Effects of pancuronium and vecuronium on creatine phosphokinase in rat isolated heart, liver, kidney and diaphragm.

1. The effects of two muscle relaxants, namely, pancuronium and vecuronium, on creatine phosphokinase (CPK) release from four different types of tissues, namely, heart, liver, kidney and diaphragm, were studied in the rat in vitro. 2. The total, neat and CPK levels (units/ml), released by muscle relaxants were measured using spectrophotometric determination at 340 nm. 3. The results showed that both muscle relaxants, in low concentrations, i.e. 0.34 or 0.32 microM, close to a clinical dose of 0.1 mg/kg, had no significant effect on CPK leakage in all four types of tissues studied. However, in concentrations 12-122 times clinical dose, the two muscle relaxants produced differential adverse effects in the tissues studied. 4. In most concentrations, pancuronium and vecuronium produced significant increases in the CPK release in the kidney and diaphragm. In contrast, pancuronium had no significant effect on CPK release in the liver and the lowest effect in the heart. Similar results were obtained with vecuronium. 5. The clinical relevance and/or implications of the present results are discussed and the results are compared to those previously reported by other workers in other preparations.

Effects of pancuronium and vecuronium on plasma levels of immunoglobulins, IgG, IgM and IgE, in patients undergoing minor gynaecological surgery.

1. The effects of two competitive neuromuscular blocking agents, pancuronium and vecuronium, on plasma levels of immunoglobulins, IgG, IgM and IgE, were studied and compared, using the ELISA assay, in patients undergoing minor gynaecological surgery. 2. The results showed that neither pancuronium (0.1 mg/kg) nor vecuronium (0.1 mg/kg) had any significant effect on IgG, IgM and IgE levels in these patients. However, the underlying trend was that both pancuronium and vecuronium slightly increased the IgG and IgM levels, (by 19.5%, 22.1%, of control IgG, and by 17.3%, 28.8% of control IgM, respectively), with vecuronium being more effective than pancuronium). In addition, pancuronium, but not vecuronium, also slightly increased the IgE levels (by 5.9% of control IgE). Vecuronium, on the other hand, slightly decreased the IgE level (by 4.9% of control IgE). However, these increases or decreases were not statistically significant. 3. The significance of the present results are discussed in relation to changes in immunoglobulins and adverse effects induced by drugs, such as muscle relaxants.

Comparative effects of vecuronium and pancuronium on release of lactate dehydrogenase in rat isolated diaphragm, liver, kidney and heart.

The comparative effects of two muscle relaxants, namely pancuronium and vecuronium, on the release of intracellular lactate dehydrogenase (LDH), released from four different types of tissues, namely, the heart, liver, kidney and diaphragm, were studied in the rat in vitro. The LDH and its leakage into extracellular space, was used as an indicator for cellular membrane damage, and the aim was to see if the two muscle relaxants enhanced the release of LDH, and hence, by implication, caused adverse effects, i.e., damage to cell membrane. The total amount of LDH, the neat (LDH), and the increase in LDH release caused by different concentrations of the two muscle relaxants were measured using spectrophotometric determination at 340 nm. The results showed that both muscle relaxants, in low concentrations (0.32 or 0.34 microM, a concentration which is close to a clinical dose of 0.1 mg/ml), did not significantly enhance the LDH release from any of the 4 different types of tissues studied. However, in concentrations of 10-130 times the clinical dose, both drugs significantly enhanced the LDH release in all the 4 tissues, with pancuronium being more effective than vecuronium. In addition, the diaphragm and kidney were most affected, whereas the heart and liver being the least affected. The clinical relevance and/or implications of these comparative effects are discussed, and the results are compared to those previously reported by other workers. Pancuronium and vecuronium are among the non-depolarising neuromuscular blocking drugs currently-used in clinical anaesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of desipramine on the contractile responses to noradrenaline, clonidine and to electrical field stimulation in the rat isolated seminal vesicle.

The effect of desipramine (DMI) on the contractile responses to noradrenaline (NA), clonidine and to electrical field stimulation (FS), was studied in the rat isolated seminal vesicle. The aim was to analyse the mechanism of action of DMI in this preparation and compare the results obtained with those already published for other similar preparations, e.g. the guinea-pig seminal vesicle. The results showed that DMI, which on its own had little effect on contractility of rat seminal vesicle, significantly (P less than 0.001) enhanced the Na-induced contractions (by 30-50%), whereas it markedly reduced (by 40%) the contractions produced by clonidine. DMI also enhanced the FS-induced contractions (by about 50%) in the same preparation. The enhancement of the NA-induced responses by DMI can be explained in terms of inhibition of the NA uptake by the preparation, whereas the reduction in clonidine response may be due to blockade of adrenoceptors in the rat seminal vesicle. Other possibilities and mechanisms are also discussed in this and other types of smooth muscle preparations.

Electromagnetic stimulation blocks isometric twitch contraction in the frog sciatic nerve-gastrocnemius muscle preparation.

The effect of electromagnetic stimulation (EMS) on nerve conduction and muscle twitch contraction was studied in isolated sciatic nerve-gastrocnemius muscle of the frog. Electrical stimulation (ES) of the sciatic nerve produced twitch contractions in the gastrocnemius muscle and these responses were reduced and eventually blocked by EMS, applied to the nerve simultaneously with ES, from a d.c. source at a certain frequency and duration of the induced current. The EMS-induced inhibition of the twitch contractions was reversible, and this depended on the induced current and its duration. The possibility that other factors may have contributed to the inhibition of twitch contractions, such as a rise in temperature, was also investigated. It was concluded that EMS inhibited indirectly-elicited twitch contractions produced by ES in the frog nerve-muscle preparation.

Diaphragmatic fatigue in the rat.

We studied fatigue of rat diaphragm in response to repetitive brief and prolonged electrical stimulation of the phrenic nerve, at 0.2, 1-100 Hz. Low and high frequency of stimulation produced twitch and tetanic contractions in the rat diaphragm. A mean maximum twitch tension of 1.4 +/- 0.1 g was produced at 1 Hz, and a mean maximum tetanic tension of 5.6 +/- 0.3 g was obtained at 100 Hz (means +/- S.E., n = 8). Twitch and tetanic fatigue was produced at all frequencies of stimulations, but with different time scale, or duration, and with different number of stimuli delivered to the muscle. At low rates of stimulation, e.g. 10 Hz, fewer stimuli were needed to fatigue the muscle (3000 in 5 min), whereas at high rates of stimulation, e.g. 50 Hz, more stimuli were needed to fatigue the muscle (6600 in 2.2 min). The amplitude of the tetanic tensions elicited at 10 and 50 Hz, at the end of 5 or 2 min fatiguing stimulation, was 39 +/- 2.7% and 80 +/- 3.1% of their respective control tensions (2.8 +/- 0 2 g and 5.3 +/- 0.5 g, n = 8, P 0.001). It was concluded that fatigue in the rat diaphragm depended on the frequency and duration of stimulation as well as on the number of stimuli delivered to the muscle. Various mechanisms of muscle fatigue are described in the discussion to explain the observations made in the present investigation.

Electromagnetic stimulation and inhibition of nerve conduction in frog isolated sciatic nerve-gastrocnemius muscle preparation.

The effect of electromagnetic stimulation on nerve conduction and on muscle contraction was studied in isolated frog sciatic nerve-gastrocnemius muscle preparation. The nerve trunk was passed through an induction copper coil and current was induced from a d.c. source 1.5-4 V at a frequency of 100 min-1, for 20-120 s duration, via an operating switch. Normal indirectly-elicited twitch (0.5 Hz with 0.6 V, supramaximal, and 1 ms pulse duration) tension was elicited, repetitively, and this was interrupted by magnetic induction. Inhibition of the twitch tension was taken as a measure of conduction block. The results showed that magnetic stimulation inhibited or blocked the twitch contractions (control 3.2 +/- 0.1 g, tension, mean +/- s.e., n = 8), in 4-5 min, and hence it blocked nerve conduction in this preparation. Recovery was achieved within 4-5 min, after washing out the preparation in Ringer solution. The mechanism of inhibition was interpreted in terms of an interference with ionic fluxes across the cell membrane. A comparison of electrical and magnetic stimulation was made and this was related to their clinical and experimental implications.

Evidence that ATP and noradrenaline are released during electrical field stimulation of the rat isolated seminal vesicle.

The effects of electrical field stimulation (at 1-100 Hz with 20-25 V, supramaximal, and 0.2 ms pulse duration, for 10-20 s), on tone and contractility of rat isolated seminal vesicle was studied, in the absence and presence of specific antagonists (phentolamine, 1 microM, alpha, beta-Me-ATP, 10 microM, and verapamil, 1 microM). The aim was to provide pharmacological evidence of the release of ATP, alongside NA, during electrical stimulation of the rat seminal vesicle. Electrical field stimulation of the rat seminal vesicle produced frequency-dependent contractions. At low rates of stimulation (1-20 Hz), only small tonic contractions were observed (0.3 g tension), whereas at high rates of stimulation (80-100 Hz), only phasic contractions (2-3 g) were seen. However, at intermediate rates of stimulation (e.g. 50 Hz), a biphasic response was produced: an initial fast, twitch-like response (phasic), followed by a slow tonic contraction. The phasic contraction was blocked by the stable analogue of ATP (alpha, beta-Me-ATP), which desensitizes P2-purinoceptors. The tonic contraction is adrenergic and was blocked by phentolamine. Verapamil reduced both types of contractions in this preparation and the block was unselective on tonic versus phasic contraction. It was concluded that electrical field stimulation produced frequency-dependent contractions tonic and phasic in the rat seminal vesicle. These responses were blocked by specific antagonists, suggesting the presence of different types of neurotransmitters released during electrical stimulation of the rat seminal vesicle.

Assessment of neuromuscular blockade produced by atracurium in the rat diaphragm preparation. Measurements of tetanic fade, depression and recovery profile.

The effect of atracurium, a relatively new muscle relaxant, on neuromuscular transmission, in the rat diaphragm preparation, was studied, by analysing the characteristic features of tetanic fade and recovery pattern following a blocking concentration of atracurium (10 microns). Tetanic fade (TF) and peak tetanic tension (Tp) and its depression by atracurium, were analysed and the results were interpreted in terms of atracurium action at the neuromuscular junction. Atracurium reduced the sustained tetanic tension, elicited at 50 Hz for 0.5 s duration, and produced a marked tetanic fade in 38 s. Atracurium also reduced the peak tetanic tension by 40%, of the control value, in 38 s. Maximum tetanic tension was 5.7 g tension, and the time taken to completely block the tetanus was 4.75 +/- 0.15 min (means +/- SE, n = 8). Recovery from atracurium-induced blockade occurred in 30s (tetanic fade) and in 3-4 min (peak tetanic tension). It was concluded that atracurium produces a profound tetanic fade, at a time when the peak tetanic tension is reduced by only 40%. The data presented indicate that atracurium has a rapid onset of blockade, intermediate duration and a quick recovery profile at the rat neuromuscular junction.

Effect of noradrenaline on rubidium (86Rb) efflux in the rat isolated seminal vesicle.

The effect of noradrenaline (NA) on the efflux of rubidium (86Rb) from the rat isolated seminal vesicle was studied in the absence and presence of phentolamine and papaverine. Strips of spirally cut seminal vesicles were incubated in radioactive 86Rb (10 microCi.ml-1) for 2 h. Radioactivity was measured using an autogamma spectrometer, and the flux data were expressed in terms of rate constants per minute, of the reactive isotope efflux. A concentration-effect curve for the effect of NA on rat seminal vesicles was constructed, alone and in the presence of phentolamine (1 mumol/l) or papaverine (5 mumol/l). The results showed that NA (10-1,000 mumol/l) produced concentration-dependent contractions in the rat seminal vesicle. These responses were greatly reduced by phentolamine but markedly enhanced by papaverine. NA significantly increased 86Rb efflux from rat seminal vesicles (control rate constant 0.0042 +/- 0.001; test 0.0064 +/- 0.002, means +/- SE; n = 8 rats; p less than 0.001). This increase (52%) occurred within an exposure of 7 +/- 1 min to NA. Phentolamine decreased the NA-induced increase in 86Rb efflux, by 75 +/- 2%, whereas papaverine enhanced it by 86 +/- 5% of the control value. The mechanism of NA-induced increase in 86Rb efflux was not further investigated but was interpreted in terms of an increase in intracellular K+ (here represented by 86Rb), which will leave the cell (efflux) after initial membrane depolarization.

Comparative effects of verapamil and D-600 on the contractile responses produced by neurotransmitters and depolarizing agents in the rat isolated seminal vesicle.

1. The comparative effects of verapamil and D-600, on isometric contractions produced by noradrenaline, acetylcholine, phenylephrine, clonidine, carbachol and high potassium, were studied in rat isolated seminal vesicle. 2. The aim was to see if verapamil and D-600 differed, in their selectivity, of blocking calcium, channels, and hence inhibition of isometric contractions produced in this preparation. 3. Verapamil (1 microM) and D-600 (9.5 microM), selectively, reduced the isometric contractions, greater reductions occurred in the KCl-induced contractions (control EC50 19 +/- 1.5 mM, in verapamil 58 +/- 1.3 mM, and in D-600 37 +/- 2.0 mM, means +/- SE, n = 8, P less than 0.001, less than 0.01, respectively). 4. It was concluded that KCl-induced contractions were voltage-dependent, whereas noradrenaline operated via both voltage and receptor-mediated mechanisms. 5. The clinical relevance of these results was discussed, and it may help our current understanding of the pharmacological management of sexual dysfunction.

The effect of ethanol on rat vas deferens.

The effect of ethanol (3.9-390 mM) on resting tension of vas deferens, isometric contractions produced by field stimulation of the vas deferens and on the contractions produced by neurotransmitters, acetylcholine (ACh 0.55-55 mM), noradrenaline (NA 0.058-580 microM) and 5-hydroxytryptamine(5-HT 0.25-250 microM) was studied in rat vas deferens to see if ethanol modified neurotransmission and muscle contraction in this preparation. The results showed that ethanol had no significant effect on resting tension of the muscle, but reduced the contractions produced by field stimulation and by neurotransmitters. It was concluded that ethanol modifies neurotransmission in the rat vas deferens preparation, by reducing the contractions produced by field stimulation and by depolarizing agents.

Inhibition of nerve conduction by electromagnetic induction of the frog sciatic nerve-gastrocnemius muscle preparation.

The effect of electromagnetic induction (EMI) on impulse conduction and muscle contraction was studied in isolated sciatic nerve-gastrocnemius muscle preparation of the frog. Electrical stimulation (ES) of the sciatic nerve, at 0.5 Hz with 0.6 V (supramaximal) and 1-ms pulse duration, produced twitch contractions (3.5 +/- 0.4 g tension, mean +/- S.E., n = 8 frogs), which were reduced or blocked by EMI, applied to the nerve via an induction coil, from a d.c. source of 1.5-4 V, at a frequency of 100 min-1, for 2- to 4-min duration. Recovery of the blocked twitches was obtained within 4-5 min, after the cessation of the EMI and washing out the preparation in Ringer solution. The inhibition of the twitch tension by EMI was compared to that produced by an effective concentration of a local anaesthetic, lignocaine (1 microM), which is known to block conduction, by blocking ionic fluxes across the nerve membrane. It is possible that EMI also interferes with the ionic fluxes, and in prolonged duration, may produce changes in the myelin sheath (or the Schwann cells) of the nerve membrane. A comparison of ES with EMI was made, and it was concluded that EMI inhibited electrically induced neuromuscular transmission at the frog neuromuscular junction.

Tetanic fade following atracurium-induced neuromuscular blockade in the rat diaphragm preparation.

1. The effect of atracurium on neuromuscular transmission was studied in the rat diaphragm preparation, by analysing the characteristics of tetanic fade and its recovery profile after using a blocking concentration of atracurium (10 mumol.litre-1). 2. Tetanic fade (TF), peak tetanic tension (Tp), and its depression, and end tetanic tension (Te), sustained tension, were analysed and compared to their respective control values before administration of atracurium. 3. The results showed that atracurium reduced the tetanic tension, i.e., the peak and end tetanic tensions, elicited at 50 Hz for 0.5 s duration, and produced a marked tetanic fade, which was developed fully in about 38 s. On the other hand, the peak tetanic tension (Tp) was only reduced by 40% (at 38 s) of its control value (5.7 g tension). The time taken to completely block Tp was about 5 min. 4. After washing out atracurium, recovery of the peak tetanic tension occurred within 3-4 min., while tetanic fade was reversed within 30 s. 5. It was concluded that atracurium produces a profound tetanic fade, at a time when the peak tetanic tension is only depressed by about 40% of the control value. The results indicated that atracurium had a powerful neuromuscular blocking action at the rat diaphragm preparation.

Effect of ethanol on neuromuscular function in the rat diaphragm preparation.

The effect of ethanol on neuromuscular transmission in the isolated phrenic nerve-diaphragm preparation of the rat was studied by analysing its effect on directly- and indirectly-elicited twitch tension, tetanic and post-tetanic twitch tensions, and on the phenomenon of post-tetanic twitch potentiation (PTP). The results show that ethanol (1.0 X 10(-4)-1.0 M) depresses neuromuscular transmission, by reducing the amplitudes of both directly and indirectly elicited twitch and tetanic contractions. Ethanol produces a greater reduction in the amplitude of indirectly- than directly-elicited twitch tension and the mean concentration of ethanol which produced a 50% reduction was 38 mM. High concentrations of ethanol (greater than 10(-3) M) completely blocked the indirectly-elicited twitch tension in 4 min exposure. Ethanol also reduced the tetanic tension and increased the PTP value. There was no tetanic fade in the presence of ethanol, but the peak tetanic tension was reduced by 20-50%. It is suggested that ethanol inhibits neuromuscular transmission in the rat phrenic nerve-diaphragm preparation, possibly via a mixture of pre- and postjunctional mechanisms and produces a greater reduction in the twitch than tetanic tension.