Studies on the mechanism of action of dantrolene sodium

Summary In rat diaphragm-phrenic nerve preparations, dantrolene sodium has been shown to have no effect on neuromuscular transmission. KCl and acetylcholine contractures in the frog rectus muscle are depressed in the presence of dantrolene sodium. The threshold for caffeine contractures in the frog sartorius and rectus muscles is raised from 2.0 to 4.0 mM. In isolated frog sartorius muscles, the tetanic fusion frequency is increased by 29%, and the twitch response is depressed more than the tetanic.According to these observations it is proposed that the muscle relaxant properties of dantrolene sodium are dependent on its direct inhibitory action on skeletal muscle. It is further hypothesized that this direct action results from an antagonism of calcium release within the muscle.     

Effect of dantrolene sodium upon the activity of the hind leg muscle of the cat with local tetanus

Summary Cats with local tetanus were i.v. injected with dantrolene sodium. There is no effect of dantrolene sodium on the electromyogram in response to indirect stimulation of the non-poisoned muscle nor on the increased spontaneous activity of the poisoned muscle. The tension of the muscle, however, was strongly reduced.     

The effect of dantrolene sodium on rat skeletal muscle in relation to the plasma concentration.

Dantrolene sodium is a muscle relaxant used in the treatment of spasticity. It has been shown to interfere with calcium release from the sarcoplasmic reticulum and thus to inhibit excitation--contraction coupling. The effect of dantrolene sodium on the twitch tension of the tibialis anterior muscle of the rat was measured after 2 mg/kg i.v. or 25 mg/kg orally. Plasma concentrations were estimated at maximum twitch depression and during recovery from the block. In a separate series of experiments the half-life of labelled dantrolene sodium was measured in blood plasma, skeletal muscle and heart muscle of rats. Dantrolene sodium 2 mg/kg i.v. gave a maximal block of approximately 47%, the mean dantrolene sodium concentration was then 5.8 microgram/ml. A half-life for distribution of 1.1 min and an elimination half-life of 31 min after intravenous administration were observed, elimination rate constants in skeletal and heart muscle were comparable. Recovery from the block went much slower, the half-time of the process being approximately 80 min. Dantrolene sodium 25 mg/kg orally gave a maximal block of approximately 38% at a mean plasma concentration of 3.6 microgram/ml after 14 min. The recovery was again very slow. These experiments demonstrated that dantrolene sodium acts according to a two-compartment pharmacokinetic model. There was a discrepancy between duration of effect and plasma concentration of dantrolene sodium in the rat. This suggests that the receptor for dantrolene sodium is not located in the central compartment.     

Inter-relationships between the absorptions of hydrocortisone,sodium, water and actively transported organic solutes in the human jejunum

Summary The effect of intraluminal hydrocortisone (100 mg/l) on sodium and water transport in the small intestine was investigated by jejunal perfusion (flow rate 15 ml/min) of healthy subjects with normal saline and saline containing 56 mmol/l galactose or alanine. Minimal absorption of sodium and water occurred with normal saline and did not change significantly in the presence of hydrocortisone. Galactose and alanine enhanced sodium and water absorption and further significant increases occurred in the presence of hydrocortisone. Glucocorticoidinduced increases in absorption were detected within 20–30 min, while plasma cortisol concentrations were in the normal range. 43% of the perfused dose of hydrocortisone was absorbed with normal saline (p<0.01). There was a significant positive correlation (p<0.0025) between hydrocortisone and water absorption. Thus, in the presence of actively absorbed organic solutes, hydrocortisone rapidly increased sodium absorption and the concurrent increase in water absorption appears to have facilitated passive absorption of hydrocortisone.     

Excitation-contraction uncoupling in skeletal muscle by dantrolene sodium

Summary Dantrolene sodium, a skeletal muscle relaxant, inhibits the twitch response by direct action on the muscle. The action potentials from dantrolene sodium depressed muscles have been examined by taking their first derivative, and membrane capacitance has been measured with cable analysis techniques. It is concluded that dantrolene sodium has no effect on the electrical excitability of the muscle and uncouples excitation-contraction mechanisms.     

HPLC-DAD法测定家兔关节液中头孢唑林钠的含量

本实验建立了一种灵敏且专属的HPLC-DAD测定家兔关节液中头孢唑林钠的方法。用乙腈沉淀关节液中的蛋白质,安替比林作为内标。样品在戴安U3000高效液相色谱仪上操作,并用菲罗门Luna C18（150 mm×4.60 mm,5μm,100 A）柱分离,流动相为0.1%甲酸水和乙腈,流速为1 mL/min,检测波长为272 nm,柱温为25 oC。在1.0–100.0μg/mL范围内,头孢唑林钠和内标安替比林的峰面积比值与浓度线性关系良好（r 2=0.9999）,最低检测限为（LOD,S/N=3）为0.07μg/mL,最低定量限（LOD,S/N=10）为0.22μg/mL。头孢唑林钠回收率（低、中、高浓度）分别为124.6%、117.8%、100.6%（RSD%=1.9%,4.0%,1.1%,n=5）。日内和日间精密度在0.5%–2.7%。本实验建立的家兔关节液中头孢唑林钠HPLC-DAD分析方法简便、灵敏且可靠。此方法可以应用于家兔关节液中头孢唑林钠的测定。     

Effects of dantrolene sodium on respiratory and other muscles and on respiratory parameters in the anaesthetised cat.

The effects of intravenous dantrolene sodium on contractions of the tibialis anterior, the flexor digitorum longus, the soleus and the diaphragm muscles, and on respiratory parameters, blood pressure and heart rate were recorded in cats under chloralose anaesthesia. Dantrolene maximally depressed twitches of the tibialis anterior and flexor digitorum loncles to a significantly greater extent (ca. 90%) than it depressed those of the soleus and diaphragm muscles (ca. 72%). When the muscles were indirectly stimulated at frequencies high enough to produce complete fusion of responses, the depressant action of dantrolene was largely masked. The onset of this “break through” effect was evident with paired stimuli, and was maximal with trains of about 6 stimuli. Dantrolene was without effect on blood pressure and heart rate in all experiments; the slight effects that accompanied each injection were entirely attributable to the solvent (propylene glycol). In 8 out of 12 experiments, dantrolene was without any detectable effect on breathing. In one cat, however, which happened to be unusually deeply anaesthetised, dantrolene produced a decrease in the frequency of breathing and the animal tended to hold each breath for longer than usual. In 3 out of the 12 cats, dantrolene produced a slight increase in transpulmonary pressure, a slight reduction in tidal volume and a slight shortening of the duration of each respiratory cycle with no alteration in the frequency of breathing. It is proposed that the lack of effect of dantrolene on the respiratory parameters in most experiments was the result of a reflex increase in the frequency of discharge from the respiratory centre to the extent that resistant tetanic contractions of the respiratory muscles were evoked.     

CP-96,345, a non-peptide antagonist of substance P: I. Effects on the actions mediated by substance P and related tachykinins on the guinea-pig ileum and rabbit jejunum

Summary The effects of a non-peptide antagonist of substance P, CP 96,345, were investigated, in vitro, on the guinea-pig ileum and the rabbit jejunum.Contractions of the guinea-pig ileum, induced by substance P and neurokinin A, were specifically inhibited by the racemate (±)CP-96,345 (pIC₅₀ 7.8 and 7.3, respectively). The inhibition by (±)CP-96,345 of contractions evoked by neurokinin B and by bradykinin (pIC₅₀ 6.1 and 4.9, respectively) was attributed to unspecific effects of the antagonist. The inhibition of substance P-induced contractions of the rabbit jejunum required a 10 times higher concentration of (±)CP-96,345 (pIC₅₀ = 6.8) than was required with the guinea-pig ileum. The plateau phase of contraction of the guinea-pig ileum induced by high concentrations of substance P, neurokinin A or neurokinin B, which is known to be mediated through tachykinin receptors on intrinsic cholinergic neurones, was inhibited by 200 nM (±)CP-96,345 but not by the inactive enantiomer, CP-96,344. This indicates a specific inhibition of these neuronal tachykinin receptors by (±)CP-96,345 Contractions known to be mediated by the release of substance P, such as those evoked by capsaicin and by mesenteric nerve or field stimulation, were partially inhibited by (±)CP-96,345 at concentrations of 200 to 600 nM. Unspecific inhibitory effects of CP-96,345, in concentrations of 1 µM or higher, were observed on histamine-induced contractions, and on the cholinergic twitch response to electrical stimulation, of the guinea-pig ileum. Therefore, an inhibition by CP-96,345 of substance P-related effects can only be regarded as specific if the concentration of the antagonist is below 1 µM. No effect of CP-96,345 (1 µM) was seen on peristalsis in vitro. The peristaltic reflex, in situ, was also not affected by CP-96,345 (1.6 µmolkg^–1, i.v.).The present results demonstrate that, although inhibitory actions of CP-96,345 can be observed on certain motor responses in the guinea-pig small intestine, peristalsis, a physiologically relevant function, remains intact. Send offprint requests to F. Lembeck at the above address     

Muscle relaxant properties of the identified metabolites of dantrolene

Summary Identified metabolites of dantrolene, a skeletal muscle relaxant, were studied for inhibition of skeletal muscle contractions. Inhibition of muscle contractions were studied in vivo in the rat gastrocnemius muscle preparation, and in vitro using isolated rat diaphragm strips. Dantrolene (D) and 5-hydroxydantrolene (5-HD) inhibited muscle contraction responses in a dose dependent manner, both in vivo and in vitro. 5-HD was less potent than D.     

The effect of sodium deoxycholate and other surfactants on the mucosal surface pH in proximal jejunum or rat

Summary The mucosal surface pH (acid microclimate) and nucleotide levels of rat proximal jejunum were measured in vivo under various conditions which included exposure to pharmacological agents and to surfactants. Mucosal surface pH was unaffected by sodium nitroprusside, A23187 and amiloride, as was mucosal cGMP content, although amiloride and A23187 reduced cAMP content. In contrast, surfactants elevated the pH of the mucosal surface significantly (P < 0.001): control value 6.23 ± 0.02 (n = 12); Lubrol PX 0.8% (v/v) 6.98 ± 0.02 (n = 5); sodium deoxycholate 2 mmol/l 6.67 ± 0.04 (n = 5); Triton X-100 0.5% (v/v) 7.41 ± 0.03 (n = 5). No significant changes in cGMP levels were noted after surfactant treatment, although DOC and Triton X-100 reduced cAMP levels. The ability of higher concentrations of surfactant to elevate the mucosal surface pH beyond neutrality to values similar to plasma pH contrasts with the action of Escherichia coli heat-stable (STa) enterotoxin which at high concentrations could not elevate the mucosal surface pH beyond neutrality. Consistent with the known effects on tight junction permeability, surfactants may act by allowing plasma-like subepithelial fluid to neutralise the microclimate. Send offprint requests to M. L. Lucas at the above address     

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.     

In vitroantioxidant properties of dantrolene sodium

Dantrolene sodium is a skeletal muscle relaxant, which inhibits intracellular Ca2+ release from the sarcoplasmic reticulum. The aim of this study is to examine possible in vitro antioxidant effects of dantrolene sodium. For this reason, the in vitro antioxidant effects of dantrolene sodium were studied using thiocyanate methods. Additionally, the reducing power and free radical scavenging activity were determined. Dantrolene sodium showed strong antioxidant activity in the linoleic acid emulsion system. The antioxidant activity increased with an increasing amount of dantrolene sodium (50, 100, 250 microg). The 50, 100 and 250 microg samples of dantrolene sodium showed 55%, 70% and 82% inhibition on peroxidation of linoleic acid, respectively. On the other hand, the 250 microg sample of alpha-tocopherol showed 62% inhibition of peroxidation of linoleic acid. Like antioxidant activity, the reducing power of dantrolene sodium increased in a dose-dependent manner. The reducing power of dantrolene was statistically significant vs control, but lower than butylated hydroxytoluene (BHT) and quercetin. Although dantrolene sodium had free radical scavenging activity this was not statistically significant. In contrast to dantrolene sodium, quercetin and butylated hydroxyanisole (BHA) had highly potent free radical scavenging activities and those were statistically significant. According to the these results, it may be said that antioxidant effect of dantrolene sodium is more related to its antioxidant activity in linoleic acid emulsion and reducing power, than to its free radical scavenging activity. These properties may be major reasons for the inhibition of lipid peroxidation.     

Effect of diazoxide, verapamil and compound D600 on isoproterenol and calcium-mediated dose-response relationships in isolated rabbit atrium.

The effect of diazoxide, verapamil and compound D600 on calcium and isoproterenol dose-response relationships was investigated in isolated rabbit atrial preparations. All three agents shifted calcium dose-force relationships parallel and to the right. D600 acted as a competitive antagonist of calcium, as a plot of log (x - 1) vs. -log B resulted in a straight line with a slope of approximately -1.0. Diazoxide, verapamil and D600 also antagonized isoproterenol but in a non-competitive manner. A reduction of calcium in the bathing fluid produced a qualitatively similar non-competitive antagonism of isoproterenol and markedly potentiated diazoxide antagonism of isoproterenol. We conclude that: (1) diazoxide has calcium antagonistic properties similar to the "calcium antagonists" verapamil and D600; (2) these agents act as competitive antagonists of calcium through a specific site that is beyond the beta-adrenergic receptor and in the series of events between the beta-adrenergic receptors and inotropic response in myocardial tissue.     

Role of the cholinergic system and of apamin-sensitive Ca2+-activated K+ channels on rabbit jejunum spontaneous activity and on the inhibitory effects of adrenoceptor agonists

1 One reason why rabbit jejunum is suitable for studying the mechanisms underlying the actions of the various neurotransmitters and their interactions is its spontaneous motility. The main regulator of spontaneous motility is the cholinergic system. How the cholinergic system regulates the spontaneous activity in the rabbit jejunum and how it affects the inhibitory action of α‐ and β‐adrenoceptor agonists remains unclear. 2 We studied the influence of the cholinergic system and apamin‐sensitive Ca²⁺‐activated K⁺ channels on spontaneous contractions in the rabbit jejunum and on the inhibitory effects ofα₁‐ and β‐adrenoceptor agonists. 3 In naïve tissues, atropine (ATR, 7.4 × 10^?8 m ) and tetrodotoxin (8 × 10^?8 m ) almost completely inhibited – to a similar extent – the amplitude of spontaneous activity. Despite the presence of ATR or TDX, tissue contraction gradually recovered to about 50% of the baseline amplitude within 5–10 min. When ATR or TDX, respectively, were added to the TDX‐ or ATR‐treated tissues, the recovered activity decreased weakly but significantly. After washout and a 45‐min rest the contraction amplitude returned to baseline values. A further exposure to ATR or TDX reduced the contraction to a level significantly lower than the one obtained after TDX or ATR added 5 min after ATR or TDX, respectively. In preparations prestimulated for 10 min with acetylcholine (ACh), ATR abolished the TDX‐resistant recovered spontaneous activity. 4 Adrenaline (ADR, 0.5–5 × 10^?7 m ) and phenylephrine (PHE, 1–10 × 10^?7 m ) inhibited tissue motility in naïve and in ATR‐ and in TDX‐exposed preparations. But whereas in naïve preparations the α₁‐adrenoceptor antagonists completely antagonized inhibition induced by both drugs, in ATR‐ and TDX‐exposed tissues they did so only partially for ADR. Agonist‐induced inhibition had a rapid onset but rapidly faded; pendular movements took significantly longer to recover in ATR‐ and TDX‐treated tissues than in naïve tissues. In tissues exposed for 2 min to ADR (0.5–5 × 10^?7 m ) or PHE (1–10 × 10^?7 m ), washout or addition of α₁‐adrenoceptor antagonists caused an immediate short‐lasting increase in contraction amplitude. 5 Apamin (APAM, 5 × 10^?9 m ) caused a rapid and persistent increase in the amplitude of contractions. It also blocked the inhibitory responses to ADR and PHE, and removed washout‐induced contractions. The APAM‐induced increase in the contraction amplitude correlated with the increase obtained by washing out ADR or PHE. 6 Isoprenaline (at concentrations up to 2.8 × 10^?7 m ) produced no inhibitory response in naïve tissues, but it invariably blocked (at a concentration of 0.7 × 10^?7 m ) the recovered spontaneous activity (and sometimes depressed muscletone) in tissues exposed to ATR or TDX. Neither propranolol (3.4 × 10^?7 m ) nor APAM (5 × 10^?9 m ) counteracted these inhibitory effects. 7 These results indicate that spontaneous motility in the rabbit jejunum is predominantly mediated by neuronal release of ACh and by some other unidentified neuronal activity. Released ACh inhibits myogenic activity and strongly antagonizes β‐adrenoceptor‐induced APAM‐insensitive inhibition but leaves α₁ agonist‐induced APAM‐sensitive inhibition unchanged.     

Anti-inflammatory and antinociceptive properties of dantrolene sodium in rats and mice

Our study aimed at examining the possible anti-inflammatory and antinociceptive effects of dantrolene sodium in rats and mice. The anti-inflammatory effect of dantrolene sodium (2.5, 5 and 10 mg kg (-1)) was investigated and compared with diclofenac sodium (5 mg kg (-1)) using the formalin-, histamine-, and carrageenan-induced paw oedema and cotton pellet granuloma tests. Analgesic effects of dantrolene sodium were evaluated and compared with metamizol (200 mg kg (-1)) in acetic acid-induced writhing and formalin-induced paw licking tests. It was found that dantrolene sodium significantly diminished the nociceptive response in mice, showing at the same time considerable anti-inflammatory properties in rats.     

阿仑磷酸钠和辛伐他汀对体外培养成骨细胞的影响

目的探讨辛伐他汀和阿仑磷酸钠对体外培养成骨细胞的影响。方法分离3周龄成骨细胞，体外培养时以辛伐他汀和阿仑磷酸钠刺激，观察成骨细胞碱性磷酸酶水平和成骨细胞增殖率。结果辛伐他汀、阿仑磷酸钠可以促进成骨细胞增殖，增加碱性磷酸酶的分泌，二者共同作用后作用更显著。结论辛伐他汀和阿仑磷酸钠能促进成骨细胞增殖和分泌碱性磷酸酶，可以联合作用促进骨形成。     

Use of dantrolene in experimental scorpion envenomation by Androctonus Australis Hector

 Hyperthermia and profuse perspiration are rarely absent in severe cases of scorpion envenomation. Based on these observations, the aim of this study was to determine the therapeutic effects of dantrolene, on experimental poisoning by the venom of Androctonus australis hector. Dantrolene is a directly acting muscle relaxant which lowers the body temperature in malignant hyperthermia. The results indicate that the early use of this drug raises the LD₅₀ in experimentally poisoned mice. If these results are transposable to humans, dantrolene could be a useful therapeutic adjuvant. Received: 3 November 1994/Accepted: 5 January 1995     

Effect of dantrolene sodium in isolated guinea-pig trachea

The effect of dantrolene sodium (3 microM-0.3 mM) on the spontaneous tone and responses to various contractile agonists was studied in isolated guinea-pig trachea. Dantrolene produced a concentration-related inhibition of the spontaneous tracheal tone, reaching a value of 94.8 +/- 4.8% of the relaxation induced by caffeine 10 mM. Removal of the epithelium did not affect the dantrolene-induced relaxation. Dantrolene did not alter the concentration-response curve for KCl and produced only small displacements of the concentration-response curves for CaCl2, acetylcholine and histamine, without affecting their maximal effects. Dantrolene dose relatedly inhibited the contraction induced by caffeine (1 mM) in Krebs solution containing indomethacin (2.8 microM) at 20 degrees C. The spasm induced by caffeine in Ca2(+)-free Krebs solution (20 degrees C, indomethacin 2.8 microM) was slightly depressed by dantrolene. Dantrolene did not depress the Ca2+ (1 microM)-induced contraction in skinned trachea. These results suggest that besides a possible intracellular site of action, the mechanism of the inhibitory effect of dantrolene in guinea-pig trachea may be related to interference with Ca2+ entry through pathways not susceptible to calcium channel blockers.     

Effects of pimozide on noradrenergic transmission in rabbit isolated ear arteries.

In the rabbit ear artery both dopamine and noradrenaline inhibit stimulation-induced (S-I) transmitter noradrenaline efflux. Pimozide, which is reported to be a specific dopamine receptor antagonist, was used to further study the effects of dopamine on transmitter efflux. In a concentration of 0.2 micrometer pimozide blocked the inhibition of S-I efflux produced by 0.5 micrometer dopamine but not that produced by 0.5 micrometer noradrenaline. In a concentration of 10 nM, pimozide enhances transmitter release and vasoconstrictor responses to sympathetic nerve stimulation; this may be due to blockade of feedback inhibition of transmitter release by endogenous dopamine. In a concentration of 1 micrometer, pimozide reduced transmitter release and vasoconstrictor responses to sympathetic nerve stimulation. Vasoconstrictor responses to noradrenaline and histamine are antagonized by pimozide in a noncompetitive manner.     

阿魏酸钠对家兔心室肌单相动作电位的影响

目的　探讨阿魏酸钠对心肌细胞单相动作电位的影响。方法　健康家兔 2 0只 ,随机平均分为两组 :对照组 (苄基四氢巴马汀组 )和实验组。按传统心内膜MAP记录方法经右颈外静脉插入四极接触电极导管至家兔右心室内膜记录MAP信号并同时记录Ⅱ导联心电图。对照组经耳缘静脉给予苄基四氢巴马汀 ( 5mg·kg-1) ,实验组给予阿魏酸钠( 0 6g·kg-1) ,给药前、后观察MAPA、MAPD5 0、MAPD90及ERP。结果　对照组用药前MAPA及MAPD2 0分别为( 2 7 0 1± 0 67)mV及 ( 79 0 5± 7 0 4 )ms,用药后分别为( 2 6 87± 0 73 )mV及 ( 77 5± 7 170 )mV(P >0 0 5 ) ;用药2 0 0 1 0 2 15收稿 ,2 0 0 1 0 4 13修回1 贵州省人民医院心内科 ,贵阳　 5 5 0 0 0 22 包头钢铁职工医院 ,包头　 0 14 0 0 0作者简介 :李　屏 ,女 ,36岁 ,医学硕士 ,副主任医师。Tel:0 85 1 5 934 319,E mail:lipingb @hotmail.com ;曾秋棠 ,男 ,36岁 ,医学博士 ,副教授 ,硕士生导师前MAPD5 0、MAPD90、ERP分别为 ( 97 5± 6 770 )ms、( 12 3 5± 5 80 )ms、( 111± 13 5 0 )ms,用药后分别为 ( 12 4 5± 8 96)ms、( 15 3± 7 5 3 )ms、( 14 2± 13 3 7)ms (P <0 0 1) ;实验组用药前MAPA及MAPD2 0分别为 ( 2 6 5 8±1 0 3 )mV及 ( 75± 5 77)ms,用