Procaine and mepivacaine have less toxicity in vitro than other clinically used local anesthetics

The neurotoxicity of local anesthetics can be demonstrated in vitro by the collapse of growth cones and neurites in cultured neurons. We compared the neurotoxicity of procaine, mepivacaine, ropivacaine, bupivacaine, lidocaine, tetracaine, and dibucaine by using cultured neurons from the freshwater snail Lymnaea stagnalis. A solution of local anesthetics was added to the culture dish to make final concentrations ranging from 1 x 10(-6) to 2 x 10(-2) M. Morphological changes in the growth cones and neurites were observed and graded 1 (moderate) or 2 (severe). The median concentrations yielding a score of 1 were 5 x 10(-4) M for procaine, 5 x 10(-4) M for mepivacaine, 2 x 10(-4) M for ropivacaine, 2 x 10(-4) M for bupivacaine, 1 x 10(-4) M for lidocaine, 5 x 10(-5) M for tetracaine, and 2 x 10(-5) M for dibucaine. Statistically significant differences (P < 0.05) were observed between mepivacaine and ropivacaine, bupivacaine and lidocaine, lidocaine and tetracaine, and tetracaine and dibucaine. The order of neurotoxicity was procaine = mepivacaine < ropivacaine = bupivacaine < lidocaine < tetracaine < dibucaine. Although lidocaine is more toxic than bupivacaine and ropivacaine, mepivacaine, which has a similar pharmacological effect to lidocaine, has the least-adverse effects on cone growth among clinically used local anesthetics. IMPLICATIONS: Systematic comparison was assessed morphologically in growth cones and neurites exposed to seven local anesthetics. The order of neurotoxicity was procaine = mepivacaine < ropivacaine = bupivacaine < lidocaine < tetracaine < dibucaine. Although lidocaine is more toxic than bupivacaine and ropivacaine, mepivacaine, which has a similar pharmacological effect to lidocaine, is the safest among clinically used local anesthetics.     

Suppression of acetylcholine-induced relaxation by local anesthetics and vascular NO-cyclic GMP system

Background: Local anesthetics have been demonstrated to attenuate acetylcholine-induced relaxation of vascular smooth muscle, but the mechanism responsible has not been elucidated. The present study was undertaken to ascertain whether this effect of local anesthetics is due to suppression of the vascular nitric oxide (NO)-cyclic GMP (cGMP) system. Methods: Isolated rat aortae were cut into helical strips and mounted in bathing solution to measure isometric tension changes. They were precontracted with phenylephrine (0.3 μM)then exposed to cumulative concentrations of relaxants including acetylcholine, sodium nitroprusside (SNP) and papaverine, in the absence or presence of local anesthetics. Aortaefor cGMP measurements were cut longitudinally into pairs of strips and bathed in the solution without tension. In the absence or presence of anesthetics, they were stimulated with acetylcholine or SNP, and the cGMP content of each strip was radioimmunoassayed. Results: Acetylcholine-induced, endothelium-dependent relaxation of phenylephrine-precontracted aortae was attenuated by lidocaine (30–300 μM), tetracaine (10–30 μM), bupivacaine (10–100 μM) and ropivacaine (30–100 μM). SNP-inducedrelaxation was attenuated by lidocaine (300 μM), tetracaine (30 μM), bupivacaine (10–100 μM) and ropivacaine (30–100 μM). Papaver-ine-induced relaxation was attenuated by lidocaine (300 μM), bupivacaine (30–100 μM) and ropivacaine(30–100 μM), and augmented by tetracaine (30 μM). Cyclic GMP levels in acetylcho-line-stimulated aortae were reduced significantly by lidocaine (300 μM), tetracaine(100 μM) and bupivacaine (300 μM) treatment, but not by ropivacaine (300 μM). SNP-stimulated cGMP levels were reduced by tetracaine (100 μM) but not by any other anesthetics at the concentrations tested. Conclusion: We conclude that lidocaine, tetracaine and bupivacaine suppress acetylcholme-stimulated formation of cGMP. However, the attenuation of acetylcholine-induced relaxation by local anesthetics is not totally ascribable to reduced cGMP levels.     

A comparison of the neurotoxic effects on the spinal cord of tetracaine,lidocaine, bupivacaine,and ropivacaine administered intrathecally in rabbits

We have reported that increased glutamate concentrations in microdialysate of the cerebrospinal fluid (CSF) may be clue phenomena to elucidate mechanisms of neurotoxicity of intrathecal tetracaine. However, little is known about whether this is true for other local anesthetics. In this study, we compared the effects of local anesthetics on glutamate concentrations in CSF microdialysate and neurologic and histopathologic outcome. Rabbits were assigned into 5 groups (n = 6 in each) and intrathecally received 0.3 mL of NaCl solution (control), 2% tetracaine, 10% lidocaine, 2% bupivacaine, or 2% ropivacaine. Neurologic and histopathologic assessments were performed 1 wk after the administration. Intrathecal local anesthetics significantly increased glutamate concentrations with no significant differences among the four local anesthetics. The sensory and motor functions in the lidocaine group were significantly worse than in the other groups. Characteristic histopathologic changes were vacuolation in the dorsal funiculus and chromatolytic damage of motor neurons. The extent of vacuolation of the dorsal funiculus was in the order of lidocaine = tetracaine > bupivacaine > ropivacaine. Although the differences among the local anesthetics cannot be explained by glutamate concentrations, the results suggest that the margin of safety may be smallest with lidocaine. IMPLICATIONS: Large concentrations of local anesthetics administered intrathecally increased glutamate concentrations in the cerebrospinal fluid. The margin of safety may be smallest with lidocaine.     

Comparative inotropic effects of local anesthetics in isolated cat papillary muscles

The direct inotropic action of seven local anesthetics: procaine, mapivacaine, lidocaine, tetracaine, chloroprocaine, bupivacaine and etidocaine were compared in isolated cat papillary muscles. All of the local anesthetics produced a dose-related depression of maximal velocity of shortening (Vmax), maximal developed force (Fm) and maximal dF/dt. The more potent local anesthetics such as bupivacaine and etidocaine depressed myocardial contractility at significantly lower concentrations than the less potent local anesthetics such as lidocaine and mepivacaine. Depression of Vmax by bupivacaine or etidocaine was three times greater than that by lidocaine and ten times greater than that by procaine. At the same concentration (10^–4M), direct myocardial depression was demonstrated in the following order of severity: etidocaine bupivacaine tetracaine chloroprocaine lidocaine mepivacaine procaine.(Kemmotsu O, Nakata F, Ueda M, et al.: Comparative inotropic effects of local anesthetics in isolated cat papillary muscles. J Anesth 4: 1–8, 1990)     

Comparative CNS toxicity of lidocaine, etidocaine, bupivacaine, and tetracaine in awake dogs following rapid intravenous administration

The comparative central nervous system (CNS) toxicity of serially administered intravenous doses of lidocaine, bupivacaine, etidocaine, and tetracaine was investigated in awake dogs. The mean cumulative dose required for convulsive activity was 4.0 mg/kg tetracaine, 5.0 mg/kg bupivacaine, 8.0 mg/kg etidocaine, and 22.0 mg/kg lidocaine. The cumulative convulsive dose of lidocaine was significantly greater than that of the other three agents (P less than 0.01). A comparison of the in vivo anesthetic potency and the acute CNS toxicity of these various agents suggests little difference in the therapeutic ratio between less potent anesthetics such as lidocaine and more potent drugs, i.e., tetracaine, bupivacaine, and etidocaine. The relative CNS toxicity of the different agents as determined in awake dogs in this study was compared with their relative cardiovascular toxicity previously evaluated in a series of ventilated dogs anesthetized with pentobarbital. The dose of lidocaine, etidocaine, tetracaine, and bupivacaine required to produce irreversible cardiovascular depression was 3.5-6.7 times greater than that which produced convulsions. These results suggest that the CNS is the primary target organ for the toxic effects of both highly lipid-soluble and highly protein-bound local anesthetics (i.e., bupivacaine, etidocaine, and tetracaine) and less lipid-soluble and less protein-bound drugs (i.e., lidocaine) following rapid intravenous administration.     

Carbachol-induced sustained tonic contraction of rat detrusor muscle.

OBJECTIVE: To investigate the underlying contractile mechanism of the sustained tonic contraction (SuTC) induced by repetitive carbachol application in rat detrusor muscles. MATERIALS AND METHODS: Longitudinal muscle strips with no mucosa were obtained from the anterior wall of the urinary bladder in 12-week-old Sprague-Dawley rats. Carbachol (5 micromol/L) was applied repetitively to induce SuTC. The carbachol-induced SuTC was assessed in the presence of various Ca2+-channel blockers and drugs affecting intracellular Ca2+ concentration. RESULTS: The first application of carbachol elicited a large phasic contraction followed by a tonic contraction (TC); the carbachol-induced contraction was completely reversed by washing out the solution. However, the initial phasic contraction was not reproduced after a second or further application of carbachol. There was consistently only a SuTC with no phasic contraction. The amplitude of the SuTC was 85% of the TC induced by the first carbachol application. The application of atropine (1 micromol/L) to the bath completely blocked SuTC. The carbachol-induced SuTC was insensitive to nicardipine (5 micromol/L) and extracellular polyvalent cations (1 mmol/L, La3+, Co2+, Cd2+, Ni2+ ). Moreover, a similar SuTC was induced even after the complete elimination of extracellular Ca2+ by adding 2 mmol/L EGTA to the Ca2+-free Tyrode solution. To exclude intracellular Ca2+ sources related to the sarcoplasmic reticulum (SR), the effects of SR Ca2+ pump inhibitors, cyclopiazonic acid (CPA, 10 micromol/L) and thapsigargin (0.5 micromol/L) were tested. The carbachol-induced SuTC was insensitive to pretreatment with CPA and/or thapsigargin. To deplete the ryanodine-sensitive Ca2+ pool, muscle strips were repetitively stimulated with caffeine (10 mmol/L) in the presence of 10 micromol/L ryanodine, which did not affect the carbachol-induced SuTC. CONCLUSIONS: Although the characteristics of the carbachol-induced SuTC have not been defined, these results show that a significant proportion of the carbachol-induced contraction in rats is contributed by the SuTC, which is present even in the complete absence of external Ca2+. The SuTC was not affected by limiting the contributions of internal Ca2+ sources. This suggests that the SuTC in rat bladders is unrelated to known Ca2+ mobilization mechanisms.     

An electrophysiological study of ropivacaine on excised cervical vagus nerves of rabbit]

Ropivacaine, a new long acting local anaesthetic of amide type is structurally related to mepivacaine and bupivacaine. This study was designed to compare the in vitro potency and neurotoxicity of ropivacaine with those of other commercially available local anaesthetics using an isolated rabbit vagus nerve model. Ropivacaine dose-dependently suppressed the evoked compound action potentials of A beta nerve and C nerve components. Minimum concentration of ropivacaine for producing complete suppression of the compound action potentials of all components was 0.008%. Electron microscopic observation showed that ropivacaine did not destroy any peripheral nervous structures in concentrations up to 0.75%. When the neurotoxic effect of ropivacaine was compared, in terms of risk ratio (clinically used concentration/concentrations producing 2 hr irreversible block), with that of commercially available local anesthetics, the rank oder was dibucaine, tetracaine, lidocaine, bupivacaine and ropivacaine.     

Pharmacological effects of propiverine and its active metabolite, M-1, on isolated human urinary bladder smooth muscle, and on bladder contraction in rats

Objective:   To investigate the effects of M-1, a major active metabolite of propiverine on the bladder.
Methods:   We have evaluated the effects of M-1 on the contractions induced by carbachol, KCl, CaCl₂, and electrical field stimulation (EFS) in human detrusor smooth muscles, and pelvic nerve stimulation-induced bladder contractions in rats. The effects of M-1 were also compared with the effects of propiverine and tolterodine.
Results:   Pretreatment with propiverine and tolterodine caused parallel shifts to the right of the concentration-response curves to carbachol. M-1 caused concentration-dependent reduction in the maximum contractile responses induced by carbachol. Although tolterodine did not inhibit the KCl- and CaCl₂-induced contractions, M-1 and propiverine significantly inhibited these contractions. In the presence of atropine, M-1 and propiverine significantly inhibited the atropine resistant part of the contraction induced by EFS. On the other hand, tolterodine did not have significant inhibitory effects on atropine resistant contractions. Pelvic nerve stimulation induced bimodal phasic and tonic contractions in the rat bladder. M-1 mainly inhibited the phasic contraction. Tolterodine caused a significant inhibition in the tonic contraction, and propiverine had inhibitory effects on both contractions.
Conclusions:   The present results suggest that M-1 has inhibitory effects on the bladder smooth muscles through calcium antagonistic action. It is possible that the clinical effects of propiverine on the human bladder are based not only on the action of propiverine itself but also on one of its active metabolites, M-1.     

Comparisons of the anesthetic potency and intracellular concentrations of S(-) and R() bupivacaine and ropivacaine in crayfish giant axon in vitro

Levobupivacaine and ropivacaine are both single S(-) enantiomers that have less severe cardiotoxic and convulsant effects than racemic bupivacaine. We compared the anesthetic actions of S(-) bupivacaine, R(+) bupivacaine, and ropivacaine in vitro by studying their effects on action potential amplitude and the maximal rate of rise of action potential in crayfish giant axon. To clarify the difference of intracellular anesthetic concentration, the intracellular ionized anesthetic concentration was measured. Desheathed crayfish axons were stimulated at a frequency of either 0. 1 or 5 Hz and perfused with 1 mM of each anesthetic at pH 7.0. Intracellular anesthetic concentration was measured by us- ing local anesthetic-sensitive glass microelectrodes. At 0.1-Hz stimulation, no differences were observed in their potency. At 5-Hz stimulation, the order of magnitude of the mean percentage decrease in maximal rate of rise of action potential was S(-) bupivacaine > R(+) bupivacaine > ropivacaine. Intracellular local anesthetic concentration did not differ among the three anesthetics at 0.1 Hz and 5 Hz. We conclude that, compared with ropivacaine, S(-) bupivacaine has a more potent phasic blocking effect in crayfish giant axon. The intracellular local anesthetic concentrations of S(-), R(+) bupivacaine and ropivacaine were not significantly different, regardless of differences in blocking effect and stimulation frequency. IMPLICATIONS: S(-) bupivacaine has a more potent phasic blocking effect than ropivacaine or R(+) bupivacaine in crayfish giant axons in vitro. An equivalent intracellular local anesthetic concentration for the three anesthetics was found, suggesting that the intracellular cationic local anesthetic concentration is not directly correlated with the intensity of block.     

Comparison of toxicity effects of ropivacaine,bupivacaine, and lidocaine on rabbit intervertebral disc cells in vitro

Background contextIt has been shown that bupivacaine, the most commonly used local anesthetic to relieve or control pain in interventional spine procedures, is cytotoxic to intervertebral disc (IVD) cells in vitro. However, some other common local anesthetics, such as ropivacaine and lidocaine, are also frequently used in the treatment of spine-related pain, and the potential effects of these agents remain unclear.PurposeThe purpose of this study was to evaluate the effect of various local anesthetics on rabbit IVD cells in vitro and further compare the cytotoxicity of ropivacaine, bupivacaine, lidocaine, and saline solution control.Study designControlled laboratory study.SubjectsRabbit annulus fibrosus (AF) and nucleus pulposus (NP) cells were isolated from Japanese white rabbits.MethodsBoth AF and NP cells at the second generation maintained in monolayer were exposed to various concentrations of local anesthetics (eg, bupivacaine) or different durations of exposure and evaluated for cell viability by use of cell counting kit-8 (CCK-8). In addition, to compare the cytotoxicity of ropivacaine, bupivacaine, lidocaine, and saline solution control in commercial concentration, the viability was analyzed by flow cytometry after 60-minute exposure, and the morphologic changes were observed by the phase-contrast microscopy. Apoptosis and necrosis of IVD cells were confirmed by using fluorescence microscopy with double staining of Hoechst 33342 and propidium iodide.ResultsRabbit IVD cell death demonstrated a time and dose dependence in response to bupivacaine and lidocaine. However, ropivacaine only exerted a significant time-dependent effect on IVD cells. There was no significant difference in IVD viability after treatment with different doses of ropivacaine. In addition, the results showed that lidocaine was the most toxic of the three local anesthetics and that ropivacaine presented less cytotoxicity than lidocaine and bupivacaine. Fluorescence microscopy also confirmed that the short-term toxic effect of local anesthetics on both AF and NP cells was mainly caused by necrosis rather than apoptosis.ConclusionsResults show that bupivacaine and lidocaine decrease cell viability in rabbit IVD cells in a dose- and time-dependent manner. All local anesthetics should be avoided if at all possible. Ropivacaine may be a choice if necessary, but it is also toxic. The increase in cell death is more related with cell necrosis rather than cell apoptosis. If these results can be corroborated in tissue explant models or animal studies, caution regarding diagnosing, treating, and controlling spine-related pain with local anesthetics is prompted.     

The inhibition of the N-methyl-D-aspartate receptor channel by local anesthetics in mouse CA1 pyramidal neurons.

Although the effects of local anesthetics on sodium channels and various other channels and receptors have been intensively investigated, there is little information available about their effects on N-methyl-D-aspartate (NMDA) receptors. We examined the effects of four local anesthetics (procaine, tetracaine, bupivacaine, and lidocaine) on NMDA-induced currents by using a whole-cell patch-clamp technique in dissociated mouse hippocampal pyramidal neurons. Procaine and tetracaine produced a reversible and concentration-dependent inhibition of NMDA-induced currents, but lidocaine showed little inhibition at 1 mM or less. The half-maximal inhibition values (mM; mean +/- SEM) for procaine, tetracaine, bupivacaine, and lidocaine at -60 mV were 0.296 +/- 0.031, 0.637 +/- 0.044, 2.781 +/- 0.940 (extrapolated data), and 7.766 +/- 14.093 (extrapolated data), respectively. Procaine 0.2 mM reduced the maximal NMDA-induced currents without affecting the 50% effective concentration values for NMDA. The inhibition by procaine exhibited voltage dependence and was more effective at negative potentials. These results indicate a noncompetitive antagonism of procaine on NMDA receptors and suggest that the inhibition is the result of a channel-blocking mechanism. IMPLICATIONS: We examined the effects of four local anesthetics (procaine, tetracaine, bupivacaine, and lidocaine) on NMDA-induced currents by using a whole-cell patch-clamp technique in dissociated mouse hippocampal pyramidal neurons. Both procaine and tetracaine produced a reversible and concentration-dependent inhibition of the NMDA-induced currents.     

The neurotoxicity of local anesthetics on growing neurons: a comparative study of lidocaine, bupivacaine, mepivacaine, and ropivacaine.

Local anesthetics can be neurotoxic. To test the hypothesis that exposure to local anesthetics produces morphological changes in growing neurons and to compare this neurotoxic potential between different local anesthetics, we performed in vitro cell biological experiments with isolated dorsal root ganglion neurons from chick embryos. The effects of lidocaine, bupivacaine, mepivacaine, and ropivacaine were examined microscopically and quantitatively assessed using the growth cone collapse assay. We observed that all local anesthetics produced growth cone collapse and neurite degeneration. However, they showed significant differences in the dose response. The IC(50) values were approximately, 10(-2.8) M for lidocaine, 10(-2.6) M for bupivacaine, 10(-1.6) M for mepivacaine, and 10(-2.5) M for ropivacaine at 15 min exposure. Some reversibility was observed after replacement of the media. At 20 h after washout, bupivacaine and ropivacaine showed insignificant percentage growth cone collapse in comparison to their control values whereas those for lidocaine and mepivacaine were significantly higher than the control values. Larger concentrations of the nerve growth factor (NGF) did not improve this reversibility. In conclusion, local anesthetics produced morphological changes in growing neurons with significantly different IC(50). The reversibility of these changes differed among the four drugs and was not influenced by the NGF concentration. IMPLICATIONS: Local anesthetics induce growth cone collapse and neurite degeneration in the growing neurons. Mepivacaine was safer than lidocaine, bupivacaine, and ropivacaine for the primary cultured chick neurons.     

Local anesthetics impair human granulocyte phagocytosis activity,oxidative burst,and CD11b expression in response to Staphylococcus aureus

BACKGROUND: With invasion of bacteria, the host defense system is activated by a complex cascade of various mechanisms. Local anesthetics previously were shown to interact with diverse components of the immune response, such as leukocyte adherence on endothelial monolayers, oxidative burst, or crosstalk within lymphocyte subset populations. However, effects of newer local anesthetics like bupivacaine and ropivacaine on antibacterial host defense-primarily phagocytosis activity, oxidative burst, or CD11b expression-still remain unclear. METHODS: Whole blood samples were preincubated with local anesthetics (lidocaine, 9.2, 92.2, and 1,846 microm bupivacaine, 6.1, 61, and 770 microm; ropivacaine, 6.4, 64, and 801 microm). For the oxidative burst and CD11b assay, dihydroethidium was added to the probes. After viable Staphylococcus aureus was added in a 5 to 1 ratio following leukocyte count, phagocytosis was stopped at different times, and staining with monoclonal antibodies was performed for subsequent flow cytometric analysis of phagocytosis activity, oxidative burst, and CD11b expression. RESULTS:Granulocyte phagocytosis activity, CD11b expression, and generation of reactive oxygen species were significantly reduced by lidocaine (P < 0.0002) and bupivacaine (P < 0.005) in the highest concentration (1,846 microm and 770 microm, respectively). The capability of granulocytes to ingest bacteria was significantly depressed only by lidocaine (P < 0.003). Ropivacaine had no significant effect on any parameter investigated. CONCLUSIONS: Local anesthetic dose and structure dependently inhibit inflammatory and immunologic parameters of granulocyte functions. Ropivacaine shows low interference with granulocyte immunologic and inflammatory functions.     

Local anesthetic-induced protection against lipopolysaccharide-induced injury in endothelial cells: the role of mitochondrial adenosine triphosphate-sensitive potassium channels

Lidocaine attenuates cell injury induced by ischemic-reperfusion and inflammation, although the protective mechanisms are not understood. We hypothesized that lidocaine and other amide local anesthetics protect against endothelial cell injury through activation of the mitochondrial adenosine triphosphate-sensitive potassium (mitoK(ATP)) channels. We determined the effects of amide local anesthetics (lidocaine, ropivacaine, and bupivacaine), ester local anesthetics (tetracaine and procaine), one amide analog (YWI), and two non-amide local anesthetic analogs (JDA and ICM) on viability of human microvascular endothelial cells after exposure to lipopolysaccharide (LPS) in the absence or presence of the mitoK(ATP) channel antagonist 5-hydroxydecaonate. Flavoprotein fluorescence was used to investigate the effects of local anesthetics on diazoxide-induced activation of mitoK(ATP) channels. Lidocaine, ropivacaine, bupivicaine, YWI, JDA, and ICM attenuated by 60% to 70% the decrease in cell viability caused by LPS. Amide local anesthetics and YWI protection was inhibited by 5-hydroxydecaonate, whereas the protection induced by JDA and ICM was not. Tetracaine and procaine did not protect against LPS-induced injury. The amide local anesthetics and the amide analog (YWI) enhanced diazoxide-induced flavoprotein fluorescence by 5% to 20%, whereas ester local anesthetics decreased diazoxide-induced flavoprotein fluorescence by 5% to 60% and the non-amide local anesthetic analogs had no effect. In conclusion, amide local anesthetics and the amide analog (YWI) attenuate LPS-induced cell injury, in part, through activation of mitoK(ATP) channels. In contrast, tetracaine and procaine had no protective effects and inhibited activation of mitoK(ATP) channels. The non-amide local anesthetic analogs induced protection but through mechanisms independent of mitoK(ATP) channels.     

Local anesthetics have different mechanisms and sites of action at recombinant 5-HT3 receptors

BACKGROUND AND OBJECTIVES: In addition to their blockade of voltage-dependent sodium channels, the action of local anesthetics at 5-hydroxytryptamine-3 (5-HT3) receptors may be clinically relevant. Because local anesthetics have different clinical properties, we have tested the hypothesis that differences in interactions at the 5-HT3 receptor may be clinically relevant by investigating the effects of 4 local anesthetics on recombinant wild-type and 4 mutant 5-HT3A receptors. METHODS: The cRNAs from human wild-type and 4 mutant 5-HT3A subunit clones were synthesized in vitro and expressed in Xenopus oocytes. Four mutant receptors were obtained by site-directed mutagenesis in the N-terminal extracellular region, which contains the agonist binding domain. Tryptophan (W) at positions 62 and 155 were replaced by tyrosine (Y) and glutamate (E) at position 101 by aspartate (D) or asparagine (N). The 2-electrode voltage clamp technique was used to measure peak currents induced by 5-HT in these receptors in the presence and absence of local anesthetics. RESULTS: All local anesthetics inhibited 5-HT-induced currents in a dose-dependent manner in the wild-type receptor. Inhibition by procaine and tetracaine were competitive whereas those of bupivacaine and lidocaine were both noncompetitive and competitive. The 4 mutants (W62Y, W155Y, E101D, E101N) could all form functional receptors. All mutant receptors exhibited a major increase (> 10-fold) in the half-maximum inhibitory concentration for procaine. The half-maximum inhibitory concentrations of tetracaine, bupivacaine, and lidocaine in mutant receptors were increased 2- to 3-fold except that of tetracaine in W62Y receptor (6-fold). CONCLUSIONS: The ester type local anesthetics, procaine and tetracaine, may act at a different site on the 5-HT(3A) receptor and with a different mechanism than the amide-type local anesthetics. Clinical differences between local anesthetics may be at least partially due to differences in interactions at the 5-HT3A receptor.     

Blockade of Na sup + and K sup + Currents by Local Anesthetics in the Dorsal Horn Neurons of the Spinal Cord

Background: The dorsal horn of the spinal cord is a pivotal point for transmission of neuronal pain. During spinal and epidural anesthesia, the neurons of the dorsal horn are exposed to local anesthetics. Unfortunately, little is known about the action of local anesthetics on the major ionic conductances in dorsal horn neurons. In this article, the authors describe the effects of bupivacaine, lidocaine, and mepivacaine on voltage-gated Na sup + and K sup + currents in the membranes of these neurons.

Methods: The patch-clamp technique was applied to intact dorsal horn neurons from laminae I-III identified in 200-micro meter slices of spinal cord from newborn rats. Under voltage-clamp conditions, the whole-cell Na sup + and K sup + currents activated by depolarization were recorded in the presence of different concentrations of local anesthetics.

Results: Externally applied bupivacaine, lidocaine, and mepivacaine produced tonic block of Na sup + currents with different potencies. Half-maximum inhibiting concentrations (IC50) were 26, 112, and 324 micro Meter, respectively. All local anesthetics investigated also showed a phasic, that is, a use-dependent, block of Na sup + channels. Rapidly inactivating K sup + currents (KA currents) also were sensitive to the blockers with IC50 values for tonic blocks of 109, 163, and 236 micro Meter, respectively. The block of KA currents was not use dependent. In contrast to Na sup + and KA currents, delayed-rectifier K sup + currents were almost insensitive to the local anesthetics applied.     

A comparison of intracellular lidocaine and bupivacaine concentrations producing nerve conduction block in the giant axon of crayfish in vitro

Clinically, lidocaine requires a larger concentration than bupivacaine to block nerves. Bupivacaine has a higher lipid solubility, tissue permeability, and affinity for sodium channels than lidocaine, resulting in greater anesthetic potency. Local anesthetics require access to the sodium channel from the intracellular milieu. In this study, we sought to determine the intracellular concentration of lidocaine and bupivacaine when a nerve was blocked in the giant axon of a crayfish. A solution of lidocaine or bupivacaine was perfused, and a nerve block was determined as the absence of an evoked action potential after tonic or phasic electrical stimulation. The intracellular lidocaine or bupivacaine concentration was measured using a lidocaine- or bupivacaine-sensitive glass micro-electrode. A phasic block was more effectively and rapidly achieved with a smaller concentration of bupivacaine than with lidocaine. The intracellular concentration and intra- to extracellular ratios were significantly larger with lidocaine than with bupivacaine when nerve conduction was blocked. These findings suggest that bupivacaine has a higher potency than lidocaine, at least in the giant axon of a crayfish in vitro. The implications of the present results are that bupivacaine is a more potent nerve block and produces a use-dependent (phasic) block at smaller concentrations than lidocaine.     

The effects of bupivacaine, ropivacaine and mepivacaine on the contractility of rat myometrium

Local anesthetic agents are commonly used for obstetric anesthesia and analgesia. We determined the effects of bupivacaine, ropivacaine and mepivacaine on the contractility of isolated pregnant rat uterine muscle strips. Uterine specimens were obtained from 18- to 21-day pregnant Wistar rats (n = 28). Myometrial strips were obtained from the uterine horns after removing the fetuses and non-uterine tissue, incubated in organ baths and contractions stimulated with oxytocin. When contractions became regular, strips were exposed to increasing concentrations of the study drugs. Mepivacaine (n = 8), ropivacaine (n = 10) and bupivacaine (n = 10) were used at cumulative doses from 10(-8) to 10(-4) mol/L. Two of the local anesthetics, bupivacaine most, ropivacaine least, caused a dose-dependent inhibition of uterine contractility. In contrast, mepivacaine significantly increased uterine contractility. Bupivacaine, ropivacaine and mepivacaine were found to have no effect on frequency of uterine contractions. These results demonstrate that bupivacaine and ropivacaine may inhibit myometrium contractility.     

Variations in carbachol- and ATP-induced contractions of the rat detrusor: effects of gender, mucosa and contractile direction

Purpose

Contractile characteristics of the bladder may depend on variables such as gender, mucosa (MU) and direction of the contractions. However, definitive information is not yet available despite earlier studies on the effects of one variable or another. Here, we explored the differences in the rat detrusor attributable to gender, mucosa and contractile direction.

Methods

K⁺, carbachol (CCh) and ATP were used as contractile stimuli on rat detrusor strips with and without MU. Contractility was monitored using a myograph system. Both tonic and phasic contractile activities were analyzed.

Results

MU-independent contractions induced by CCh were more potent in females, an effect specific to the longitudinal direction only. The maximal CCh response was larger also in females when MU was removed, suggesting a stronger MU-independent component in the contraction. The larger area under curves of the females under ATP stimulation showed dependence on MU and contractile direction as well. ATP-induced contractions in the males were affected more by MU in the transverse direction than in the females. Direction- and MU-dependent variability of ATP responses was also observed in the males but not in females.

Conclusions

Findings here added new information to the understanding of bladder contractile physiology, providing insights into the quest for better drugs in managing bladder disorders.     

Local anesthetics potentiate nitric oxide synthase type 2 expression in rat glial cells

Expression of the calcium-independent nitric oxide synthase (NOS2) contributes to damage in neurologic disease and trauma. The effects of local anesthetics on NOS2 expression have not been examined. The authors tested the effects of four local anesthetics on the expression of NOS2 in immunostimulated rat C6 glioma cells. Incubation with local anesthetics alone did not induce nitrite accumulation; however, the nitrite production induced by stimulation with bacterial endotoxin lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) was increased in a dose-dependent manner by bupivacaine (maximal 3-fold at 360 microM), tetracaine (maximal 7-fold at 360 microM), and lidocaine at higher doses (5-fold increase at 3.3 mM). Significant increases in nitrite production were observed in concentrations of bupivacaine or tetracaine as low as 120 microM, which correspond to 30 microg/mL (.003% weight/volume). In contrast, ropivacaine had little effect on nitrite production (160% of control values) and only at the highest concentration (3.3 mM, corresponding to 890 microg/mL or 0.089% w/v) tested. Increased nitrite production was not caused by cytotoxic effects of the drugs used, as assessed by release of intracellular lactate dehydrogenase. Increased nitrite production was accompanied by increased NOS2 catalytic activity, steady state mRNA levels, and promoter activation. These results demonstrate that submillimolar doses of two commonly used local anesthetics can increase glial NOS2 expression.