Phosphodiesterase-III-inhibition with amrinone leads to contracture development in skeletal muscle preparations of malignant hyperthermia susceptible swine.

BACKGROUND AND OBJECTIVE: The phosphodiesterase-III (PDE-III) inhibitor enoximone-induced marked contractures in skeletal muscle specimens of malignant hyperthermia (MH) susceptible (MHS) human beings and swine. Whether this is a substance specific effect of enoximone or caused by inhibition of PDE-III remained unclear. Therefore, the effects of the PDE-III inhibitor amrinone in porcine MH normal (MHN) and MHS skeletal muscles were investigated. METHODS: MH-trigger-free general anaesthesia was performed in eight MHS and eight MHN swine. The MH status of the swine was determined by detection of the Arg615-Cys point mutation on chromosome 6 indicating MH susceptibility. Skeletal muscle specimens were excised for the in vitro contracture tests with amrinone. Amrinone was added cumulatively every 5 min to muscle specimens in order to obtain organ bath concentrations between 20 and 400 micromol L(-1). The in vitro effects of amrinone on muscle contractures and twitches were measured. RESULTS: Amrinone-induced contractures in all skeletal muscle preparations. MHS muscles developed contractures at significantly lower bath concentrations of amrinone than MHN muscles. Contractures of MHS compared to MHN muscles were significantly larger at bath concentrations of 80, 100, 150, 200 and 400 micromol L(-1) amrinone. Muscle twitches remained unchanged up to and including 200 micromol L(-1) amrinone. CONCLUSIONS: Inhibition of PDE-III in general elicited higher contractures in MHS than in MHN muscles. Therefore, a contribution of PDE-III and the cyclic adenosine monophosphate (cAMP) system in the pathophysiology of MH must be suspected.

[Theophylline induces contractures in porcine skeletal muscle preparations with the disposition to malignant hyperthermia]. / Theophyllin induziert Kontrakturen an Skelettmuskelpräparaten des Schweines mit Disposition zu Maligner Hyperthermie.

OBJECTIVE: Theophylline, a methylxanthine, leads to an increase of the cytoplasmic Ca(2+)-concentration in the muscle cell. Since the in-vitro contracture test (IVCT) with halothane and caffeine does not distinguish a 100% between malignant hyperthermia susceptible (MHS) and non-susceptible (MHN), we examined the in-vitro effects of theophylline in porcine skeletal muscle preparations. METHODS: After approval by the local animal care committee ten MHS- and nine MHN-swine were anaesthetized and muscle biopsies taken. For IVCT, muscle specimens were exposed to bolus administrations of theophylline in concentrations of 3.0 respectively 5.0 mmol/l. Muscle contracture development and twitch amplitudes were recorded over a period of 30 minutes. Data are expressed as medians and ranges. RESULTS: After both theophylline bolus administrations MHS-muscles developed significantly higher contractures compared to the MHN-specimens. The MHS-muscles reached a maximum contracture of 17.0 mN (7.2-59.6 mN) after administration of 3.0 mmol/l theophylline. In comparison, two MHN-specimens showed weak contractures with a maximum of 1.4 mN. The 5.0 mmol/l theophylline IVCT resulted in maximum contractures of 19.1 mN (2.1-39.2 mN) for the MHS-preparations. Just in three MHN-muscles weak contractures of 0.0 mN (0.0-0.8 mN) were recorded. Thus, a significant difference without overlap was revealed for the maximum contracture. CONCLUSION: Theophylline in concentrations of 3.0 and 5.0 mmol/l revealed a clear difference between MHS- and MHN-porcine muscle preparations. Further examinations on human skeletal muscles are needed to demonstrate the value of theophylline in the IVCT MH-diagnosis.

Dantrolene--a review of its pharmacology, therapeutic use and new developments.

Human malignant hyperthermia is a life-threatening genetic sensitivity of skeletal muscles to volatile anaesthetics and depolarizing neuromuscular blocking drugs occurring during or after anaesthesia. The skeletal muscle relaxant dantrolene is the only currently available drug for specific and effective therapy of this syndrome in man. After its introduction, the mortality of malignant hyperthermia decreased from 80% in the 1960s to < 10% today. It was soon discovered that dantrolene depresses the intrinsic mechanisms of excitation-contraction coupling in skeletal muscle. However, its precise mechanism of action and its molecular targets are still incompletely known. Recent studies have identified the ryanodine receptor as a dantrolene-binding site. A direct or indirect inhibition of the ryanodine receptor, the major calcium release channel of the skeletal muscle sarcoplasmic reticulum, is thought to be fundamental in the molecular action of dantrolene in decreasing intracellular calcium concentration. Dantrolene is not only used for the treatment of malignant hyperthermia, but also in the management of neuroleptic malignant syndrome, spasticity and Ecstasy intoxication. The main disadvantage of dantrolene is its poor water solubility, and hence difficulties are experienced in rapidly preparing intravenous solutions in emergency situations. Due to economic considerations, no other similar drugs have been introduced into routine clinical practice.

[Is a presymptomatic malignant hyperthermia in-vitro diagnosis with 4-chloro-3-ethyl phenol possible? A study using porcine skeletal preparations]. / Ist eine präsymptomatische Maligne Hyperthermie in-vitro Diagnostik mit 4-Chlor-3-Ethylphenol möglich? Eine Studie an Skelettmuskelpräparaten des Schweins.

OBJECTIVE: The diagnosis of malignant hyperthermia is currently performed with the in-vitro contracture test (IVCT) with halothane and caffeine. This test has a sensitivity of 99.0 % but only a specificity of 93.6 %. A cumulative IVCT with 4-chloro-3-ethyl-phenole (CEP) has recently been shown to differentiate between MH susceptible (MHS) and MH normal (MHN) swine. The pur-pose of this study was to investigate the ability of bolus CEP-applications to distinguish between porcine MHS- and MHN-muscle specimens using the IVCT. METHODS: After approval by the local animal care committee 8 MHS- and 8 MHN-swine were anaesthetized and muscle biopsies taken. For IVCT, muscle specimens were exposed to bolus administration of CEP in concentrations of 75 resp. 100 micro mol l (-1). Predefined parameters were: (1) onset time of the contracture development, (2) time to the achievement of the 2, 5 and 10 mN contracture level and (3) maximum contracture level. Data are expressed as medians and ranges. RESULTS: After 75 micro mol l (-1) CEP administration all MHS-muscles showed contractures after 0.5 min (0.2 min/0.9 min). The 2 mN contracture level was reached by all MHS-, the 5 mN level by four MHS- and the 10 mN level by one MHS-specimen. The maximum contracture was 5.3 mN (2.4 mN/12.9 mN). The onset time after 100 micro mol l (-1) CEP was registered as 0.3 min (0.1 min/0.7 min) in the MHS-preparations. Again, the 2 mN level was achieved by all MHS-specimens, the 5 mN level by 5 and the 10 mN level by one MHS-bundle. The maximum contracture was measured as 5.9 mN (2.8 mN/13.9 mN). In 7 MHN-specimens no contracture development was measured. After 75 micro mol l (-1) CEP one MHN-muscle showed a maximum contracture of 1.0 mN, after 100 micro mol l (-1) CEP one MHN-bundle demonstrated a maximum contracture of 1.1 mN. Hence, a significant difference between MHS and MHN without overlap was revealed with both CEP-concentrations in the onset time of contracture, in the 2 mN contracture level and the maximum contracture. CONCLUSION: Since a clear differentiation between MHS and MHN porcine specimens was achieved after bolus application of 75 and 100 micro mol l (-1) CEP, MH-diagnosis might be possible with a CEP-IVCT. It seems worthwhile to examine this hypothesis in men.

Effects of a 5HT(2) receptor agonist on anaesthetized pigs susceptible to malignant hyperthermia.

BACKGROUND: The pathophysiology of the serotoninergic system in malignant hyperthermia (MH) is not completely understood. The serotonin-2 (5HT(2A)) receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI) induces typical MH symptoms, including skeletal muscle rigidity, an increase in body temperature, hyperventilation and acidosis in conscious MH-susceptible (MHS) pigs. Whether these symptoms are directly generated in skeletal muscle, result from central serotonergic overstimulation or from a porcine stress syndrome remains unresolved. In this study the in vivo effects of DOI on anaesthetized (and thus stress-protected) MHS and MH-normal (MHN) pigs were investigated. METHODS: and results. DOI 1 mg kg(-1) was administered three times at 40-min intervals to five MHS and five MHN anaesthetized pigs. Body temperature, heart rate, muscle tone, arterial carbon dioxide pressure (Pa(CO(2))), pH and creatine kinase concentrations were measured. The clinical occurrence of MH was defined by Pa(CO(2)) above 70 mm Hg and an increase in body temperature of more than 2 degrees C. Intragroup differences were analysed with the Friedman test as an overall non-parametric ANOVA and, in case of significance, with the Wilcoxon test. Intergroup comparisons were performed with the Mann-Whitney U-test (statistical significance P<0.05). MHS and MHN pigs developed muscle fasciculations, significant increases in body temperature and Pa(CO(2)) and a significant decrease in pH after the administration of DOI. These changes were comparable in both groups until the third dose of DOI, when in MHS pigs heart rate and Pa(CO(2)) rose significantly and pH fell significantly compared with MHN pigs. All MHS pigs fulfilled the MH criteria. Body temperature increased by more than 2 degrees C in all MHN pigs and Pa(CO(2)) exceeded 70 mm Hg in two. Thus, two MHN pigs fulfilled the criteria of MH. CONCLUSIONS: The comparability of the clinical presentation following DOI administration in MHS and MHN animals and the order of the development of MH-like symptoms favour the hypothesis of a central serotonergic overstimulation, leading to a serotonin syndrome.

Multicentre evaluation of in vitro contracture testing with bolus administration of 4-chloro-m-cresol for diagnosis of malignant hyperthermia susceptibility.

BACKGROUND AND OBJECTIVE: The in vitro contracture test with halothane and caffeine is the gold standard for the diagnosis of susceptibility to malignant hyperthermia (MH). However, the sensitivity of the in vitro contracture test is between 97 and 99% and its specificity is 78-94% with the consequence that false-negative as well as false-positive test results are possible. 4-Chloro-m-cresol is potentially a more specific test drug for the in vitro contracture test than halothane or caffeine. This multicentre study was designed to investigate whether an in vitro contracture test with bolus administration of 4-chloro-m-cresol can improve the accuracy of the diagnosis of susceptibility to MH. METHODS: Three hundred and fifty-two patients from 11 European MH laboratories participated in the study. The patients were first classified as MH susceptible, MH normal or MH equivocal by the in vitro contracture test according to the European MH protocol. Muscle specimens surplus to diagnostic requirements were used in this study (MH susceptible = 103 viable samples; MH equivocal = 51; MH normal = 204). 4-Chloro-m-cresol was added to achieve a concentration of 75 micromol L(-1) in the tissue bath. The in vitro effects on contracture development and muscle twitch were observed for 60 min. RESULTS: After bolus administration of 4-chloro-m-cresol, 75 micromol L(-1), 99 of 103 MH-susceptible specimens developed marked muscle contractures. In contrast, only two of 204 MH-normal specimens showed an insignificant contracture development following 4-chloro-m-cresol. From these results, a sensitivity rate of 96.1% and a specificity rate of 99.0% can be calculated for the in vitro contracture test with bolus administration of 4-chloro-m-cresol 75 micromol L(-1). Forty-three patients were diagnosed as MH equivocal, but only specimens from 16 patients developed contractures in response to 4-chloro-m-cresol, indicating susceptibility to MH. CONCLUSIONS: The in vitro contracture test with halothane and caffeine is well standardized in the European and North American test protocols. However, this conventional test method is associated with the risk of false test results. Therefore, an improvement in the diagnosis of MH is needed. Regarding the results from this multicentre study, the use of 4-chloro-m-cresol could increase the reliability of in vitro contracture testing.

[In-vitro-effects of cocaine in skeletal muscle specimens of patients susceptible to malignant hyperthermia]. / In-vitro-Effekte von Kokain an Skelettmuskelpräparaten von Patienten mit Veranlagung zuMaligner Hyperthermie.

OBJECTIVE: The abuse of cocaine can cause serious medical complications like tachycardia, rhabdomyolysis, and hyperthermia. Because of the clinical similarities, it has been suggested that cocaine might be a trigger of malignant hyperthermia (MH). Therefore, aim of this study was to investigate the in-vitro effects of cocaine in skeletal muscle specimens of MH susceptible (MHS) and normal (MHN) patients. METHODS: 62 patients undergoing the in-vitro contracture test (IVCT) according to the protocol of the European MH Group (EMHG) for diagnosis of MH susceptibility were included in this study. In muscle specimens surplus to diagnostic requirements cocaine was added in order to achieve tissue bath concentrations of 0.01, 0.1 and 1.0 mM. The contracture development and twitch response have been registered. RESULTS: 21 patients were diagnosed as MHS and 36 patients as MHN. 5 patients tested as MH-equivocal (MHE) were excluded from the study. Following bolus administration of cocaine, no contracture development was observed in MHS, as well as MHN specimens. The muscle twitch decreased after cocaine administration significantly in both diagnostic groups. CONCLUSION: In contrast to the established MH trigger substances like volatile anaesthetics, cocaine produced no contracture development in MHS muscle specimens. Furthermore, cocaine produced a negative inotropic effect in all skeletal muscle preparations, which might be explained by local anaesthetic effects. Regarding these results, cocaine seems not to be a MH trigger agent.

Effects of the phosphodiesterase-III inhibitor enoximone on skeletal muscle specimens from malignant hyperthermia susceptible patients.

STUDY OBJECTIVES: To study the in vitro effects of the phosphodiesterase-III inhibitor enoximone on skeletal muscle specimens from malignant hyperthermia susceptible (MHS) and normal (MHN) patients. DESIGN: Prospective study. SETTING: Malignant hyperthermia (MH) laboratory at a university hospital. PATIENTS: 47 patients with clinical suspicion for MH undergoing in vitro contracture test (IVCT) for diagnosis of MH susceptibility. INTERVENTIONS: Biopsies of M. quadriceps femoris were performed in adult patients with a 3-in-1 nerve block and in children with trigger-free general anesthesia. MEASUREMENTS AND MAIN RESULT: Patients were first classified as MHS or MHN by the IVCT according to the protocol of the European MH Group (EMHG). Patients with equivocal results (MHE) or with neuromuscular diseases were excluded from the study. Enoximone was added to the organ bath to surplus vital muscle specimens in single bolus concentrations of 0.4, 0.6, 0. 8, or 1.6 mmol/L. The in vitro effects of enoximone on muscle contractures and twitch were measured. Seventeen patients were classified as MHS and 30 as MHN by the EMHG criteria. Enoximone induced contractures in skeletal muscles in a dose-dependent manner. Contractures of MHS compared to MHN muscle specimens were significantly larger at all concentrations used in this study. No overlap in maximum contractures was seen between MHS and MHN muscles at a bath concentration of 0.6 mmol/L enoximone only. CONCLUSIONS: Diagnosis of MH by an IVCT test with a single bolus administration of enoximone seems to be possible using a concentration of 0.6 mmol/L. The findings of this study may indicate an involvement of the phosphodiesterase-III and cAMP system in pathogenesis of MH. Further in vivo investigation should determine the trigger potency of enoximone in MH susceptible individuals.

5-HT2 receptor antagonist-mediated inhibition of halothane-induced contractures in skeletal muscle specimens from malignant hyperthermia susceptible patients.

Administration of 5-HT2 receptor agonists induced malignant hyperthermia (MH) in susceptible pigs. Furthermore, the 5-HT2 receptor antagonist ritanserin prevented 5-HT-induced porcine MH. It has been shown that 5-HT2 receptor agonists induce marked contractures in skeletal muscle specimens from MH susceptible (MHS) but not in specimens from normal patients. The purpose of this study was to investigate the effects of ritanserin on halothane-induced contractures in muscle specimens from MHS patients. Twenty-five patients aged 8-56 years (29.5+/-13.6) classified as MHS by the in vitro contracture test (IVCT) with halothane and caffeine according to the protocol of the European MH Group participated in this study. Muscle specimens were pretreated with ritanserin 10 micromol/l (n= 14), 20 micromol/l (n=14) and 100 micromol/l (n=12) for 10 min and subsequently halothane was added incrementally (0.11-0.22-0.44 mmol/l) to the tissue bath as described in the European MH protocol. The results of the halothane contracture test were used as control. Following administration of halothane, muscle contractures reached a maximum of 16.9+/-4.2 mN. Ritanserin led to a significant inhibition of halothane-induced contractures in MHS muscles. Following pretreatment with ritanserin, halothane-induced contracture maximum was significantly smaller with 7.5+/-3.1 mN after 10 micromol/l ritanserin, 4.9+/-1.5 mN after 20 micromol/l ritanserin and 0.5+/- 0.2 mN after 100 micromol/l ritanserin than without pretreatment. Administration of ritanserin induced at all concentrations a decrease in muscle twitch height. Increase in muscle twitch following halothane was reduced in a concentration-dependent manner by ritanserin. The presented findings indicate that 5-HT might be involved in the mechanisms of halothane-induced MH in humans. Further studies have to determine the pathophysiological role of the 5-HT system in MH, and whether ritanserin could be an alternative for treatment or prevention of halothane-induced MH.

4-chloro-m-cresol is a trigger of malignant hyperthermia in susceptible swine.

BACKGROUND: 4-Chloro-m-cresol (4-CmC) induces marked contractures in skeletal muscle specimens from individuals susceptible to malignant hyperthermia (MHS). In contrast, 4-CmC induces only small contractures in specimens from normal (MHN) patients. 4-CmC is a preservative within a large number of commercially available drug-preparations (e.g., insulin, heparin, succinylcholine), and it has been suggested that 4-CmC might trigger malignant hyperthermia. This study was designed to investigate the effects of 4-CmC in vivo and in vitro in the same animals. METHODS: After approval of the animal care committee, six Pietrain MHS and six control (MHN) swine were anesthetized with azaperone 4 mg/kg intramuscularly and metomidate 10 mg/kg intraperitoneally. After endotracheal intubation, lungs were mechanically ventilated (inspired oxygen fraction 0.3) and anesthesia was maintained with etomidate 2.5 mg x kg(-1) x h(-1) and fentanyl 50 microg x kg(-1) x h(-1). Animals were surgically prepared with arterial and central venous catheters for measurement of hemodynamic parameters and to obtain blood samples. Before exposure to 4-CmC in vivo, muscle specimens were excised for in vitro contracture tests with 4-CmC in concentrations of 75 and 200 microM. Subsequently, pigs were exposed to cumulative administration of 3, 6, 12, 24, and 48 mg/kg 4-CmC intravenously. If an unequivocal episode of malignant hyperthermia occurred, as indicated by venous carbon dioxide concentration > or = 70 mmHg, pH < or = 7.25, and an increase of temperature > or = 2 degrees C, the animals were treated with dantrolene, 3.5 mg/kg. RESULTS: All MHS swine developed malignant hyperthermia after administration of 4-CmC in doses of 12 or 24 mg/kg. Venous carbon dioxide concentration significantly increased and pH significantly decreased. Temperature increased in all MHS animals more than 2 degrees C. Blood lactate concentrations and creatine kinase levels were significantly elevated. All MHS swine were treated successfully with dantrolene. In contrast, no MHN swine developed signs of malignant hyperthermia. After receiving 4-CmC in a concentration of 48 mg/kg, however, all MHN animals died by ventricular fibrillation. The in vitro experiments showed that both concentrations of 4-CmC produced significantly greater contractures in MHS than in MHN specimens. CONCLUSIONS: 4-CmC is in vivo a trigger of malignant hyperthermia in swine. However, the 4-CmC doses required for induction of malignant hyperthermia were between 12 and 24 mg/kg, which is about 150-fold higher than the 4-CmC concentrations within clinically used preparations.