Salivary cortisol: a non-invasive measure of hypothalamo-pituitary-adrenocortical activity in the squirrel monkey, Saimiri sciureus

STUDY OBJECTIVES: To study the in vitro effects of the serotonin2 (5-HT2) receptor agonist 1-(2.5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) in skeletal muscle specimens from malignant hyperthermia-susceptible (MHS) and normal (MHN) patients following pretreatment with the 5-HT2 receptor antagonist ritanserin. DESIGN: Prospective study. SETTING: Malignant hyperthermia (MH) laboratory at a university hospital. PATIENTS: 41 patients undergoing in vitro contracture test for diagnosis of MH susceptibility. INTERVENTIONS: Skeletal muscle biopsies in adult patients were performed with a 3-in-1 nerve block with 40 ml prilocaine 1%. In children, general anesthesia was induced with 50 micrograms/kg alfentanil intravenously (i.v.) and 2 to 2.5 micrograms/kg propofol i.v. and maintained with a continuous infusion of propofol (< or = 150 micrograms/kg/min) and nitrous oxide (66%) in oxygen. MEASUREMENTS AND MAIN RESULTS: Patients were first classified as MHS or MHN by the in vitro contracture test according to the European MH protocol. Surplus muscle specimens of 21 MHS and 20 MHN patients were used in this study. At first, DOI was added to the organ bath at a concentration of 0.02 mM. In the second part of the study, muscle specimens were preincubated with ritanserin 0.01 mM for 10 minutes before DOI 0.02 mM was added to the bath. Muscle specimens from all patients developed contractures after administration of DOI. The onset of contractures was significantly faster in MHS muscles, and the magnitude of contracture was significantly greater than in MHN. The muscle twitch decreased significantly in both groups after DOI. After pretreatment with ritanserin, start of contracture was significantly delayed in MHS muscles. MHN muscles failed to develop contractures. The maximum level of contracture was significantly reduced in MHS. Muscle twitch decreased also in both MHS and MHN groups. CONCLUSIONS: The findings may indicate that stimulation of 5-HT2 receptors is involved in MH induction. Furthermore, 5-HT2 receptor antagonists could possibly be effective in preventing MH. Additional studies are required to determine if administration of 5-HT2 receptor antagonists could be of additional value in the treatment or prevention of anesthetic-induced MH.     

Effects of serotonin 2 receptor agonists on skeletal muscle preparations in patients with a disposition toward malignant hyperthermia

In pigs genetically susceptible to malignant hyperthermia (MH), it has been shown that serotonin (5-HT2) receptor agonists can induce MH and "psychotic" behaviour. Both can be prevented by 5-HT2 receptor antagonists. Furthermore, free levels of serotonin in plasma increased concomitantly with clinical and laboratory parameters during halothane-induced MH in pigs. In this study the in vitro-effects of the 5-HT2 receptor agonist1-(2,5-dimethoxy-4-iodophenyl)-2-amino-propane (DOI) were investigated in muscle specimens of MH-susceptible (MHS) and normal (MHN) patients. METHODS. Muscle biopsies were obtained from 37 patients aged 5-69 years (23.6 +/- 5.3 years) with clinical suspicion for MH. The patients were first classified as MHS, MHN or MHE (MH equivocal) by the in vitro contracture test (IVCT) according to the European MH protocol. After MH classification, surplus muscle specimens were subjected to the DOI study. DOI was added to the organ bath in a concentration of 0.02 mmol/l. The in vitro effects on contracture development and muscle twitch were observed for 120 min. RESULTS. Muscle specimens of all patients developed contractures after administration of DOI. However, DOI produced an earlier development of contracture in MHS (17.0 +/- 1.8 min; n = 17) than in MHN (64.7 +/- 5.9 min; n = 15) muscles. In MHS muscles, contractures were more distinct than in MHN muscles; at the end of the experiment, contractures had reached a maximum of 12.5 +/- 0.9 mN in MHS and 5.1 +/- 0.7 mN in MHN muscles. Muscle twitch following DOI administration was reduced significantly in both MHS and MHN muscles. The results of four MHE muscles were comparable with MHS. CONCLUSION. The present study supports the assumption that an altered serotonin system might be involved in the development of MH. In further studies it should investigated whether 5-HT2 receptors of skeletal muscles from MHS subjects are disordered in function or structure. 5-HT2 receptor agonists should be considered as MH-triggering agents.     

Voltage-dependent calcium release in human malignant hyperthermia muscle fibers

Malignant hyperthermia (MH) results from a defect of calcium release control in skeletal muscle that is often caused by point mutations in the ryanodine receptor gene (RYR1). In malignant hyperthermia-susceptible (MHS) muscle, calcium release responds more sensitively to drugs such as halothane and caffeine. In addition, experiments on the porcine homolog of malignant hyperthermia (mutation Arg615Cys in RYR1) indicated a higher sensitivity to membrane depolarization. Here, we investigated depolarization-dependent calcium release under voltage clamp conditions in human MHS muscle. Segments of muscle fibers dissected from biopsies of the vastus lateralis muscle of MHN (malignant hyperthermia negative) and MHS subjects were voltage-clamped in a double vaseline gap system. Free calcium was determined with the fluorescent indicator fura-2 and converted to an estimate of the rate of SR calcium release. Both MHN and MHS fibers showed an initial peak of the release rate, a subsequent decline, and rapid turn-off after repolarization. Neither the kinetics nor the voltage dependence of calcium release showed significant deviations from controls, but the average maximal peak rate of release was about threefold larger in MHS fibers.     

4-chloro-m-cresol-induced contractures of skeletal muscle specimen from patients at risk for malignant hyperthermia

PURPOSE: 4-chloro-m-cresol (4-CmC), commonly used as preservative, has been shown to induce contractures in skeletal muscle specimens from individuals susceptible to malignant hyperthermia (MH). It has been suggested that a defect of the calcium release channel of the skeletal muscle sarcoplasmic reticulum (ryanodine receptor) in MH susceptible (MHS) patients could be responsible for this phenomenon. 4-CmC was found to be a potent activator of ryanodine receptor-mediated Ca2+ release. The aim of this study was to determine the in vitro effects of 4-CmC on muscle specimens from MHS and normal (MHN) patients, and whether contracture testing with different concentrations of 4-CmC could result in a more precise discrimination between MHS and MHN. METHODS: In this prospective study muscle biopsies were obtained from 40 patients with clinical suspicion of MH. The patients were first classified by the in vitro contracture test (IVCT) according to the European MH protocol. After MH classification, surplus muscle specimens were subjected to the 4-CmC study. RESULTS: Cumulative administration of 4-CmC (25, 50, 75, 100, 150, and 200 mumol/l) produced contractures in a concentration-dependent manner. However, contractures developed significantly earlier and were greater in MHS (n = 17) than in MHN specimens (n = 23). After bolus administration of 50, 75, and 100 mumol/l 14-CmC MHS specimens developed distinct muscle contractures. In contrast, in MHN specimens only 100 mumol/l 4-CmC produced contractures. All contracture levels following bolus administration of 100 mumol/l 4-CmC were attained significantly earlier in MHS than in MHN. There was no overlapping in the range of times between both groups. CONCLUSION: In vitro contracture testing with 4-CmC seems to be a specific method to distinguish between MHS and MHN patients. However, the question whether 4-CmC is an MH-triggering agent is not completely solved. 4-CmC is a preservative within a large number of commercially available preparations (e.g. insulin, hormones, etc.). Regarding the results of contracture testing with 4-CmC it has been suggested that 4-CmC possibly represents a high-risk agent for MHS individuals. To reduce the risk of MH in susceptible patients due to administration of chlorocresols, we recommend avoiding preparations containing the preservative 4-CmC.     

Effect of chlorocresol vs caffeine on muscle contracture in malignant hyperthermia susceptible patients

The phenotype of susceptibility to malignant hyperthermia (MHS); can only be detected reliably by the in vitro caffeine-halothane contracture test (CHCT). Enhanced sensitivity of the calcium-induced calcium release mechanism is responsible for the exaggerated contracture response of skeletal muscle fibers from MHS patients to halothane and caffeine. Chlorocresol was demonstrated to be a potent activator of Ca++ release from skeletal muscle sarcoplasmic reticulum. This effect is probably mediated through action on a ryanodine sensitive Ca++ release channel known to be more sensitive in MH. We studied the effect of chlorocresol on the mechanical contracture response of skeletal muscle from patients presenting for the in vitro CHCT. Chlorocresol induces contracture response in a concentration 1/200 of that of caffeine in muscle strips from MH patients. By adding chlorocresol to the protocol of the CHCT, there is clearer discrimination between the responses of MH patients and normal subjects can be achieved.     

Chlorocresol, an additive to commercial succinylcholine, induces contracture of human malignant hyperthermia-susceptible muscles via activation of the ryanodine receptor Ca2+ channel

BACKGROUND: A defect in the ryanodine (Ry1) receptor Ca2+ channel has been implicated as one of the possible underlying causes of malignant hyperthermia (MH), a pharmacogenetic disorder characterized by sustained muscle contracture. The disease is triggered by common halogenated anesthetics and skeletal muscle relaxants, such as succinylcholine. This study tested whether the functional properties of the Ry1 receptor Ca2+ channel are affected by chlorocresol, a preservative added to a commercial preparation of succinylcholine (Midarine) and other parenteral compounds. METHODS: In vitro contracture testing was carried out on muscle biopsies from malignant hyperthermia-susceptible (MHS) and -negative (MHN) individual according to the protocol of the European MH group. Ca2+ flux studies on isolated rabbit sarcoplasmic reticulum fractions were measured spectrophotometrically by following the A710-790 of the Ca2+ indicator antipyrylazo III. RESULTS: Chlorocresol causes muscle contracture in MHS muscles at a concentration of 25-50 microM and potentiates the caffeine contracture response in human MHS muscles. Sub-threshold (20 microM) concentrations of chlorocresol increase both the Kd and the Vmax of caffeine-induced Ca2+ release from isolated rabbit terminal cisternae. CONCLUSIONS: These data suggest that, in muscle from MHS individuals, the enhanced Ca2+ released from the sarcoplasmic reticulum may not be due to the effect of succinylcholine alone but rather to the action of the preservative chlorocresol added to the drug.     

Decreased proportion of type I myofibers in skeletal muscle of dogs with chronic heart failure

BACKGROUND: Whether biochemical and histological abnormalities of skeletal muscle (SM) develop in patients with chronic heart failure (HF) remains controversial. In the present study, dogs with chronic HF were used to examine potential alterations of SM fiber type, fiber size, number of capillaries per fiber (C/F), beta-adrenergic receptor density (Bmax), and fiber ultrastructural integrity. METHODS AND RESULTS: HF was produced in 17 dogs by sequential intracoronary microembolizations. Biopsies of the lateral head of the triceps muscle were used in all studies. Type I and type II fibers were differentiated by myofibrillar ATPase (pH 9.4 or 4.2). Bmax was assessed by radioligand binding and SM ultrastructure by transmission electron microscopy. Comparisons were made with biopsies obtained from nine control dogs. The percentage of SM type I fibers was reduced in HF dogs compared with control dogs (19 +/- 2% versus 32 +/- 5%) (p < 0.001), whereas the percentage of SM type II fibers was increased (81 +/- 2% versus 68 +/- 5%) (p < 0.001). The change in fiber type composition was not associated with a preferential atrophy or hypertrophy of either fiber type. There was no difference in SM Bmax (198.9 +/- 14.3 versus 186.8 +/- 17.3 fmol/mg protein) or in C/F (5.37 +/- 0.26 versus 5.84 +/- 0.21) between HF dogs and control dogs. No ultrastructural abnormalities were present in SM fibers of HF dogs. CONCLUSIONS: In dogs with HF, there is a decrease in the relative composition of the slow-twitch type I SM fibers and an increase in fast-twitch type II fibers. The shift in fiber type composition is not associated with preferential atrophy of either fiber type or with a reduction in C/F, beta-adrenergic receptor density, or structural abnormalities of the myofibers.     

Single soleus muscle fiber function after hindlimb unweighting in adult and aged rats

This investigation compared how hindlimb unweighting (HU) affected the contractile function of single soleus muscle fibers from 12- and 30-mo-old Fischer 344 Brown Norway F1 Hybrid rats. After 1 wk of HU, functional properties of single permeabilized fibers were studied, and, subsequently, the fiber type was established by myosin heavy chain (MHC) analysis. After HU, the relative mass of soleus declined by 12 and 19% and the relative mass of the gastrocnemius declined by 15 and 13% in 12- and 30-mo-old animals, respectively. In 12-mo-old animals, the peak active force (5.0 +/- 0.2 x10(-4) vs. 3.8 +/- 0.2 x10(-4) N) and the peak specific tension (92 +/- 4 vs. 78 +/- 3 kN/m2) were significantly reduced in the MHC type I fibers by 24 and 15%, respectively. In 30-mo-old animals, the peak active force declined by 40% (4.7 +/- 0.2 x10(-4) vs. 2.8 +/- 0. 3 x10(-4) N) and the peak specific tension declined by 30% (79 +/- 5 vs. 55 +/- 4 kN/m2). The maximal unloaded shortening velocity of the MHC type I fibers increased in 12-mo-old animals (from 1.65 +/- 0.12 to 2.59 +/- 0.26 fiber lengths/s) and in 30-mo-old animals (from 0.90 +/- 0. 09 to 1.50 +/- 0.10 fiber lengths/s) after HU. Collectively, these data suggest that the effects of HU on single soleus skeletal muscle fiber function occur in both age groups; however, the single MHC type I fibers from the older animals show greater changes than do single MHC type I fibers from younger animals.     

Fiber type composition of abdominal muscles in Japanese macaques (Macaca fuscata)

The muscle fiber composition and cross-sectional area of muscle fiber types were investigated histochemically in the abdominal muscles (rectus abdominis muscle, obliquus externus abdominis muscle, obliquus internus abdominis muscle and transversus abdominis muscle) of three Japanese macaques (Macaca fuscata). Muscle fibers were classified into three fiber types (Type I, II A and II B) by myosin ATPase activity and succinate dehydrogenase activity. Each abdominal muscle in Japanese macaques contained high proportion of Type II B fibers and there were no large differences in the fiber type composition between the abdominal muscles. The range of mean fiber type percent was 26-32% Type I, 21-22% Type II A, and 46-52% Type II B fibers. Thus, based on the histochemical fiber type composition, the separate abdominal muscles appear to have a similar functional capacity. The cross-sectional area was larger for Type II than for Type I fibers, and the areas were similar in Type II A and Type II B fibers in each muscle. The rectus abdominis showed larger fibers of each type compared to the lateral abdominal muscles. The high proportion of Type II B fibers and large fiber size for Type II B fibers suggest that the abdominal muscles of Japanese macaques have properties similar to the propulsive and locomotory muscles in the limbs.     

Diagnosis of malignant hyperthermia susceptibility. 1. The significance of in vitro susceptibility tests

Molecular genetic findings indicate genetic heterogeneity in susceptibility to malignant hyperthermia (MH). At present the in vitro contracture test (IVCT) is still the most reliable diagnostic procedure for MH susceptibility. It must be performed in a standardized fashion. METHODS. We investigated 350 patients (233 children and 117 adults) using the protocol of the European MH Group for the IVCT. The test results were classified as susceptible to MH (MHS), non-susceptible to MH (MHS), non-susceptible to MH (MHN) and equivocal (MHE), with an abnormal caffeine result designated MHEc and an abnormal halothane result designated MHEh. Reasons for the IVCT were a positive family history for MH susceptibility (n = 94), a MH reaction (n = 157), creatine kinase elevation unknown aetiology (n = 53) and different neuromuscular diseases (NMD, n = 46). Physical, neurological and laboratory work-up included serum enzymes, nerve conduction studies, electromyography and muscle biopsy evaluated by different techniques. Thirty-one children and 11 adults were MHS, while 152 children and 80 adults were MHN. MHE findings were obtained in 50 children and 26 adults. While the MHS and MHN groups are diagnostically safe, the equivocal group is not, with possible false-negative or false-positive interpretation. The high number of MHE findings most probably is explained by the high proportion of patients with NMD (53% of the children, 69% of the adults). RESULTS. In a group of 18 boys with Duchenne or Becker muscular dystrophy, ranging in age from 1.5 to 24 years, the IVCT results were twice MHS, once MHE, and MHN in the remaining 15 cases. In seven other boys with Duchenne or Becker muscular dystrophy, proven by molecular techniques, there were anaesthetic complications with MH-like symptoms. After administration of trigger substances, five out of the seven suffered a cardiac arrest, two of whom died. In the surviving five boys the IVCT results were three times MHN, once MHE and once MHS. Most probably these boys suffered from effects of succinylcholine, possibly potentiated by other trigger substances. The adverse cardiac reactions are attributed to triggered rhabdomyolysis with associated hyperkalemia but not a primary hereditary disposition to MH. CONCLUSION: In patients with NMD, MHS and MHE test results do not indicate a hereditary, heterogeneous disposition to MH; the majority will be caused by a secondary induced disturbance of calcium homoeostasis in the diseased muscle cells. These results do, however, indicate the following: (1) Patients with NMD exposed to trigger substances are at higher risk than the general population for MH-like episodes, including sudden death. (2) NMD therefore should be diagnosed as early as possible and patients should not be exposed to trigger substances when alternatives are at hand. (3) Diagnostic procedures in patients having suffered an MH-like episode should include IVCT and special investigations to exclude or substantiate other NMD. The work-up may be changed if a family member is properly classified as MH susceptible. (4) In patients with known NMD there is no indication for performing IVCT, since the results may even be misleading.     

Calcium induced contracture stimulates Na,K-pump rate in isolated sheep cardiac Purkinje fibers

By keeping intracellular Na+ (aiNa) low, the Na,K-pump can prevent Ca2+ overload of cardiomyocytes. We therefore examined whether Ca2+ stimulates Na,K-pump activity in sheep cardiac Purkinje fibers. By removing Ca2+, Mg2+ and K+, the fibers depolarized and aiNa rose to 70 mM. After addition of 6 mM Mg2+ and lowering extracellular Na2+ to 29 mM, 30mM Rb+ was added, and over 10-15 min aiNa recovered to 3-7 mM. Two load-recovery cycles were conducted in 10 fibers. During one of the cycles Ca2+ (0.1-1.0 mM) was added before Rb+, causing a contracture. During recovery aiNa fell faster during Ca2+ contracture than in control cycles. Between 30 and 20 mM the rates were -10.0+/-1.6 and -5.4+/-0.6 mM/min, respectively (P<0.05). In Ca2+-exposed fibers tension fell almost parallel with aiNa. Na, K-pump reactivation caused membrane potential (Vm) to hyperpolarize transiently to -70 mV. Ca2+ did not affect membrane conductance. For a given aiNa during reactivation, Vm was more negative during Ca2+ contracture and depolarized faster (P<0.05). Intracellular pH (pHi) fell from 7.11+/-0.05 to 6.92+/-0.08 (n.s.) during control load-recovery cycles and was 6.83+/-0.14 at the end of the Ca2+ cycles. ATP content of the fibers did not change significantly through two complete load-recovery cycles, but creatine phosphate (CrP) fell by about 40%. By fitting the data to a model incorporating the Hill equation we show that during Ca2+-induced contracture maximum Na,K-pump rate (Vmax) was increased by about 40% and aiNa that causes 50% pump activation (k0.5) was lowered from 21. 2+/-1.6 to 15.5+/-1.4 mM.     

In vitro 31P-magnetic resonance spectroscopy of muscle extracts in malignant hyperthermia-susceptible patients

BACKGROUND: It was recently suggested that malignant hyperthermia-susceptible (MHS) patients could have an elevated peak of phosphodiesters in leg muscles using in vivo phosphorus magnetic resonance spectroscopy. In the current study, analysis of the phosphodiesters of muscle extracts of MHS and malignant hyperthermia-negative patients was performed using in vitro phosphorus magnetic resonance spectroscopy to chemically identify and to compare the muscle concentrations of water-soluble compounds between the two groups with respect to the muscle fiber type composition. METHODS: Perchloric acid extracts of the vastus medialis muscle of seven MHS patients and ten malignant hyperthermia-negative patients on the basis of the European malignant hyperthermia contracture test were subjected to in vitro phosphorus magnetic resonance spectroscopy carried out at 9.4 T. In addition, chemical identification of the phosphodiester region and histologic examination of the muscle specimens were performed. RESULTS: The peak in the phosphodiester region was assigned to glycerophosphorylcholine. Muscle perchloric acid extracts of MHS patients had a significantly (P < 0.05) higher glycerophosphorylcholine to the sum of phosphocreatine and inorganic phosphate (glycerophosphorylcholine/ [phosphocreatine +inorganic phosphate]) value than those of malignant hyperthermia-negative patients. Neither a difference in the fiber type composition between the two groups nor any specific myopathy were found. CONCLUSIONS: In the absence of histologic differences between muscle specimens of MHS and malignant hyperthermia-negative patients, these results could suggest that glycerophosphorylcholine could be a marker of an impairment in the phospholipid metabolism in the skeletal muscle of MHS patients.     

Structure of the latissimus dorsi muscle and respiratory function

The aim of this study was to evaluate whether respiratory function influences the structure of the latissimus dorsi muscle (LD). Twelve patients (58 +/- 10 yr) undergoing thoracotomy were studied. Lung and respiratory muscle function were evaluated before surgery. Patients showed a forced expired volume in 1 s (FEV1) of 67 +/- 16% of the reference value, an FEV1-forced vital capacity ratio of 69 +/- 9%, a maximal inspiratory pressure of 101 +/- 21% of the reference value, and a tension-time index of the diaphragm (TTdi) of 0.04 +/- 0.02. When patients were exposed to 8% CO2 breathing, TTdi increased to 0.06 +/- 0.03 (P < 0.05). The structural analysis of LD showed that 51 +/- 5% of the fibers were type I. The diameter was 56 +/- 9 microns for type I fibers and 61 +/- 9 microns for type II fibers, whereas the hypertrophy factor was 87 +/- 94 and 172 +/- 208 for type I and II fibers, respectively. Interestingly, the histogram distribution of the LD fibers was unimodal in two of the three individuals with normal lung function and bimodal (additional mode of hypertrophic fibers) in seven of the nine patients with chronic obstructive pulmonary disease. An inverse relationship was found between the %FEV1-forced vital capacity ratio and both the diameter of the fibers (type I: r = -0.773, P < 0.005; type II: r = -0.590, P < 0.05) and the hypertrophy factors (type I: r = -0.647, P < 0.05; type II: r = -0.575, P = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Phosphatidyl choline metabolism in the frog rod photoreceptor

Single fibers isolated from frog semitendinosus muscle continued to twitch for 5-8 min in calcium-free Ringer solution containing 1 mM ethylene glycol bis (beta-aminoethyl ether)-N, N'-tetraacetic acid (EGTA). Even after twitching was completely abolished, the tension of potassium contracture was not depressed, although the time course was markedly shortened. The resting potential recorded from single fibers 10 min after immersion in EGTA-Ringer solution decreased slightly. These fibers failed to generate action potential, however, in a whole sartorius muscle the self-exchangeable calcium was not significantly reduced by 1mM EGTA, while it was reduced by about 27% during the potassium contracture induced in the EGTA solution. From these results, it is suggested that the calcium bound on the surface sites of the transverse tubular membrane and the sarcolemma can serve as a trigger for the release of calcium from the sarcoplasmic reticulum and can produce a resting potential and maintain relatively long duration excitability under the condition of extracellular calcium deficiency.     

The adenosine triphosphate (ATP) depletion test: comparison with the caffeine contracture test as a method of diagnosing malignant hyperthermia susceptibility

The adenosine triphosphate (ATP depletion ratio, which is the ratio [ATP] in skeletal muscle equilibrated with carbogen and 4% halothane for 30 minutes divided by [ATP] in skeletal muscle equilibrated with carbogen alone for 30 minutes is less than normal in most but not in all rigid MHS patients. The ratio is normal in non-rigid MHS patients. This diagnostic tool is, therefore, useful in the diagnosis of rigid MH. It is not, however, such a sensitive diagnostic parameter as the caffeine contracture test.     

Effects of the 5-HT2 receptor antagonist ritanserin on halothane-induced increase of inositol phosphates in porcine malignant hyperthermia

Recent studies have shown a significant increase of inositol phosphates (IPs) in skeletal muscle during episodes of halothane-induced malignant hyperthermia (MH) in pigs. After treatment with dantrolene and disappearance of MH crisis the IP concentrations returned to basal levels. In order to examine if the increase of IPs during halothane-induced MH may be related to an enhanced IP synthesis in response to activation of 5-HT2 (5-hydroxytryptamine) receptors, the effects of ritanserin, a selective 5-HT2 receptor antagonist, on IP levels were investigated. Biopsies of skeletal muscle of the hindlimbs were obtained in random order and IPs were determined in homozygous MH-susceptible (MHS) and MH-non-susceptible (MHN) swine in the following order: (1) basal, (2) after treatment with ritanserin (2.0 mg/kg), (3) after halothane challenge (3 vol% for 20 min). Basal concentrations of all IPs were higher in MHS than in MHN swine. Ritanserin did not cause any significant changes of IP levels compared to the basal concentrations in MHS and MHN pigs. In MHS pigs, ritanserin did not prevent a halothane-induced MH-crisis. After halothane challenge, 1,3,4-IP3, 1,3,4,6-IP4 and 1,3,4,5-IP4 levels were increased in MHS (during MH crisis) vs. basal concentrations, whereas no changes were found in MHN pigs. Since the increases of IP levels in MHS pigs during MH crisis found in the present study were comparable to those without pretreatment with ritanserin, shown by recent studies, it may be concluded that ritanserin does not prevent the increase of IPs during a halothane-induced MH. Thus, the present data indicate that increases of IP levels during halothane-induced MH in swine are due to other mechanisms than 5-HT mediated enhancement of IP synthesis.     

Regeneration of adrenal cortical tissue after adrenal autotransplantation

OBJECTIVE: This study examined the muscle fiber type distribution within the normal adult levator veli palatini muscle. METHODS: Levator veli palatini muscle tissue was harvested from the palates of 12 (seven female, five male) adult noncleft cadavers. Adjacent sections were stained for adenosine triphosphatase at pH 10.4 or 4.2. After mounting, magnifying, and photographing, Type I versus Type II fiber types were differentiated by the intensity of, or by the inhibition of, staining of matched fibers at each pH level. Type I fibers stained light at pH 10.4 and dark at pH 4.2, while Type II fibers stained light at pH 4.2 and dark at pH 10.4. MAIN OUTCOME MEASURES: The number of fibers counted for each specimen ranged from 60 to 616. The numbers of Type I and Type II stained fibers appearing in each muscle tissue sample were determined and expressed as a percentage of the total number of fibers identified. A few identified fibers could not be labelled as either Type I or Type II. RESULTS: The overall proportion of Type I fibers, averaged across all specimens, was 59.8%. Male specimens had 67.4% Type I fibers and 31.8% Type II fibers, while female specimens had 54.4% Type I fibers and 44.4% Type II fibers. CONCLUSIONS: Observed fiber type distributions were similar to those reported for other articulatory muscles, but differed slightly from previously reported distributions for normal levator veli palatini. The distributions observed in this study provide a baseline against which to relate fiber type data from the levator veli palatini of cleft palates to the functional status of the velopharyngeal mechanism.     

Definition of a diagnostic score of malignant hyperthermia using P-31 magnetic resonance spectroscopy

OBJECTIVES: To assess the metabolic muscular disorders associated with malignant hyperthermia (MH) using 31-P MRS, in order to develop a diagnostic tool for MH. STUDY DESIGN: Retrospective analysis of a series of case. PATIENTS: Group of 39 subjects, including 13 MH susceptible (MHS), and 26 not susceptible (MHN) members of recognized MHS families, according to the results of the in vitro contracture tests. METHODS: Each subject underwent two protocols, both including rest, exercise and recovery periods. Exercise was performed successively under aerobic and ischaemic conditions. RESULTS AND DISCUSSION: A significant early acidosis was recorded for the MHS group under both conditions of exercise (normoxia and ischaemia). However, the sensitivity of this parameter (77%) was not high enough to be considered as discriminant. Therefore a MRS score has been defined, corresponding to the sum of metabolic anomalies (acidosis, anomalies in PCr tum-over and in ATP or phosphomonoesters concentrations) recorded throughout both protocols. This score provided satisfactory results for both sensitivity (93%) and specificity (93%). CONCLUSION: 31-P MRS can act as a reliable diagnostic tool for MH.     

Effect of reactive oxygen species on K+ contractures in the rat diaphragm

Reactive oxygen species (ROS) are postulated to alter low-frequency contractility of the unfatigued and fatigued diaphragm. It has been proposed that ROS affect contractility through changes in membrane excitability and excitation-contraction coupling. If this hypothesis is true, then ROS should alter depolarization-dependent K+ contractures. Xanthine oxidase (0.01 U/ml) + hypoxanthine (1 mM) were used as a source of superoxide anion eliciting oxidative stress on diaphragm fiber bundles in vitro. Diaphragm fiber bundles from 4-mo-old Fischer 344 rats were extracted and immediately placed in Krebs solution bubbled with 95% O2-5% CO2. After 10 min of equilibration, a K+ contracture (Pre; 135 mM KCl) was induced. Fiber bundles were assigned to the following treatment groups: normal Krebs-Ringer (KR; Con) and the xanthine oxidase system (XO) in KR solution. After 15 min of treatment exposure, a second (Post) K+ contracture was elicited. Mean time-to-peak tension for contractures was significantly decreased in Post vs. Pre (16.0 +/- 0.7 vs. 19.8 +/- 1.0 s) with XO; no change was noted with Con. Furthermore, peak contracture tension was significantly higher (31.5%) in the XO group Post compared with Pre; again, no significant change was found with KR. The relaxation phase was also altered with XO but not with KR. Additional experiments were conducted with application of 1 mM hypoxanthine, with results similar to the Con group. We conclude that the application of ROS altered the dynamics of K+ contractures in the rat diaphragm, indicating changes in voltage-dependent excitation-contraction coupling.     

Reduced mechanical efficiency in chronic obstructive pulmonary disease but normal peak VO2 with small muscle mass exercise

We studied six patients with chronic obstructive pulmonary disease (COPD) (FEV1 = 1.1 +/- 0.2 L, 32% of predicted) and six age- and activity level-matched control subjects while performing both maximal bicycle exercise and single leg knee-extensor exercise. Arterial and femoral venous blood sampling, thermodilution blood flow measurements, and needle biopsies allowed the assessment of muscle oxygen supply, utilization, and structure. Maximal work rates and single leg VO2max (control subjects = 0.63 +/- 0.1; patients with COPD = 0.37 +/- 0.1 L/minute) were significantly greater in the control group during bicycle exercise. During knee-extensor exercise this difference in VO2max disappeared, whereas maximal work capacity was reduced (flywheel resistance: control subjects = 923 +/- 198; patients with COPD = 612 +/- 81 g) revealing a significantly reduced mechanical efficiency (work per unit oxygen consumed) with COPD. The patients had an elevated number of less efficient type II muscle fibers, whereas muscle fiber cross-sectional areas, capillarity, and mitochondrial volume density were not different between the groups. Therefore, although metabolic capacity per se is unchanged, fiber type differences associated with COPD may account for the reduced muscular mechanical efficiency that becomes clearly apparent during knee-extensor exercise, when muscle function is no longer overshadowed by the decrement in lung function.