Effects of modulators of sarcoplasmic Ca2+ release on the development of skeletal muscle fatigue

The reduced release of Ca2+ from sarcoplasmic reticulum (SR) is considered a major determinant of muscle fatigue. In the present study, we investigated whether the presence of dantrolene, an established inhibitor of SR Ca2+ release, or caffeine, a drug facilitating SR Ca2+ release, modifies muscle fatigue development. Accordingly, the effects of Ca2+ release modulators were analyzed in vitro in mouse fast-twitch [extensor digitorum longus (EDL)] and slow-twitch (soleus) muscles, fatigued by repeated short tetani (40 Hz for 300 ms, 0.5 s-1 in soleus and 60 Hz for 300 ms, 0.3 s-1 in EDL, for 6 min). Caffeine produced a substantial increase of tetanic tension of both EDL and soleus muscles, whereas dantrolene decreased tetanic tension only in EDL muscle. In both EDL and soleus muscles, 5 μM dantrolene did not affect fatigue development, whereas 20 μM dantrolene produced a positive staircase during the first 3 min of stimulation in EDL muscle and a slowing of fatigue development in soleus muscle. The development of the positive staircase was abolished by the addition of 15 μM ML-7, a selective inhibitor of myosin light chain kinase. On the other hand, caffeine caused a larger and faster loss of tension in both EDL and soleus muscles. The results seem to indicate that the changes in fatigue profile induced by caffeine or dantrolene are mainly due to the changes in the initial tetanic tension caused by the drugs, with the resulting changes in the level of contraction-dependent factors of fatigue, rather than to changes in the SR Ca2+ release during fatigue development.

γ-Secretase Activity of Presenilin 1 Regulates Acetylcholine Muscarinic Receptor-mediated Signal Transduction

Familial Alzheimer's disease (FAD) presenilin 1 (PS1) mutations give enhanced calcium responses upon different stimuli, attenuated capacitative calcium entry, an increased sensitivity of cells to undergo apoptosis, and increased gamma-secretase activity. We previously showed that the FAD mutation causing an exon 9 deletion in PS1 results in enhanced basal phospholipase C (PLC) activity (Cedazo-Minguez, A., Popescu, B. O., Ankarcrona, M., Nishimura, T., and Cowburn, R. F. (2002) J. Biol. Chem. 277, 36646-36655). To further elucidate the mechanisms by which PS1 interferes with PLC-calcium signaling, we studied the effect of two other FAD PS1 mutants (M146V and L250S) and two dominant negative PS1 mutants (D257A and D385N) on basal and carbachol-stimulated phosphoinositide (PI) hydrolysis and intracellular calcium concentrations ([Ca2+]i) in SH-SY5Y neuroblastoma cells. We found a significant increase in basal PI hydrolysis in PS1 M146V cells but not in PS1 L250S cells. Both PS1 M146V and PS1 L250S cells showed a significant increase in carbachol-induced [Ca2+]i as compared with nontransfected or wild type PS1 transfected cells. The elevated carbachol-induced [Ca2+]i signals were reversed by the PLC inhibitor neomycin, the ryanodine receptor antagonist dantrolene, the general aspartyl protease inhibitor pepstatin A, and the specific gamma-secretase inhibitor N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester. The cells expressing either PS1 D257A or PS1 D385N had attenuated carbachol-stimulated PI hydrolysis and [Ca2+]i responses. In nontransfected or PS1 wild type transfected cells, N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester and pepstatin A also attenuated both carbachol-stimulated PI hydrolysis and [Ca2+]i responses to levels found in PS1 D257A or PS1 D385N dominant negative cells. Our findings suggest that PS1 can regulate PLC activity and that this function is gamma-secretase activity-dependent.

Ryanodine receptors in peritoneal mast cells: possible role in the modulation of exocytotic activity

Previous studies have shown that ryanodine in low concentrations and caffeine increase intracellular [Ca(2+)] in the absence of external Ca(2+), suggesting Ca(2+) release from intracellular stores through ryanodine receptors (RyR). In the present study we employed amperometry to examine the effect of RyR agonists and antagonists on serotonin release elicited with compound 48/80 (10 micro g/ml). Ryanodine (1 micro M) or, similarly, 20 mM caffeine, in the absence of external Ca(2+), enhanced the amperometric response to compound 48/80 and all the individual amperometric spike parameters. Ryanodine (50 micro M), dantrolene (20 micro M) and tetracaine (50 micro M), putative antagonists of the RyR, attenuated the amperometric response significantly, decreasing the number and frequency of events as well as their amplitude. This is the first demonstration that Ca(2+) availability from RyR-operated Ca(2+) sources may contribute to the modulation of secretory activity in mast cells, affecting not only the cellular exocytotic response, but also the characteristics of single amperometric events. Immunocytochemical labelling, using a monoclonal RyR antibody, confirmed the presence of RyR in this preparation.

Effects of alpha-scorpion toxin, tityustoxin on the release of [3H] dopamine of rat brain prefrontal cortical slices

The effect of tityustoxin (TsTX) on the release of [3H] dopamine in rat brain prefrontal cortical slices was investigated. The stimulatory effect of TsTX was dependent on incubation time and TsTX concentration with an EC50 of 0.05 microM. The release of [3H] dopamine stimulated by TsTX is dependent of Na+ channels and thus, was completely, inhibited by tetrodotoxin. Tityustoxin-induced release of [3H] dopamine was not blocked by ethylene glycol-bis(beta-aminoethyl) ether (EGTA) and thus was independent of extracellular calcium. However, [3H] dopamine release induced by TsTX was inhibited by 52% by BAPTA, a calcium chelator. Moreover, dantrolene (100 microM) and tetracaine (500 microM) partially inhibited by 38 and 29%, respectively, the tityustoxin-induced release of [3H] dopamine from prefrontal cortical slices suggesting a role from intracellular calcium increase. In conclusion, part of the TsTX-induced release [3H] dopamine may be due to an effect of the toxin on the reversal of the dopamine transporter (DAT), but the majority of the toxin stimulated release of [3H] dopamine involves the mobilization of intracellular calcium stores.

Characteristics and a functional implication of Ca 2+ -activated K + current in mouse aortic endothelial cells

We employed the patch-clamp technique to investigate a Ca(2+)-activated K(+) (K(Ca)) current in cultured mouse aortic endothelial cells (MAECs). In the whole-cell mode, an increase in cytosolic [Ca(2+)] ([Ca(2+)](i)) to 2 micro M activated an outwards current. The [K(+)](o)-dependent change of the reversal potentials agreed well with the predicted Nernstian relation, suggesting that it was a K(Ca) current. The Hill coefficient (4) and EC(50) (740 nM) were obtained from the current/[Ca(2+)](i) relationship. Iberiotoxin (50 nM) or apamin (200 nM) failed to inhibit the current, whereas TEA (10 mM) suppressed the current to 73.6+/-1.6% of control ( n=9). The intermediate-conductance, Ca(2+)-activated K(+) (IK(Ca)) channel blockers charybdotoxin (50 nM), clotrimazole (10 micro M) and econazole (10 micro M) inhibited the K(Ca) current to 10.5+/-1.3% ( n=6), 16.6+/-3.1% ( n=6), and 19.3+/-2.5% ( n=5) of control, respectively. The IK(Ca) channel openers chlorzoxazone, zoxazolamine and 1-ethyl-2-benz-imidazolinone and the Ca(2+)-activated Cl(-) channel blocker niflumic acid activated the K(Ca) current. In inside-out patches, the single-channel conductance was 17.7 pS in symmetrical K(+) solutions. RT-PCR analysis showed transcripts of the murine IK1 channel (mIK1) in MAECs. The IK(Ca) channel blockers inhibited the ATP-induced [Ca(2+)](i) increase in MAECs and the endothelium-dependent relaxation of mouse aortic rings. In addition, the IK(Ca) channel openers augmented ATP-induced [Ca(2+)](i) increase in MAECs and evoked endothelium-dependent relaxation of mouse aorta. These results suggest that an mIK1-like channel mediates the native IK(Ca) current in MAECs and may contribute to endothelium-dependent relaxation by modulating MAEC [Ca(2+)](i).

Behavioural effects of thieno and pyrazolo [2,1] benzothiazepine derivatives in mice

Behavioural studies were conducted in mice with a number of hetero[2,1]benzothiazepine derivatives, analogues of tianeptine. Previously published studies in mice have shown that some of these compounds were effective in the tetrabenazine and Porsolt tests. In the present study, four of the 15 compounds under study potentiated the actions of 5-hydroxytryptophan (5-HTP, 50 mg/kg i.p.), but no significant antagonism of the apomorphine (16 mg/kg s.c.)-induced hypothermia and potentiation of the amphetamine actions was found. Moreover, some of them inhibited the stereotyped behaviour and/or climbing behaviour of low doses of apomorphine and compound 2 was effective in the plus-maze test. These compounds also produced a slight inhibition of exploratory behaviour in the holeboard test. On the other hand, no significant muscle relaxant and anticonvulsant activities were observed at any dose employed. Together, these data suggest that some of the compounds under study combine the antidepressant effects with additional neuroleptic or anxiolytic activities in mice.

Prophylactic tolperisone for post-exercise muscle soreness causes reduced isometric force--a double-blind randomized crossover control study

The role of tolperisone hydrochloride, a centrally acting muscle relaxant in relieving painful muscle spasm is recently being discussed. The present study hypothesizes that the prophylactic use of tolperisone hydrochloride may effectively relieve post-exercise muscle soreness, based on the spasm theory of exercise pain. Twenty male volunteers, aged 25.2 +/- 0.82 years (mean +/- SEM) participated in 10 sessions in which they received oral treatment with placebo or the centrally acting muscle relaxant tolperisone hydrochloride (150 mg) three times daily for 8 days, in randomized crossover double-blind design. Time course assessments were made for pressure pain threshold, Likert's pain score (0-5), pain areas, range of abduction, isometric force, and electromyography (EMG) root mean square (RMS) during maximum voluntary isometric force on day 1 and 6, immediately after an eccentric exercise of first dorsal interosseous muscle, and 24 and 48 h after the exercise. Treatment with placebo or tolperisone hydrochloride was initiated immediately after the assessments on the first day baseline assessments. On the sixth day baseline investigations were repeated and then the subjects performed six bouts of standardized intense eccentric exercise of first dorsal interosseous muscle for provocation of post-exercise muscle soreness (PEMS). Perceived intensity of warmth, tiredness, soreness and pain during the exercise bouts were recorded on a 10 cm visual analogue pain scale. VAS scores and pressure pain thresholds did not differ between tolperisone and placebo treatment. All VAS scores increased during the exercise bouts 2, 3, 4, 5 and 6 as compared to bout 1. Increased pain scores and pain areas were reported immediately after, 24 and 48 h after exercise. Pressure pain thresholds were reduced at 24 and 48 h after the exercise in the exercised hand. Range of abduction of the index finger was reduced immediately after the exercise and was still reduced at 24 h as compared to the non-exercised hand. The EMG RMS amplitude was also reduced immediately after the exercise, but was increased at 24 and 48 h. Isometric force was reduced immediately after the exercise as compared to days 1, 6, and the 24 and 48 h post-exercise assessments with a greater reduction following the tolperisone hydrochloride treatment and the reduction was more in tolperisone group as compared to the placebo group. The results suggest, that the prophylactic intake of tolperisone hydrochloride provides no relief to pain in course of post-exercise muscle soreness but results in reduction in isometric force.

Effect of muscle relaxants on experimental jaw-muscle pain and jaw-stretch reflexes: a double-blind and placebo-controlled trial

A randomised, double-blind, placebo-controlled three-way cross-over study was performed to investigate the effect of two muscle relaxants (tolperisone hydrochloride and pridinol mesilate) on experimental jaw-muscle pain and jaw-stretch reflexes. Fifteen healthy men participated in three randomised sessions separated by at least 1 week. In each session 300 mg tolperisone, 8 mg pridinol mesilate or placebo was administered orally as a single dose. One hour after drug administration 0.3 ml hypertonic saline (5.8%) was injected into the right masseter to produce muscle pain. Subjects continuously rated their perceived pain intensity on an electronic 10-cm visual analogue scale (VAS). The pressure pain threshold (PPT) was measured and short-latency reflex responses were evoked in the pre-contracted (15% maximal voluntary contraction) masseter and temporalis muscles by a standardised stretch device (1 mm displacement, 10 ms ramp time) before (baseline), 1 h after medication (post-drug), during ongoing experimental muscle pain (pain-post-drug), and 15 min after pain had vanished (post-pain). Analysis of variance demonstrated significantly lower VAS peak pain scores (5.9 +/- 0.4 cm) after administration of tolperisone hydrochloride compared with pridinol mesilate (6.8 +/- 0.4 cm) and placebo (6.6 +/- 0.4 cm) (P=0.020). Administration of pridinol mesilate was associated with a significant decrease in PPTs compared with tolperisone hydrochloride and placebo (P=0.002) after medication, but not after experimental jaw-muscle pain. The normalised peak-to-peak amplitude of the stretch reflexes were not significantly influenced by the test medication (P=0.762), but were in all sessions significantly facilitated during ongoing experimental jaw-muscle pain (P=0.034). In conclusion, tolperisone hydrochloride provides a small, albeit significant reduction in the perceived intensity of experimental jaw-muscle pain whereas the present dose had no effect on the short-latency jaw-stretch reflex.

Malignant hyperthermia

Malignant hyperthermia (MH) is an uncommon, life-threatening, acute pharmacogenetic disorder of the skeletal muscle cell. It manifests in susceptible individuals as a hypermetabolic response on exposure to halogenated volatile anaesthetics and depolarizing muscle relaxants. There may also be a relationship between susceptibility to MH, heat stroke and exercise-induced rhabdomyolysis. The pathophysiology of the crisis involves an uncontrolled release of cytoplasmic free calcium from the sarcoplasmic reticulum leading to activation of energy-producing biochemical pathways. Organ system failure and rhabdomyolysis may occur as a result of high fever, hyperkalaemia and acidosis. The ryanodine receptor, the calcium-release channel of the sarcoplasmic reticulum, is the primary locus for malignant hypothermia susceptibility. Multiple mutations in the gene for the ryanodine receptor protein are causative. Other genes may also be involved. A classical fulminant crisis presents with a rising end-tidal carbon dioxide, skeletal muscle rigidity, tachycardia, hyperthermia and acidosis. Mortality may be as high as 70% if the syndrome is not recognized and treated. Immediate discontinuation of triggering agents, oxygenation, and correction of acidosis and electrolyte abnormalities, cooling and dantrolene are essential for treatment of the syndrome. Thanks to clinical and research investigations, widespread education and the introduction of dantrolene sodium, the mortality from MH is less than 5%. This chapter provides an overview and an update of MH.

Induction of Malignant Hyperthermia in Susceptible Swine by 3,4-Methylenedioxymethamphetamine (“Ecstasy”)

Background

3,4-Methylenedioxymethamphetamine (MDMA, "ecstasy") can mediate acute toxic effects such as muscle rigidity, metabolic acidosis, and hyperthermia. Because of close clinical similarities, an association between MDMA intoxication and malignant hyperthermia (MH) was suggested. The aim of this study was to investigate whether MDMA is a trigger of MH in susceptible swine.

Methods

MH-nontriggering general anesthesia was performed in six MH-susceptible (MHS) and six MH-normal swine. The animals were exposed to MDMA in cumulative doses of 0.5, 1, 2, 4, 8, and 12 mg/kg. The clinical occurrence of MH was defined by achievement of two of three conditions: central venous Pco2 >/=75 mmHg, central venous pH </= 7.20, and increase of body core temperature >/= 2.0 degrees C. Once MH occurred, a standardized therapy with dantrolene, sodium bicarbonate, and hyperventilation with 100% oxygen was initialized.

Results

Administration of 8 mg/kg MDMA triggered MH in all MHS swine. The MH-normal swine also developed clinical signs of hypermetabolism, but even after administration of 12 mg/kg MDMA, changes were moderate compared with the MHS swine. Dantrolene therapy of MDMA-induced MH crisis in the MHS swine partially counteracted the clinical signs of MH immediately.

Conclusions

MDMA induces MH in genetically susceptible swine in relevant doses. Therefore, MHS patients should avoid use of MDMA or related drugs. Patients with a personal or family history of MDMA-induced hyperthermia should be tested for a diagnosis of MH susceptibility. Dantrolene is effective in therapy of MDMA-induced porcine MH.

Effects of gustatory nerve transection and regeneration on quinine-stimulated Fos-like immunoreactivity in the parabrachial nucleus of the rat

The distribution of quinine-stimulated Fos-like immunoreactivity (FLI) in several subdivisions of the parabrachial nucleus (PBN) known to be responsive to gustatory stimulation was examined in rats in which the chorda tympani nerve (CT) and/or glossopharyngeal nerve (GL) was transected (Experiment 1) and in rats in which the GL was transected with regeneration promoted or prevented (Experiment 2). We confirmed previous findings in the literature by demonstrating that rats intraorally infused with 3 mM quinine showed a robust population of FLI in the waist area and the external lateral (EL) and external medial (EM) subdivisions of the PBN (Yamamoto et al. [1994] Physiol Behav 56:1197-1202; Travers et al., [ 1999] Am J Physiol 277:R384-R394). In the waist area, only GL transection significantly decreased the number of FLI-neurons elicited by intraoral infusion of quinine compared with water-stimulated controls. In the external subdivisions neither neurotomy affected the number of FLI-neurons. The effect of GL transection in the waist area was enduring for rats in which the GL did not regenerate (up to 94 days), but regeneration of the GL after 52 days restored quinine-stimulated FLI to control values. In these same GL-transected animals, there were parallel decreases in the number of gapes elicited by intraoral quinine stimulation that recovered, but only subsequent to regeneration of the GL. These data provide support for the role of the waist area in the brainstem processing that underlies oromotor rejection behaviors and also help substantiate the hypothesis that the CT and GL are relatively specialized with regard to function. Moreover, when the quinine-induced pattern of neural activity in the second central gustatory relay, as assessed by FLI, is substantially altered by the loss of peripheral gustatory input from the GL, it can be restored upon regeneration of the nerve.

In vitro effects of dantrolene sodium and verapamil on noradrenaline-induced contractions of rabbit aorta and their interactions

The effects of dantrolene sodium (0.1 to 10 microM) and verapamil (0.01 to 1 microM) administered alone or together (1 microM verapamil, 0.1 to 10 microM dantrolene sodium) were investigated in isolated rabbit thoracic aorta precontracted with 0.1 microM noradrenaline (NA). Verapamil plus dantrolene sodium produced a dose-dependent inhibition of aortic strips contractions evoked by NA, and all concentrations of dantrolene sodium significantly decreased the inhibitory effect of 1 microM verapamil (p < 0.001, ANOVA). In conclusion, dantrolene sodium and verapamil inhibited 0.1 microM noradrenaline-evoked aorta contractions, and all doses of dantrolene sodium decreased the inhibitory effect of 1 microM verapamil in a dose-dependent manner.

Time course of the effect of a bolus dose of intrathecal baclofen on severe cerebral spasticity

Continuous intrathecal administration of baclofen with implanted programmable pump systems is recommended in the treatment of severe spasticity of cerebral origin. Prior to pump implantation, a baclofen bolus test (BBT) is used to assess the effectiveness of intrathecal baclofen using clinical scales such as the Modified Ashworth Scale (MAS). In the literature, the time and period of maximum effect of a bolus dose of intrathecally administered baclofen in patients with cerebral spasticity is variously reported. The aim of the study was, therefore, to reveal the time course of the effect of a BBT on severe cerebral spasticity by the use of a recently described spasticity measurement method. Spasticity in knee joints of 13 patients with severe cerebral spasticity was repeatedly assessed using the MAS and also continuously recorded by the measurement of force under circular fibreglass casts. Force was recorded as nettorque by multiplying the force by the distance between sensor and joint axis, thus allowing inter-individual comparison. Half-hour time integrals (TI) of net-torque were determined 9 hours before and 22 hours after intrathecal baclofen administration. Post-BBT half-hour time integrals (TI(+0), TI(+0.5), to TI(+22)) were compared with the mean of 17 pre-BBT half-hour time integrals. Significantly lower post-BBT half-hour time integrals compared with were found between TI(+2) and TI(+8) (Dunnett adjusted p < 0.05). The median lowest TI after BBT of the 13 patients was TI(+4). The lowest mean MAS scores were found 4 hours after BBT. The findings suggest that the greatest effect of BBT on cerebral spasticity occurs between 2 and 8.5 hours, with a maximal effect at 4 hours after intrathecal baclofen injection. Clinical scales used to determine the effect of BBT should thus be carried out during this period-ideally at 4 hours after baclofen injection.

Sevoflurane inhibits guanosine 5'-[gamma-thio]triphosphate-stimulated, Rho/Rho-kinase-mediated contraction of isolated rat aortic smooth muscle

BACKGROUND

The Rho/Rho-kinase signaling pathway plays an important role in mediating Ca2+ sensitization of vascular smooth muscle. The effect of anesthetics on Rho/Rho-kinase-mediated vasoconstriction has not been determined to date. This study is designed to examine the possible inhibitory effects of sevoflurane on the Rho/Rho-kinase pathway by measuring guanosine 5'-[gamma-thio]triphosphate (GTP gamma S)-stimulated contraction and translocation of RhoA (one of the three Rho subtypes) and Rock-2 (one of the two Rho-kinase subtypes) from the cytosol to the membrane in rat aortic smooth muscle.

METHODS

GTP gamma S-induced contraction of rat aortic endothelium-denuded rings was measured using an isometric force transducer, and GTP gamma S-stimulated membrane translocation of RhoA and Rock-2 in smooth muscle cells was detected with Western blotting in the presence and absence of sevoflurane.

RESULTS

GTP gamma S (10(-4) m) induced a sustained contraction, which was significantly inhibited by the Rho-kinase inhibitor, Y27632 (3 x 10(-6) m). Before treatment with GTP gamma S, RhoA and Rock-2 were detected primarily in the cytosolic fraction. GTP gamma S (10(-4) m) stimulated the translocation of RhoA and Rock-2 from the cytosol to the membrane, which was sustained for more than 60 min. Sevoflurane (1.7, 3.4, and 5.1%) concentration dependently inhibited the GTP gamma S-induced constriction of rat aortic smooth muscle with a reduction of constriction of 52-75% (P < 0.01, n = 8), and attenuated the translocation of RhoA and Rock-2 by 31-66% and 34-78%, respectively (P < 0.05-0.01, respectively; n = 4).

CONCLUSION

The current findings show that sevoflurane depresses the GTP gamma S-stimulated contraction and translocation of both Rho and Rho-kinase from the cytosol in a concentration-dependent manner, indicating that sevoflurane is able to inhibit vasoconstriction mediated by the Rho/Rho-kinase pathway in rat aortic smooth muscle.

Erectile physiological and pathophysiological pathways involved in erectile dysfunction

PURPOSE

The importance of signaling pathways in penile smooth muscles involved in normal erection and erectile dysfunction (ED) is discussed based on a review of the literature.

MATERIALS AND METHODS

Erection is basically a spinal reflex that can be initiated by recruitment of penile afferents but also by visual, olfactory and imaginary stimuli. The generated nervous signals will influence the balance between the contractant and relaxant factors, which control the degree of contraction of penile smooth muscles and, thus, determine the functional state of the penis. The different steps involved in neurotransmission, impulse propagation and intracellular transduction of neural signals may be changed in different types of erectile dysfunction.

RESULTS

Recent findings have suggested an important role for RhoA/Rho kinase in the regulation of cavernosal smooth muscle tone and that changes in this pathway may contribute to ED in various patient subgroups, eg diabetes and vascular disease. Neurogenic nitric oxide is still considered the most important factor for immediate relaxation of penile vessels and corpus cavernosum. However, endothelially generated nitric oxide seems essential for maintaining erection. Endothelial dysfunction can contribute to ED in several patient subgroups. In addition, in conditions associated with reduced function of nerves and endothelium, such as aging, hypertension, smoking, hypercholesterolemia and diabetes, circulatory and structural changes in the penile tissues can result in arterial insufficiency and defect muscle relaxation.

CONCLUSIONS

Different types of ED often have overlapping pathophysiologies but may also have common pathways contributing to ED. Such pathways may be potential treatment targets.

Differential effects of baclofen on lower oesophageal sphincter pressure and proximal gastric motility in humans

BACKGROUND

The gamma-aminobutyric acid receptor type B agonist, baclofen, inhibits transient lower oesophageal sphincter relaxations by influencing a vagal pathway. Although post-prandial proximal gastric function, which is vagally mediated, is important in the occurrence of transient lower oesophageal sphincter relaxations, the effects of baclofen on post-prandial proximal gastric motility in humans remains undetermined.

AIM

To determine the effects of baclofen on post-prandial lower oesophageal sphincter function and proximal gastric motility in healthy subjects.

METHODS

In 11 healthy volunteers, a barostat bag and an oesophageal manometric catheter with a sleeve were simultaneously positioned; 40 mg of oral baclofen or placebo was then given in a randomized, double-blind manner. Subsequently, the intragastric bag volume, oesophageal and lower oesophageal sphincter pressure and oesophageal pH were recorded during the 90 min before and 120 min after a meal.

RESULTS

During the post-prandial period, unlike the fasting period, baclofen decreased the rate of transient lower oesophageal sphincter relaxations and increased the basal lower oesophageal sphincter pressure compared with placebo. However, the meal-induced decrease in the tone and phasic contractility of the fundus was not affected by baclofen.

CONCLUSION

The gamma-aminobutyric acid receptor type B agonist, baclofen, has a potent effect on post-prandial lower oesophageal sphincter motility without altering post-prandial proximal gastric motility, suggesting differential effects of baclofen on different signals of gastrointestinal vagal afferents.

Intrathecal baclofen in subjects with spastic hemiplegia: assessment of the antispastic effect during gait

OBJECTIVE

To determine whether leg muscle stiffness is measurably reduced after intrathecal baclofen (ITB) in subjects with spastic hemiplegia.

DESIGN

Nonrandomized trial.

SETTING

Inpatient multidisciplinary rehabilitation unit in France.

PARTICIPANTS

Seven consecutive subjects with spastic hemiplegia having Ashworth Scale scores for their quadriceps and triceps greater than 2.

INTERVENTION

Subjects were given ITB by lumbar puncture after a dose-selecting test period.

MAIN OUTCOME MEASURES

Triceps and quadriceps Ashworth scores, gait analysis at preferred and maximal speed measured by a motion analysis system with 2 forceplates, and electromyographic recording of leg muscles before and 4 hours after ITB. The slopes of the moment-angle curves were measured on the hemiplegic side at the onset of ankle and knee flexion to assess muscle stiffness during walking. Pre- and post-ITB spatiotemporal, kinetic, and kinematic data were compared by using a nonparametric test (Wilcoxon signed-rank test).

RESULTS

Ashworth scores of the quadriceps and triceps of all subjects decreased significantly after ITB. Maximal walking speed increased significantly, with a significant increase in stride length, but the preferred walking speed was unchanged. Minimal knee extension and maximal ankle flexion were the only kinematic data significantly different (increased) after ITB. The slope of the ankle moment-angle curve decreased significantly after ITB at preferred gait speed; it also decreased at maximal gait speed in all but 1 subject. Of the 4 available moment-angle curves, 3 showed decreased knee extensor muscle stiffness. The duration of the bursts of spastic muscles decreased after ITB.

CONCLUSION

Acute ITB improved walking and reduced muscle stiffness at both the ankles and knees on the spastic hemiplegic side of our subjects. Electromyographic findings suggest that some of the post-ITB reduction in muscle stiffness might be attributed to decreased spasticity.

Hemodynamic interactions of propofol and dantrolene in chronically instrumented dogs

The hemodynamic interaction of dantrolene, a specific drug for malignant hyperthermia, and propofol which appears to be safe in malignant hyperthermia-susceptible patients, has not been investigated. We performed this study to examine the hemodynamic actions of dantrolene at a therapeutic dose during propofol anesthesia. Ten dogs were chronically instrumented for the measurements of systemic and coronary hemodynamics. The dogs were assigned to receive propofol with vehicle or dantrolene in a random manner on separate experimental days. Propofol significantly decreased mean arterial blood pressure, left ventricular systolic and end-diastolic pressure, the maximal rate of increase in left ventricular pressure, and left ventricular regional segment shortening. Coronary blood flow (CBF) was unchanged but coronary vascular resistance (CVR) decreased. Dantrolene reversed the decrease in mean arterial blood pressure and left ventricular systolic pressure caused by propofol, and significantly increased heart rate. However, left ventricular end-diastolic pressure, cardiac output, maximal rate of increase in left ventricular pressure, and segment shortening were unchanged. CBF was significantly increased with a decrease in CVR. These results suggest that dantrolene reverses the hypotensive action produced by propofol and causes an increase in CBF with a decrease in CVR, but does not significantly change the negative inotropic effects. Thus, dantrolene exerts favorable hemodynamic effects during propofol anesthesia.

IMPLICATIONS

Our study suggests that dantrolene reverses the hypotensive action produced by propofol and causes an increase in coronary blood flow with a decrease in coronary vascular resistance, but does not significantly change the negative inotropic effects.

Anticonvulsant, sedative and muscle relaxant effects of carbenoxolone in mice

BACKGROUND

Carbenoxolone, as an antiulcer medicine, has some pharmacological properties such as: the inhibition of gap junctional (GJ) intercellular communication. In vitro studies have shown, carbenoxolone to abolish the generation of full or partial ectopic spike generation, by 4-aminopyridine, as well as spontaneous epileptiform activity in CA3 or CA1 regions of the rat hippocampal slices via closing GJ channels. Thus, we considered the possible anticonvulsant effects of carbenoxolone in animal seizure models.

RESULTS

ED50 values of diazepam and carbenoxolone in the pentylenetetrazole model were 1.13 mg/kg and 283.3 mg/kg, respectively. In this model, carbenoxolone in doses of 200 and 300 mg/kg prolonged the onset time of seizure and decreased the duration of seizures. In the maximal electroshock model, carbenoxolone in a dose of 400 mg/kg decreased the duration of seizure producing protection against seizure but failing to protect against mortality in comparison with diazepam. In the potentiation of pentobarbitone sleep test, carbenoxolone significantly increased sleeping time and decreased latency in doses of 100, 200 and 300 mg/kg in mice dose dependently. In the traction test, carbenoxolone (400 mg/kg) showed muscle relaxant activity and in the accelerated rotarod test, carbenoxolone in doses of 200 and 300 mg/kg showed a decline in motor coordination.

CONCLUSION

It can be concluded that carbenoxolone possesses anticonvulsant, muscle relaxant and hypnotic effects, which could contribute to the control of petit mal and grand mal seizures.

The role of the presenilin-1 homologue gene sel-12 of Caenorhabditis elegans in apoptotic activities

Many cases of autosomal dominant early onset familial Alzheimer's disease result from mutations in presenilin-1 (PS1). In this study, we examined the role of the PS1 homologue gene sel-12 of Caenorhabditis elegans under oxidative stress and clarified the sel-12-induced apoptosis. A genetic null allele mutant, sel-12(ar171), showed resistance to oxidative stress and prevented mitochondrial dysfunction-induced apoptosis. On the other hand, another allele mutant, sel-12(ar131), that carries a missense mutation showed a proapoptotic activity, which may be the result of a gain of function property. Also, sel-12(ar131)-induced apoptosis was ced-3- and ced-4-dependent. Dantrolene, which specifically inhibits Ca(2+) release from endoplasmic reticulum stores, prevents sel-12(ar131)-induced apoptosis. SEL-12, which is localized in the endoplasmic reticulum, may induce apoptosis through abnormal calcium release from the endoplasmic reticulum. Together, with the previous finding that human PS1 could substitute for SEL-12, these results suggest the similar involvement of PS1-inducing apoptosis under oxidative stress and mitochondrial dysfunction in the Alzheimer's Disease brain.

Increased relaxant action of forskolin and isoproterenol against muscarinic agonist-induced contractions in smooth muscle from M2 receptor knockout mice

The ability of forskolin and isoproterenol to inhibit the contractile action of the muscarinic agonist, oxotremorine-M, was investigated in smooth muscle from wild-type and M(2) muscarinic receptor knockout mice. Forskolin (5.0 micro M) caused a significant reduction in the contractile activity of oxotremorine-M in ileum, trachea, and urinary bladder from both wild-type and M(2) muscarinic receptor knockout mice. This reduction in contractile activity was characterized by decreases in potency or maximal response, but not always both. Similar results were obtained with isoproterenol (1.0 micro M). The relaxant effects of forskolin in ileum, trachea, and urinary bladder from M(2) receptor knockout mice were approximately 3- to 9-fold greater than those observed in the same tissues from wild-type mice. Similar results were obtained with isoproterenol in ileum and urinary bladder, although the differences between wild-type and M(2) receptor knockout tissues were less than those observed with forskolin. In contrast, there was no significant difference between the relaxant effect of isoproterenol in trachea from wild-type and M(2) receptor knockout mice. In contrast to the results observed with oxotremorine-M as the contractile agent, forskolin and isoproterenol did not exhibit greater relaxant activity against KCl-induced contractions in M(2) receptor knockout mice compared with wild-type mice. These results suggest that a component of the contractile response to muscarinic agonists in smooth muscle involves an M(2) muscarinic receptor-mediated inhibition of the relaxant effects of agents that increase cAMP levels.

Psychopharmacological effects of tianeptine analogous hetero[2,1] benzothiazepine derivatives

The psychopharmacological effects of a number of thieno and pyrazolo[2,1] benzothiazepine derivatives as well as several synthetic intermediate compounds were investigated in mice. Previously published studies in mice have shown that some of these compounds were effective in the tetrabenazine and Porsolt tests. In the present study, 7 of the 15 compounds under study clearly antagonized the apomorphine (16 mg/kg s.c.)-induced hypothermia, but no significant potentiation of the 5-hydroxytryptophan (5-HTP) and amphetamine actions was found. Five of them inhibited the syndrome induced by 5-HTP (250 mg/kg i.p.). Moreover, some of them were effective in the plus-maze test and antagonized the apomorphine (3 mg/kg s.c.)-induced effects. On the other hand, these compounds produced a moderate inhibition of exploratory behaviour in the hole-board test, but they had no significant muscle relaxant and anticonvulsant activities. The results indicate that some of the compounds under study combine a spectrum of antidepressant, anxiolytic and neuroleptic properties in mice with a lack of muscle relaxant and anticonvulsant activities.

Dantrolene analogues revisited: general synthesis and specific functions capable of discriminating two kinds of Ca2+ release from sarcoplasmic reticulum of mouse skeletal muscle

The general synthesis of dantrolene analogues with various substituents on its phenyl ring has been developed via palladium-catalyzed cross-coupling reactions, the Stille or Suzuki reaction, as the key step. The effects of synthesized analogues have been evaluated by two kinds of Ca(2+) release modes from sarcoplasmic reticulum (SR) of mouse skeletal muscle fibers based on: (1) the measurement of twitch contraction caused by the physiological Ca(2+) release (PCR) of intact skeletal muscle and (2) the rate of Ca(2+)-induced Ca(2+) release (CICR) in saponin-treated skinned muscle fibers. Although dantrolene, a lead compound, inhibits both twitch contraction and CICR, some structurally modified analogues exhibit one or the other of these effects. The methoxy congener, GIF-0185, potently inhibits the twitch contraction without affecting the CICR, while GIF-0166 and GIF-0248, the ortho-nitro regioisomer and ortho, ortho-dinitro substituted analogues, respectively, doubly potentiate the CICR exclusively.

Cellular mechanisms of the acute increase of glutamate release induced by nerve growth factor in rat cerebral cortex

Nerve growth factor (NGF) was found to increase glutamate release in the developing visual cortex. We investigated the cellular mechanisms of this effect and its dependence on extracellular and intracellular Ca2+. The NGF-induced enhancement of glutamate release from superfused rat visual cortex synaptosomes required mild depolarization. Removal of external Ca2+ during depolarization with 15 mM K+ only halved the effect of NGF on glutamate release. NGF increased [Ca2+]i in K+-depolarized synaptosomes preloaded with fura-2AM both in the presence and in the absence of external Ca2+. The effects of NGF on glutamate release and [Ca2+]i elevation were prevented by an anti-TrkA receptor monoclonal antibody. NGF increased synaptosomal inositol (1,4,5)-triphosphate (InsP3) during depolarization and the InsP3 receptor antagonist heparin abolished the effect of NGF on evoked glutamate release both in the presence and in the absence of external Ca2+. The effect of NGF on the evoked glutamate release in Ca2+-free medium was abolished by dantrolene, a ryanodine receptor blocker, by CGP 37157, a blocker of the mitochondrial Na+/Ca2+ exchanger and by pretreatment of synaptosomes with caffeine. NGF significantly increased the depolarization-induced activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and the subsequent phosphorylation of synapsin I in the absence of external Ca2+ and the NGF effect on evoked glutamate release was inhibited by the CaMKII inhibitors KN-93 and CaMKII 281-309 peptide but not by the MAP kinase inhibitor PD 98059. Thus, the effect of NGF on evoked glutamate release is linked to an increase in [Ca2+]i contributed by both Ca2+ entry and mobilization from InsP3-sensitive, ryanodine-sensitive and mitochondrial stores and to the subsequent activation of CaMKII.

[Dantrolene. Pharmacological and therapeutic aspects]

Malignant hyperthermia (MH) is a genetic, potentially life-threatening disorder of the skeletal muscle presenting during or following general anaesthesia. Trigger agents are volatile anaesthetics and depolarising muscle relaxants. Dantrolene is the only available drug for effective and specific MH therapy, which reduces significantly the mortality rate. Dantrolene is a skeletal muscle relaxant that depresses the excitation-contraction coupling,however, the specificity of action remains unknown. Recent studies identified the ryanodine receptor, the calcium release channel of the sarcoplasmic reticulum, as the direct molecular target of dantrolene. In addition to its use for MH, dantrolene is used in other disorders such as neuroleptic malignant syndrome and spasticity. Since dantrolene is weakly water soluble, the clinical preparation is time and manpower consuming. New agents have been synthesized, but because of economic considerations no registration for clinical usage has been realised.

Incremental responses of compound muscle action potentials in normal rats produced by repeated electrical stimulation

The purpose was to clarify the mechanism of normal incremental amplitude responses in compound muscle action potentials (CMAPs) and single fiber action potentials (SFAPs) produced by repeated high frequency electrical stimulation. Whereas the amplitude response of CMAPs and SFAPs increased during stimulation at 20 c.p.s. of the right flexor carpi ulnaris muscles of 50 rats, their durations gradually decreased. Incremental responses of the CMAPs and SFAPs evoked by repeated stimulation were suppressed in 25 rats by 30 mg/kg of magnesium sulfate and in 25 rats by 120 mg/kg of dantrolene sodium. We speculate that the incremental responses of CMAPs and SFAPs evoked by repeated stimulation were suppressed by the unchanged shape of the muscle after the injection of those chemicals.

Does monitoring of post-tetanic count prevent alarms of airway pressure or visible muscle activity during intratracheal jet ventilation? A prospective study with five different neuromuscular blocking agents

OBJECTIVE

Profound neuromuscular block (NMB) quantified by post-tetanic count (PTC) may prevent all muscle activity during anesthesia. We studied whether monitoring of PTC prevents airway pressure alarms or visible movements of the vocal cords and the abdomen during endolaryngeal procedures (ELPs).

METHODS

In this prospective, double blind, study 50 healthy (ASA 1-3) patients scheduled for ELPs were randomized into five groups: atracurium, mivacurium, rocuronium, vecuronium and succinylcholine. During alfentanil-propofol anaesthesia, profound NMB was controlled by monitoring the PTC (target level PTC 0-2, 50 Hz tetanic stimulation) of the adductor pollicis muscle. The muscle relaxants were administered using bolus dosing in all groups but in the succinylcholine group. The early signs of recovery of NMB to be observed were: 1) airway pressure alarms, 2) movements of vocal cords on the laryngeal video monitor and 3) movements of the abdomen. The inference was based on 90% confidence interval tests.

RESULTS

During 50 ELP:s following signs of early recovery of NMB were recognized: 2 alarms of airway pressure, 16 laryngeal movements and 11 movements of the abdomen. The proportion of airway pressure alarms was significantly lower than proportion of all detectable movements (95% confidence interval analysis). Twelve of the movements were recorded at PTC zero level. The signs of early recovery of NMB were detected in all groups.

CONCLUSIONS

PTC-monitoring following 50 Hz stimulation does not ensure total inactivity of muscles during alfentanil-propofol anesthesia, regardless which relaxant has been chosen. During ELPs, simultaneous observation of the vocal cords and the abdomen is more sensitive in detecting early recovery of NMB compared to our method of airway pressure monitoring.

Muscle relaxant activity of Elaeagnus angustifolia L. fruit seeds in mice

Muscle relaxant effect of Elaeagnus angustifolia L. (Elaeagnaceae) fruit seeds was studied in mice using traction test. The aqueous and ethanolic extracts (i.p) induced a muscle relaxant effect in a dose dependent manner as effective as diazepam (1 mg/kg). The aqueous extract was partitioned with methanol-chloroform (MeCh) and n-butanol (Bu.) saturated with water. The MeCh and Bu. fractions did not show activity. Preliminary phytochemical tests showed that the extract contains flavonoid. The results suggested that E. angustifolia fruit seeds exerted muscle relaxant activity via flavonoid component(s).

Indanylidenes. 2. Design and synthesis of (E)-2-(4-chloro-6-fluoro-1-indanylidene)-N-methylacetamide, a potent antiinflammatory and analgesic agent without centrally acting muscle relaxant activity

Extension of the structure-activity relationship studies that led to the discovery of the nonsedating potent muscle relaxant, antiinflammatory, and analgesic agent (E)-2-(4,6-difluoro-1-indanylidene)acetamide, 1, has given rise to (E)-2-(4-chloro-6-fluoro-1-indanylidene)-N-methylacetamide, 2. Compound 2 is a potent antiinflammatory and analgesic agent without centrally acting muscle relaxant activity.

Indanylidenes. 1. Design and synthesis of (E)-2-(4,6-difluoro-1-indanylidene)acetamide, a potent, centrally acting muscle relaxant with antiinflammatory and analgesic activity

The design of rigid cyclic analogues derived from cinnamamide 1, (E)-N-cyclopropyl-3-(3-fluorophenyl)prop-2-enamide, and beta-methylcinnamamide 2, (E)-N-cyclopropyl-3-(3-fluorophenyl)but-2-enamide, has led to the discovery of the potent, centrally acting muscle relaxant (E)-2-(4,6-difluoro-1-indanylidene)acetamide, 17. Compound 17 also possesses potent antiinflammatory and analgesic activity. This paper describes the synthesis and the muscle relaxant, antiinflammatory, and analgesic structure-activity relationships of 17 and 67 of its analogues. Compound 17 has been taken into phase I clinical trials.

Synthesis and benzodiazepine receptor affinity of pyrazolo[1,5-a]pyrimidine derivatives. 3. New 6-(3-thienyl) series as alpha 1 selective ligands

New 3-aryl-6-(3-thienyl)pyrazolo[1,5-a]pyrimidin-7-ones (2a-j) are synthesized and evaluated in vitro on Bz/GABA(A) receptors and on recombinant benzodiazepine receptors (alpha x beta 2/3 gamma 2; x = 1-3, 5) expressed in HEK293 cells. SAR studies on the new compounds are conducted and molecular modeling is accomplished to better investigate requirements leading to subtype selectivity. Some of the synthesized compounds are tested in vivo to explore their pharmacological effect as a consequence of their high alpha 1 beta 2 gamma 2 subtype selectivity observed in vitro.

Stimulatory effects of chlorzoxazone, a centrally acting muscle relaxant, on large conductance calcium-activated potassium channels in pituitary GH3 cells

Chlorzoxazone, a centrally acting muscle relaxant, has been used as a marker for hepatic CYP2E1 activity. However, little is known about the mechanism of chlorzoxazone actions on ion currents in neurons or neuroendocrine cells. We thus investigated its effects on ion currents in GH(3) lactotrophs. Chlorzoxazone reversibly increased Ca(2+)-activated K(+) current (I(K(Ca))) in a concentration-dependent manner with an EC(50) value of 30 microM. The chlorzoxazone-stimulated I(K(Ca)) was inhibited by iberitoxin (200 nM) or clotrimazole (10 microM), but not by glibenclamide (10 microM) or apamin (200 nM). Chlorzoxazone (30 microM) suppressed voltage-dependent L-type Ca(2+) current. In the inside-out configuration, chlorzoxazone applied to the intracellular side of the patch did not modify single-channel conductance of large conductance Ca(2+)-activated K(+) (BK(Ca)) channels, but did increase channel activity by increasing mean open time and decreasing mean closed time. Chlorzoxazone also caused a left shift in the activation curve of BK(Ca) channels. However, Ca(2+)-sensitivity of these channels was unaffected by chlorzoxazone. 1-Ethyl-2-benzimidazolinone (30 microM), 2-amino-5-chlorobenzoxazole (30 microM) or chlormezanone (30 microM) enhanced BK(Ca) channel activity, while 6-hydroxychlorzoxazone (30 microM) slightly increased it; however, chlorphenesin carbamate (30 microM) had no effect on it. Under the current-clamp condition, chlorzoxazone (10 microM) reduced the firing rate of action potentials. In neuroblastoma IMR-32 cells, chlorzoxazone (30 microM) also stimulated BK(Ca) channel activity. The stimulatory effects of chlorzoxazone on these channels may be responsible for the underlying mechanism of chlorzoxazone actions on neurons and neuroendocrine cells.

Effects of cholecystokinin tetrapeptide (CCK(4)) and of anxiolytic drugs on GABA outflow from the cerebral cortex of freely moving rats

The effect of cholecystokinin tetrapeptide (CCK(4)) and of different anxiolytic drugs on GABA outflow from the cerebral cortex was investigated in freely moving rats, by using the epidural cup technique. CCK(4) (3-30 microg/kg, i.p.) increased GABA outflow and induced objective signs of anxiety. These neurochemical and behavioral responses were prevented by the CCK(B) antagonist GV150013 at 0.1 microg/kg (i.p.). At higher doses (up to 30 microg/kg) this compound per se reduced GABA release and caused sedation, suggesting the presence of a CCKergic positive tonic modulation on GABA interneurons. Similarly the GABA(A) receptors modulator, diazepam (2mg/kg, i.p.) and the 5-HT(1A) agonist buspirone (3mg/kg, i.p.) reduced GABA outflow and caused the expected behavioral effects (reduced muscle tone, mild 5-HT syndrome) which were prevented by the respective, selective antagonists, flumazenil (1mg/kg, i.p.) and NAN-190 (3mg/kg, i.p.). These findings support the idea that GV150013, diazepam and buspirone inhibit GABAergic cortical activity, through the respective receptors. This neurochemical effect may represent the end-effect of various anxiolytic compounds affecting the cortical circuitry.

Quinine inhibits vascular contraction independent of effects on calcium or myosin phosphorylation

This report contains results of studies designed to determine whether quinine has direct effects on myofilament Ca2+ sensitization in addition to effects on Ca2+. Quinine decreased the EC50 value and maximal contraction of intact arterial strips to histamine. Incubation of arterial strips with indomethacin or 1H-[1,2,4]oxadiazole[4,3-alpha]quinoxalin-1-one did not alter quinine inhibition, suggesting that the effect is not mediated via cyclooxygenase or cGMP. Pretreatment of strips with quinine had no effect on the histamine-dependent increases in myosin light chain phosphorylation levels. Quinine inhibited Ca2+-induced contraction in alpha-toxin permeabilized strips, but not the Ca2+-induced contraction in Triton X-100 permeabilized strips. Pretreatment of the alpha-toxin permeabilized strips with quinine before stimulation with guanosine-5'-O-(3-thio)triphosphate (GTPgammaS) did not have any effect on the response. In conclusion, quinine inhibited Ca2+-dependent contractions of the alpha-toxin permeabilized strips, which retain modulatory pathways both upstream and downstream from the contractile proteins but did not inhibit GTPgammaS-dependent contraction of the alpha-toxin permeabilized preparation important in upstream modulation of the contraction. Moreover, quinine did not inhibit the Ca2+-dependent contractions of the Triton X-100 permeabilized strips, which are devoid of all modulatory pathways. This suggests that quinine does not act upstream from or directly on the contractile proteins. A more likely site of action may be downstream of the contractile proteins and specifically at the coupling of the contractile proteins with the physiological endpoint of force development.

FK506 attenuates 1-methyl-4-phenylpyridinium- and 3-nitropropionic acid-evoked inhibition of kynurenic acid synthesis in rat cortical slices

Kynurenic acid (KYNA), the only known endogenous glutamate antagonist, is produced in the brain by kynurenine aminotransferases (KATs) I and II. Mitochondrial toxins, 1-methyl-4-phenylpyridinium (MPP +) and 3-nitropropionic acid (3-NPA), were previously shown to reduce KYNA synthesis via interference with KAT I and II. Data presented here demonstrate that immunophilin ligand, FK506 (10-130 microM), but not CsA (1-50 microM), or ryanodine receptor blocker, dantrolene (1-100 microM), enhances the formation of KYNA in cortical slices. FK506, but not CsA or dantrolene, abolished the inhibition of KYNA synthesis evoked by MPP+ and 3-NPA. None of studied compounds influenced the activity of KAT I and KAT II. FK506 is the first among currently used drugs that might stimulate KYNA synthesis. This effect does not seem to arise from the interference with KATs or calcineurin activity.

Diazepam as an adjuvant analgesic to morphine for pain due to skeletal muscle spasm

Side effects of morphine are common when it is given in titrated doses to control severe pain in advanced cancer. We describe a case of severe back pain resistant to parenteral morphine accompanied by muscle spasm, in which the addition of diazepam both had an opioid-sparing effect and provided superior symptomatic relief. Diazepam appears to have a specific role as an adjuvant analgesic for pain due to skeletal muscle spasm associated with painful vertebral metastases.

[Mydeton: a centrally acting muscle relaxant drug from Gedeon Richter LTD]

Since its introduction in 1959 tolperisone hydrochloride (Mydeton) is still one of the leading products of Gedeon Richter Ltd. It has been successfully applied for treating different painful muscle spasms. The compound is successfully marketed also by several foreign, mostly Japanese, pharmaceutical companies, as a central muscle relaxant agent. The present summary overviews the pharmacology of tolperisone, with special emphasize on its still partly understood way of action. Data from the scientific literature as well as our own experimental results strongly support the hypothesis that inhibition of voltage gated sodium channels is a major component of the mechanism of action of tolperisone. The paper also summarizes the clinical results with tolperisone and the perspectives of the therapeutic use of centrally acting muscle relaxants.

The 5-HT(1A) receptor agonist F 13640 attenuates mechanical allodynia in a rat model of trigeminal neuropathic pain

The effects of acute intraperitoneal injections of the 5-HT(1A) receptor agonists F 13640 [(3-chloro-4-fluoro-phenyl)-[4-fluoro-4-[[(5-methyl-pyridin-2-ylmethyl)-amino]-methyl]piperidin-1-yl]-methadone] and F 13714 [3-chloro-4-fluorophenyl-(4-fluoro-4-[[(5-methyl-6-methylamino-pyridin-2-ylmethyl)-amino]-methyl]-piperidin-1-yl-methanone] were studied in comparison with those of baclofen and morphine on responsiveness to von Frey hair stimulation after chronic constriction injury to the rat's infraorbital nerve (IoN-CCI). Following IoN-CCI, an ipsilateral hyperresponsiveness developed that remained stable in control rats throughout the period of drug testing. F 13640, F 13714, baclofen and morphine dose-dependently decreased the hyperresponsiveness; normalization of the response occurred at doses 0.63, 0.04, 5 and 10 mg/kg, respectively. Confirming earlier data, baclofen's effects further validate IoN-CCI as a model of trigeminal neuralgia. The effects of F 13640 and F 13714 are initial evidence that 5-HT(1A) receptor agonists produce profound analgesia in the IoN-CCI model. The present data extend recent evidence that high-efficacy 5-HT(1A) receptor activation constitutes a new mechanism of central analgesia the spectrum of which may also encompass trigeminal neuropathic pain.

Effects of treatment with oxytocin, xylazine butorphanol, guaifenesin, acepromazine, and detomidine on esophageal manometric pressure in conscious horses

OBJECTIVE

To compare effects of oxytocin, acepromazine maleate, xylazine hydrochloride-butorphanol tartrate, guaifenesin, and detomidine hydrochloride on esophageal manometric pressure in horses.

ANIMALS

8 healthy adult horses.

PROCEDURE

A nasogastric tube, modified with 3 polyethylene tubes that exited at the postpharyngeal area, thoracic inlet, and distal portion of the esophagus, was fitted for each horse. Amplitude, duration, and rate of propagation of pressure waveforms induced by swallows were measured at 5, 10, 20, 30, and 40 minutes after administration of oxytocin, detomidine, acepromazine, xylazine-butorphanol, guaifenesin, or saline (0.9% NaCI) solution. Number of spontaneous swallows, spontaneous events (contractions that occurred in the absence of a swallow stimulus), and high-pressure events (sustained increases in baseline pressure of > 10 mm Hg) were compared before and after drug adminision.

RESULTS

At 5 minutes after administration, detomidine increased waveform amplitude and decreased waveform duration at the thoracic inlet. At 10 minutes after administration, detomidine increased waveform duration at the thoracic inlet. Acepromazine administration increased the number of spontaneous events at the thoracic inlet and distal portion of the esophagus. Acepromazine and detomidine administration increased the number of high-pressure events at the thoracic inlet. Guaifenesin administration increased the number of spontaneous events at the thoracic inlet. Xylazine-butorphanol, detomidine, acepromazine, and guaifenesin administration decreased the number of spontaneous swallows.

CONCLUSIONS AND CLINICAL RELEVANCE

Detomidine, acepromazine, and a combination of xylazine butorphanol had the greatest effect on esophageal motility when evaluated manometrically. Reduction in spontaneous swallowing and changes in normal, coordinated peristaltic activity are the most clinically relevant effects.

RhoA kinase and protein kinase C participate in regulation of rabbit stomach fundus smooth muscle contraction

1. The degree to which the RhoA kinase (ROK) blockers, Y-27632 (1 micro M) and HA-1077 (10 micro M), and the PKC blocker, GF-109203X (1 micro M), reduced force produced by carbachol, a muscarinic receptor agonist, and phenylephrine, an alpha-adrenoceptor agonist, was examined in rabbit stomach fundus smooth muscle. 2. When examining the effect on cumulative carbachol concentration-response curves (CRCs), ROK and PKC blockers shifted the potency EC50 to the right but did not reduce the maximum response. 3. In a single-dose carbachol protocol using moderate ( approximately EC50 and maximum carbachol concentrations, Y-27632 and HA-1077 reduced peak force, but GF-109203X had no effect. By contrast, all three agents inhibited the carbachol contractions of rabbit bladder (detrusor) smooth muscle. 4. Compared to carbachol, phenylephrine produced a weaker maximum response that was not inhibited by phentolamine, atropine nor capsaicin but was inhibited by Y-27632, HA-1077 and GF-109203X. 5. In detrusor, classical down-regulation occurred, but in fundus, up-regulation of responsiveness occurred. This up-regulation in fundus may have been a post-receptor event, because a KCl-induced contraction produced after a carbachol CRC was stronger than one produced before the carbachol stimulus. 6. In conclusion, these data suggest that ROK plays a critical role in the regulation of rabbit fundus smooth muscle contraction, which is distinct from chicken gizzard smooth muscle, where ROK is reported to exist but to not play a role in muscarinic receptor-induced contraction. Additional unique findings are that PKC participates in phenylephrine- but not carbachol-induced contraction in fundus, that carbachol does not activate identical subcellular signalling systems in fundus and detrusor, and that fundus, unlike detrusor, responds to carbachol stimulation with post-receptor up-regulation of contraction.

Pharmacological activity of hyperforin acetate in rats

Hyperforin, the main antidepressant component of Hypericum extract, is not stable with regard to heat and light. Therefore, we investigated a newly synthetized derivative, hyperforin acetate. Herein we demonstrate its efficacy in animal models sensitive to antidepressant and anxiolytic drugs. In the forced swimming test, triple administration of hyperforin (5-20 mg/kg) significantly reduced the immobility time of rats, while in the learned helplessness test a daily treatment of 10 mg/kg for seven consecutive days was necessary to elicit an antidepressant effect. In the elevated plus-maze and in the light-dark test, the acute administration of hyperforin acetate (3-5 mg/kg) exerted an anxiolytic activity, which, however, was smaller than that of diazepam. The effect was inhibited by the pretreatment of rats with metergoline, a serotoninergic antagonist, but not with CGS-8216, a benzodiazepine receptor antagonist. Hyperforin acetate (3-10 mg/kg) was also able to reduce locomotion in rats without eliciting myorelaxant activity. As Hypericum extract was claimed to exert a potential influence on the liver drug metabolizing system, we showed that neither acute nor repeated oral doses of hyperforin acetate altered pentobarbital sleeping time in rats. Taken together, the present results show that hyperforin acetate is a pharmacologically active derivative of hyperforin and may be a starting point from which to develop new compounds for therapeutic purposes.