerve endings to block the delayed rectifier K+ channels and enhance transmitter release. This effect occurred at clinically relevant concentrations of neostigmine. Physostigmine and pyridostigmine did not possess this additional action.

Neostigmine and edrophonium antagonism of moderate neuromuscular block induced by pancuronium or tubocurarine.

Edrophonium and neostigmine are anticholinesterase drugs used commonly to antagonize competitive neuromuscular block. Although it has a faster onset of action than neostigmine, edrophonium is unreliable when used to antagonize deep neuromuscular block. We have compared the antagonist characteristics of these two drugs when used to antagonize a moderate degree of pancuronium- or tubocurarine-induced neuromuscular block. Forty ASA I or II patients undergoing surgical procedures were allocated randomly to receive either pancuronium 70 micrograms kg-1 or tubocurarine 0.5 mg kg-1, and to receive either edrophonium 0.5 mg kg-1 or neostigmine 0.05 mg kg-1. Antagonism was attempted when the first response to train-of-four (TOF) stimulation recovered spontaneously to 25% of the control height. Neuromuscular function was monitored using the evoked integrated electromyogram of the first dorsal interosseous muscle of the hand. Adequate recovery was defined as the achievement of a TOF ratio of 0.70 or greater. Only seven of 20 patients who received edrophonium demonstrated adequate recovery 30 min after antagonism. Under the conditions described in this study, edrophonium 0.5 mg kg-1 was less effective as an antagonist than neostigmine 0.05 mg kg-1.

[A microelectrode study of the antagonism of d-tubocurarine induced neuromuscular blockade by edrophonium and neostigmine].

It has been reported clinically that edrophonium (EDR) has a more potent antagonistic effect on the fade of twitch tension and a less potent antagonistic effect on the depressed single twitch force induced by muscle relaxants than does neostigmine (NST). However, the details of the mechanism have not yet been clarified. In this experiment, to compare the antagonistic effect of EDR and NST on the neuromuscular blocking effect of dTc, the recovery from dTc induced neuromuscular blocking effect on both the postjunctional membrane and the motor nerve terminal with EDR or NST was studied using intracellular recording techniques in rat phrenic nerve-hemidiaphragm preparations. The preparation was constantly perfused with physiological saline solution at room temperature. To determine the ACh sensitivity of the postjunctional membrane, ACh potentials were elicited and recorded. To determine the quantum release of ACh from the motor nerve terminal and its rundown, endplate potentials (EPPs) were elicited at 2Hz and recorded. ACh sensitivity was increased with EDR and NST in a dose dependent manner. The extent of increased ACh sensitivity with EDR 10(-6)M was almost equal to that with NST 10(-7)M. In this experiment, these concentrations were used to compare the antagonistic effect of EDR and NST on the effect of dTc 10(-6)M. The depressed ACh sensitivity with dTc was reversed with EDR and NST. The extent of restoration with NST was about three times that with EDR. The quantum release of ACh was increased and rundown was depressed with EDR, but NST had no effect. After pretreatment with dTc, neither EDR nor NST increased the decreased quantum release of ACh nor reversed the enhanced rundown induced by dTc. But under the same condition, both EDR and NST reversed the ACh sensitivity depressed with dTc. These results demonstrate that neither EDR nor NST were able to affect the decreased quantum release of ACh nor the enhanced rundown induced by dTc. The results also suggest that the reversal of fade of twitch tension with EDR and NST does not always result from recovery of rundown of EPP amplitude.

Influence of extracellular calcium on the actions of guanidine at the rat neuromuscular junction.

Guanidine has been shown to potentiate neurotransmission at the skeletal neuromuscular junction. The present study was undertaken to evaluate whether reductions in extracellular calcium affect the action of guanidine on the reversal of neuromuscular blockade induced by dibekacin and d-tubocurarine in the rat phrenic-hemidiaphragm preparation. Guanidine reversed the blocking effect of d-tubocurarine, the maximal effect occurring with 3 mM at 15 min. This reversal effect of guanidine was potentiated when the extracellular calcium concentration was reduced from 2.5 mM to 1 mM and 0.3 mM. Guanidine was also effective in reversing the neuromuscular depression caused by dibekacin. In this case, it was more potent than in the d-tubocurarine-treated preparations. The maximal effect was observed with 3 mM after 15 min of exposure. When the extracellular calcium concentration was reduced from 2.5 mM to 1 mM, a potentiation of guanidine effects was observed. In this situation, the maximal effect of guanidine was observed with only 0.7 mM. However, further reductions of extracellular calcium (0.3 mM) did not show further increases. The present results show that guanidine reverses the blockade induced by dibekacin and d-tubocurarine, being more potent against the former drug. This suggests that guanidine may be useful in relieving the blockade due to a restriction of calcium entry. Its effects were potentiated when the extracellular calcium concentration was lowered to 1 mM and, in d-tubocurarine-treated muscles, to 0.3 mM. Thus, the effects of guanidine are calcium-dependent but only in a certain concentration range.

Effects of atropine, pirenzepine, imipramine and phenothiazines on the mammalian neuromuscular junction.

1. Trifluoperazine (EC50 = 11.5 nM), chlorpromazine (13.8 microM), imipramine (15 microM), atropine (75.8 microM), and pirenzepine (316.2 microM), all produced neuromuscular facilitation and antagonized the blockade produced by oxotremorine (20 and 30 microM) in the rat isolated diaphragm. 2. These antagonists did not change the responses of curarized diaphragms to direct stimulation, or the twitch tension produced by retrograde injection of acetylcholine. 3. Trifluoperazine (2.5 ng, intra-arterially) reduced the tetanic fade produced by further intra-arterial injection of d-tubocurarine (10 micrograms/kg) in the in situ cat tibial muscle. 4. These results indicate that these antagonists may interact with muscarinic autoreceptors to increase acetylcholine output in the neuromuscular junction.

Autoimmune aetiology for acquired neuromyotonia (Isaacs' syndrome)

Neuromyotonia is a rare disorder of unknown cause in which hyperexcitability of peripheral motor nerves leads to incapacitating muscle twitching, cramps, and weakness. We investigated an antibody-mediated mechanism for neuromyotonia in a 24-year-old man with a 7-year history of severe disease unresponsive to pharmacological treatment. Two periods of plasma exchange each produced almost complete disappearance of symptoms for 2-3 weeks, and a highly significant decrease in recorded neuromyotonic discharges. Injection of the patient's plasma or purified IgG into mice significantly enhanced in-vitro resistance to d-tubocurarine at the neuromuscular junction of phrenic nerve-diaphragm preparations. This finding suggests that an increase in neurotransmitter release might result from an antibody-mediated reduction in the number of functional potassium channels that normally regulate nerve excitability. The demonstration of pathogenic IgG autoantibodies in acquired neuromyotonia suggests that immunosuppressive treatment may be helpful in severe cases.

[Antagonistic effect of 4-aminopyridine derivatives on dTc induced block].

A new muscle relaxant antagonist, 4-aminopyridine (4-AMP), has various problems related to its side effects. In order to obtain 4-AMP derivatives with less side effect and the same antagonizing effect on dTc block as that of 4-AMP, three types of derivatives were synthesized. They were 4-methylaminopyridine (4-MAMP), 4-dimethylaminopyridine (4-DAMP), and 4-trimethylaminopyridine (4-TAMP). For the purpose of studying their effects on neuromuscular junction, the antagonistic effects of the three derivatives on the dTc block were compared with those of 4-AMP, by using rat diaphragm preparation in vitro, and rat sciatic nerve tibialis anterior muscle preparation in vivo. These three derivatives exhibited earlier onset time compared with 4-AMP, but their efficacy was lower in terms of ED50 in vivo and in vitro. Also their duration of effect was shorter than 4-AMP. In particular, the ED50 of 4-DAMP was much larger (9 times that of 4-AMP), and its duration of effect was shorter (11 minutes), indicating that it is unsuitable as a practical antagonistic agent. ED50 of 4-TAMP was the closest to that of 4-AMP (three times that of 4-AMP), and it exhibited effects earlier than 4-AMP (one fourth that of 4-AMP), but was inferior in duration of effect (13 minutes). With respect to antagonistic effects, these three agents cannot be described as perfect, and development of new derivatives will be required.

Influence of neostigmine on postoperative vomiting.

Thirty-eight patients undergoing elective hip or knee surgery were randomly allocated to two groups. Neuromuscular blockade in group A was antagonized with neostigmine 2.5 mg and atropine 1.2 mg, while group B received no drugs to facilitate antagonism of blockade. The incidence and severity of postoperative nausea and vomiting were assessed 24 h after operation. Nausea and vomiting were significantly reduced in group B. The incidence of nausea in group A was 68%, compared with 32% in group B (P less than 0.01). The incidence of vomiting was 47% in group A, compared with 11% in group B (P less than 0.02). A significant relationship was shown between postoperative emetic symptoms and the antagonism of neuromuscular blockade by neostigmine and atropine.

Duration of action of neostigmine and pyridostigmine in the elderly.

This study was undertaken to assess differences between young and elderly patients with respect to the duration of antagonism of metocurine neuromuscular blockade by neostigmine (NEO) or pyridostigmine (PYR). Patients were given either NEO (seven elderly and ten young) or PYR (seven elderly and eight young) and received nitrous oxide in oxygen (60:40) and 1 MAC halothane. Neuromuscular transmission was assessed by using evoked compound electromyography. Metocurine 0.1 mg/kg was given, followed by a continuous infusion to achieve 90% reduction in baseline single twitch height. After at least 30 minutes, either NEO (0.07 mg/kg) or PYR (0.14 mg/kg) and atropine (0.02 mg/kg) were given IV. After injection of NEO or PYR, the duration of maximal response (DOMR) was recorded. Mean (+/- SE) ages were 38 +/- 5 and 68 +/- 2 years in the two groups of patients receiving PYR. In the elderly, PYR significantly prolonged DOMR compared to younger patients (35.3 +/- 8.2 vs 14.4 +/- 4.2 minutes, respectively). The mean ages in the two groups of patients receiving NEO were 41.5 +/- 4 and 72 +/- 2 years. The elderly group demonstrated a significant increase in the DOMR compared to younger patients (32 +/- 10 vs 11 +/- 2 minutes, respectively). It is concluded that, compared to younger patients, the duration of action of NEO and PYR in the aged patient is prolonged.

Edrophonium-hyoscine butylbromide mixture for reversal of neuromuscular blockade: heart rate changes in infants and children.

The effectiveness of hyoscine butylbromide in the prevention of edrophonium-induced bradycardia was assessed in 50 infants and children. A mixture of edrophonium (1.0 mg/kg) and either atropine (0.01 mg/kg) or hyoscine butylbromide (0.4 mg/kg) was administered to reverse the effects of tubocurarine. An initial bradycardia followed the injection of the edrophonium-atropine mixture. In contrast there was no initial decrease in heart rate after the administration of the edrophonium-hyoscine butylbromide mixture. Hyoscine butylbromide can be used with advantage as a substitute for atropine in edrophonium reversal in infants and children.

Molecular decoys: ligand-binding recombinant proteins protect mice from curarimimetic neurotoxins.

Mimic ligand-binding sites of the nicotinic acetylcholine receptor bind d-tubocurarine and alpha-bungarotoxin in vitro. Injection of such binding sites into mice could act as molecular decoys in vivo, providing protection against toxic ligands. This hypothesis of molecular "decoyance" has been tested in greater than 250 mice. Bacterially produced cholinergic binding sites provided a 2-fold increase in the survival rate of animals challenged with curarimimetic neurotoxins. Possible considerations for decoy designs and their applications are discussed.