An improved method of fixation for formalin-sensitive enzymes with special reference to myosin adenosine triphosphatase

Preferential skeletal muscle myosin loss in response to mechanical silencing in a novel rat intensive care unit model: underlying mechanisms

The muscle wasting and impaired muscle function in critically ill intensive care unit (ICU) patients delay recovery from the primary disease, and have debilitating consequences that can persist for years after hospital discharge. It is likely that, in addition to pernicious effects of the primary disease, the basic life support procedures of long-term ICU treatment contribute directly to the progressive impairment of muscle function. This study aims at improving our understanding of the mechanisms underlying muscle wasting in ICU patients by using a unique experimental rat ICU model where animals are mechanically ventilated, sedated and pharmacologically paralysed for duration varying between 6 h and 14 days. Results show that the ICU intervention induces a phenotype resembling the severe muscle wasting and paralysis associated with the acute quadriplegic myopathy (AQM) observed in ICU patients, i.e. a preferential loss of myosin, transcriptional down-regulation of myosin synthesis, muscle atrophy and a dramatic decrease in muscle fibre force generation capacity. Detailed analyses of protein degradation pathways show that the ubiquitin proteasome pathway is highly involved in this process. A sequential change in localisation of muscle-specific RING finger proteins 1/2 (MuRF1/2) observed during the experimental period is suggested to play an instrumental role in both transcriptional regulation and protein degradation. We propose that, for those critically ill patients who develop AQM, complete mechanical silencing, due to pharmacological paralysis or sedation, is a critical factor underlying the preferential loss of the molecular motor protein myosin that leads to impaired muscle function or persisting paralysis.

Slow fiber cluster pattern in pig longissimus thoracis muscle: implications for myogenesis

Recent evidence implicates fiber type proportions as playing a role in meat eating quality, and in pigs it has been suggested that the slow oxidative fibers contribute to both juiciness and tenderness. The fiber distribution in pigs is different from that found in most other species, in which the various types of skeletal muscle fiber are distributed in a "checkerboard" pattern, because in pigs the slow oxidative fibers have a clustered distribution. The initial processes leading to fiber clustering are likely to occur during myogenesis, but the precise mechanistic aetiology of this patterning and whether the slow oxidative fiber clusters occur in a random or ordered fashion is unknown. In the present study longissimus thoracis muscle from Large White crossbred pigs was sampled at the 10th rib, 48 h postmortem. Transverse cryo-sections were cut and histochemically stained to allow the identification of the main muscle fiber types: slow oxidative, fast glycolytic, and fast oxidative glycolytic. Images of the sections were captured and analyzed using point processes and Voronoi Tesselations to examine the randomness and spatial distribution of the clusters of slow oxidative fibers found in pig longissimus thoracis muscle. The results showed that an assumption of complete spatial randomness can be rejected and that a mathematical model incorporating a minimum distance of 1.7 to 2.0 microm between cluster centers produced fiber patterns similar to those observed in the original transverse sections of the muscle. In addition, if it assumed that the central fiber in each cluster is derived from primary myoblast progenitors, these results suggest that there may be some degree of repulsion between the primary fibers during the initial stages of cluster formation. The mechanistic basis of such repulsion is not clear, but it is speculated that secreted factors, such as sonic hedgehog or myostatin may play a role.

Masseteric hypertrophy?: preliminary report

We report radiological and histological investigations of a patient who presented with the masseteric hypertrophy. Sections of the patient's masseter muscles were also investigated using a series of histological techniques. The histological and morphometric analysis of the patient's masseter muscle showed numerous small fibres, which indicated that the masseteric enlargement was not the result of classic fibre hypertrophy. We suggest that the use of the term 'hypertrophy' in this condition may be misleading.

Partial transformation from fast to slow muscle fibers induced by deafferentation of capsaicin-sensitive muscle afferents

Mechanical and histochemical characteristics of the lateral gastrocnemius (LG) muscle of the rat were examined 21 days after capsaicin injection into the LG muscle. The capsaicin caused a decrease in generation rate of twitch and tetanic tension and an increase in fatigue resistance of LG muscle. The histochemical muscle fiber profile evaluated by myosin adenosine triphosphatase and reduced nicotinamide adenine dinucleotide tetrazolium reductase methods showed an increase of type I and IIC fibers and a decrease of the type IIB in whole muscle, and a decrease of the IIA, IIX fibers in the red part accompanied by their increase in the white part. Therefore the capsaicin treatment, which selectively eliminated fibers belonging to the III and IV groups of muscle afferents, induced muscle fiber transformation from fast contracting fatiguing fibers to slowly contracting nonfatiguing ones.

Enzyme-histochemical and morphological characteristics of fast- and slow-twitch skeletal muscle after brain infarction in the rat

The right middle cerebral artery was permanently occluded in 12-week-old male spontaneously hypertensive rats. After the surgery the rats were subjected to repeated behavioural tests during the observation period. Fourteen weeks after surgery the fast-twitch extensor digitorum longus (EDL) and the slow-twitch soleus muscle of both sides were removed and examined with regard to muscle fibre characteristics obtained by histochemical and morphometrical methods. Comparisons were made with age-matched controls. Limb placement and the ability to traverse a beam or a rotating pole were repeatedly tested 2-13 weeks after the operation. In spite of permanent sensorimotor deficits in limb placement and when traversing a rotating pole or beam, no increase in pathological changes was noted in either EDL or soleus. The number and proportion of fibre types remained unchanged in both muscles. There was no difference in muscle fibre size in either EDL or soleus. It is concluded that brain infarction in the rat, although causing marked impairment of contralateral motor function, does not have a major influence on the muscle-fibre morphology or fibre-type composition, irrespective of muscle type.

Osmotic diarrhoea and skeletal muscle protein synthesis in vivo

The pathogenic nature of the wasting seen in diarrhoea is unknown. This study measured protein synthesis in an established model of diarrhoea using lactose for seven days. Comparisons were also made with data obtained from rats fed an identical diet in which lactose was replaced by isocaloric glucose ad libitum (that is, the control diet). To account for diarrhoea induced anorexia, a third group of rats were included, which were fed identical amounts of the control diet as the rats with diarrhoea inducing diet. Comparisons of the diarrhoea induced group with rats fed the control diet ad libitum showed that diarrhoea caused a significant reduction in body weights. Type I and type II muscles showed significant reductions in protein, RNA, and DNA contents, as well as a fall in the derived parameters, RNA/DNA, protein/DNA, and RNA/protein. Fractional rates of protein synthesis (ks) were also reduced. However, synthesis rates of type I and II muscles relative to RNA (kRNA) were unchanged in these muscles in diarrhoea induced rats compared with ad libitum fed controls. In the jejunum there was an increase in the RNA/DNA ratio, and reductions in ks and kRNA. Comparisons were also made between rats with diarrhoea and rats pair fed the control diet. There were no changes in total muscle protein, RNA or DNA contents. This suggests that an important feature of body wasting in diarrhoea is the element of anorexia, which induces severe metabolic changes. The comparison between rats with diarrhoea and the pair fed group showed that histological features of the plantaris were not overtly changed, though diarrhoea caused significant reductions in RNA/DNA, protein/DNA, ks, and kRNA. Similar changes were seen for the soleus; though the reduction in ks failed to attain statistical significance. In the jejunum a comparison of diarrhoea induced rats with pair fed controls, showed increases in the ratios of RNA/DNA and protein/DNA.

Analysis of the sternotrachealis muscle fibers in some Anseriformes: histochemistry and sex differences

Histochemical characteristics and sizes of the fibers of the sternotrachealis (ST) muscle have been investigated in some Anseriformes (mallard, Pekin duck, Muscovy duck, and goose) of both sexes. A sexual dimorphism has been shown in the muscle of the species examined. In the mallard and Pekin duck, the male ST muscle shows type IIIA fibers in addition to the type I, IIA, and IIB fibers observed also in the female. In the Muscovy duck, the male muscle has only type I and IIA fibers, whereas the female muscle presents type I fibers and both types IIA and IIB fibers. Moreover, the mean frequencies for each fiber type were significantly different between males and females. In the goose, both male and female muscles present only type I and IIA fibers. In all the species examined, the mean areas of each fiber type are significantly different between male and female, being always larger in the male muscles. The anatomical sexual dimorphism observed in the ST muscle is discussed in relation to function.

An immunohistochemical approach to the intrafusal fibers of extraocular muscle spindles in sheep, cow, and pig

Intrafusal muscle fibers of the extraocular muscles (EOMs) of the sheep, cow, and pig were studied histochemically and immunohistochemically. In sheep and cow spindles, three intrafusal fiber types, namely the bag1, bag2, and chain fibers, were identified by a combination of standard histochemical methods and immunohistochemical staining with antibodies selective for slow-tonic (antitonic ALD) and slow twitch (anti-I BA-D5) myosin. The bag1 and bag2 fibers appeared immunologically different on the basis of their differential reactivity with the two antisera. Anti-tonic ALD preferentially stained the bag1 fibers, whereas anti-I BA-D5 labeled the bag2 fibers. Chain fibers did not react with either antisera. In the pig EOM spindles, in general, one bag and some chain intrafusal fibers were identified. The bag fiber was labeled by anti-tonic ALD, but it did not react with the anti-I BA-D5. These findings point to the existence in pig EOM spindles of only one bag fiber antigenically similar to the bag1 fiber of the other species examined.

Influence of the interval between removal and freezing of muscle samples on muscle fibre size with special reference to sample size and fibre type

To study the influences of the interval between removal and freezing of a muscle sample on fibre size, rat hindlimb muscles (soleus and extensor digitorum longus, EDL) were cut into three or five pieces and frozen at different intervals, cross-sectioned, stained and analysed morphometrically. As in a previous study (Larsson & Skogsberg 1988), a pronounced interval-dependent change in soleus muscle fibre size was observed, the fibres in soleus muscle samples frozen immediately (within 15 s) being significantly (P less than 0.01-0.001) larger than those samples frozen 4 or 10 min after removal. However, the interval-dependent change was only noted in small muscle samples, i.e. those where the maximum muscle fibre length was 6.5 mm, while samples in which the fibres were approximately twice this length showed no change. In the slow-twitch soleus, type I fibres predominate, and type II fibres were often too few in one or more cross-sections in each animal to allow reliable measurements of fibre size. The fast-twitch EDL was therefore studied, and the results indicated an interval-dependent change in fibre size which was differentiated according to enzyme-histochemical type, i.e. there was a significant change in type I and IIA fibres but not in type IIB. It is concluded that the interval between removal and freezing of small muscle samples, as in percutaneous muscle biopsies in man, is of vital importance for fibre size, and that this interval should be at least 2-4 min.

Effects of denervation on enzyme-histochemical and morphometrical properties of the rat soleus muscle in relation to age

The soleus muscle of young adult (5 months), adult (10-11 months) and old (23 months) male Wistar rats was unilaterally denervated for a period of 3 weeks and studied with regard to enzyme-histochemical and morphometrical properties. Denervation caused a marked atrophy of all fibres, irrespective of age and enzyme-histochemical type. Fibres having myofibrillar ATPase staining characteristics intermediate to type I and type IIA fibres increased in number in all age groups and a reduction in the number/proportion of type I fibres was found in adult and old animals. These results indicate that a slow-to-fast shift in myofibrillar properties as a consequence of denervation, shown to occur in the soleus muscle of young animals, also takes place in old age. This supports the view that atrophic fibres with intermediate myofibrillar ATPase staining characteristics, and possibly also atrophic IIA fibres, seen in old soleus muscle could be type I fibres which have undergone a transformation in response to the age-related denervation process.

Effects of bovine pituitary growth hormone alone or in combination with the beta-agonist clenbuterol on muscle growth and composition in veal calves

Twenty-three British Friesian bull calves at approximately 7 d of age were allocated to one of four treatments: controls untreated (five calves), a group (Clen) given 1 mg clenbuterol/kg diet (five calves), a group (GH) given a daily subcutaneous injection of 3.5 mg bovine pituitary growth hormone (GH) (five calves) and a group (Clen + GH) given a combination of clenbuterol as in the Clen group with GH as in the GH group (seven calves). All calves were given milk-substitute at levels adjusted weekly according to metabolic live weight. The animals were slaughtered over the weight range 150-170 kg. Samples of semimembranosus and triceps muscles were excised at slaughter. Treatment with GH produced approximately a threefold increase in mean daily serum GH concentration. Calves given Clen + GH were heaviest at slaughter and the combined treatment produced a significantly higher (P less than 0.01) feed conversion ratio. Administration of clenbuterol either alone or in combination with GH increased the cross-sectional area of both fast twitch glycolytic (FG), and fast twitch oxidative glycolytic (FOG) fibres in both muscles. In contrast GH produced little change in fibre size in semimembranosus muscle, although FOG fibres in triceps were slightly larger than in controls. Neither Clen nor GH resulted in any change in fibre percentage frequency in either muscle. Treatments involving clenbuterol produced a significant decrease in muscle glycogen concentration. Muscles from all three treatment groups tended to show small increases in protein and RNA concentration compared with the controls. Muscles from animals treated with GH alone exhibited an increase in DNA concentration not seen in muscles from the two other treatment groups. Overall, the differential response to the two agents suggested that clenbuterol does not mediate its effects via the GH axis, and that an additive response in terms of protein anabolism may be achieved from the use of a combination of clenbuterol plus GH.

Quantitative and qualitative morphological properties of the soleus motor nerve and the L5 ventral root in young and old rats. Relation to the number of soleus muscle fibers

The motor nerve to the soleus muscle and the L5 ventral root from young adult (3-6 months) and old (20-25 months) male Wistar rats were studied with regard to total number of myelinated nerve fibres, calibre spectra of myelinated fibres and morphological properties. The soleus muscle was examined with respect to total number of muscle fibres. A significant decrease in the number of myelinated nerve fibres was found in the old soleus nerves, and was mainly confined to the large-diameter fibers. Similarly, there was a significant decrease in the number of large myelinated fibres in the L5 ventral roots of old animals. Morphological changes in old nerves and spinal roots consisted of axonal degeneration with areas devoid of myelinated nerve fibres, and also myelin sheath irregularities, including myelin splitting with myelin balloon formation, infolded myelin loops and myelin reduplication. The axonal degeneration was more pronounced in the peripheral nerves than in spinal roots. In conformity with other studies, the soleus muscle showed an age-related decrease in the number of muscle fibres. These findings indicate that the decrease in fibre number in old soleus muscle is associated with degenerative neuronal changes and loss of alpha-motoneurons.

Mitochondrial alpha-glycerol phosphate dehydrogenase activity in IIA fibres of the rat lateral gastrocnemius muscle; the effect of Ca2+ and ATP

Mitochondrial alpha-glycerol phosphate dehydrogenase is an important enzyme, but it is difficult to extract and purify. We have measured the activity of this enzyme in single type IIA skeletal muscle fibres under initial rate conditions by microdensitometry of the formazan reaction product. The Km (1.6 mM) for the substrate (L-alpha-glycerol phosphate) was lower than reported for the extracted enzyme. Further, at low substrate concentrations (3 mM), the enzyme was allosterically activated by free Ca2+ concentrations of 1 microM or greater, and half-maximal stimulation occurred at 0.3 microM free Ca2+. In the absence of Ca2+, there was negative cooperativity of substrate binding with a Hill constant of 0.57, but no cooperativity occurred in the presence of calcium. ATP (10 mM) inhibited enzyme activity in the presence of Ca2+ but not in its absence.

Fiber-type composition of nine rat muscles. I. Changes during the first year of life

There are few data available that describe the changes in fiber-type profiles with age in a range of muscles; thus fiber-type profiles and areas were determined in nine muscles of female rats from weaning to 1 yr. The results not only demonstrated the difference in fiber-type composition, size, and hence functional area in the various muscles examined but also illustrated the changes in these parameters with age. In particular, it was clear that two ends of a spectrum of fiber compositions are represented in the muscles studied: tensor fasciae latae, mainly fast-twitch glycolytic at one end and soleus (and adductor longus), mainly slow-twitch oxidative at the other; the remaining muscles were mostly dominated by fast-twitch fibers of a variety of metabolic types. Aging resulted in an increase in fiber area that was most dramatic in fast-twitch glycolytic fibers. Changes in fiber type with age were noted in all muscles, but the exact nature of the developmental changes appeared muscle specific.

Effects of ageing on enzyme-histochemical, morphometrical and contractile properties of the soleus muscle in the rat

Enzyme-histochemical, morphometrical and physiological properties were studied in the slow-twitch soleus muscle of male Wistar rats 2-25 months old. There was a clear age-related shift in the enzyme-histochemical profile of the muscle, resulting from transformation of fast-twitch muscle fibres to slow-twitch ones. This process occurred in younger animals up to the age of 7-8 months. At older ages there was a slight reduction in the total number of fibres and an increasing incidence of atrophic and angular fibres, indicating a denervation process. The tetanus force was reduced with age, but when it was related to the total muscle fibre cross-sectional area, no age-related difference was found. The contraction time was significantly altered only in 20-25-month-old animals, where it was prolonged, whereas the half-relaxation time showed a tendency towards prolongation throughout the entire age-span. Thus, the force-generating capacity of residual contractile material was not significantly affected by age and the age-associated decrease in the number of fast-twitch muscle fibres was not an important contributing factor to the decreased speed of contraction.

Rapid continuous monitoring of enzyme activity in tissue sections: experience with the M85A and Zeiss UMSP-30 systems

We have previously described methods for the continuous monitoring of formazan deposition in tissue sections with a system based on the Vickers M85A microdensitometer. However, this instrument only allows the monitoring of a single field in each section. We have now developed a new system based on the Zeiss UMSP-30 microspectrophotometer. This machine is entirely computer controlled and by virtue of its fast-scanning stage allows the rapid (less than 0.5 s) sequential monitoring of multiple fields (up to 35) in each section. Thus a number of cell types may be studied simultaneously and work which used to take a full working day with the M85A system now can be performed in 45 min. As with the M85A the Zeiss system has full capability for data analysis (i.e. calculation of initial velocity rates, etc.). We have found that continuous monitoring of tissue sections by microdensitometry is a precise, sensitive and biochemically valid method of studying enzyme activity within the cellular matrix.

The action of the beta-agonist clenbuterol on protein metabolism in innervated and denervated phasic muscles

1. Clenbuterol treatment in innervated and denervated phasic extensor digitorum longus, plantaris and gastrocnemius muscles from rats caused a significant increase in RNA and protein contents in all muscles except denervated extensor digitorum longus. 2. All muscles showed an increase in the fractional rate of protein synthesis (Ks) with clenbuterol, but the temporal response varied. 3. The data suggest that the effect of clenbuterol on protein metabolism in innervated muscles is muscle-type specific, and demonstrate the homology of response for denervated muscles.

Different intrafusal fiber composition of spindles in sheep and pig extraocular muscles

Histochemical profiles of intrafusal fibers have been examined in muscle spindles of extraocular muscles of sheep and pig. Results show that in the sheep the intrafusal content presents, in addition to chain fibers, at least one bag1 and one bag2 fiber, whereas in the pig almost all the spindles are one-bag-fiber [corrected] spindles.

Evidence that the hypertrophic action of clenbuterol on denervated rat muscle is not propranolol-sensitive

1. The effect of propranolol on the clenbuterol-induced protein anabolism in innervated and denervated soleus and plantaris muscles of the rat was studied. 2. The response to the beta-agonist, clenbuterol, in both innervated and denervated muscles, was not significantly inhibited by the beta-antagonist, propranolol. 3. The results provide further evidence to suggest that the action of clenbuterol on skeletal muscle protein accretion may not be directly mediated by beta-adrenoceptors.

Multivariate classification of histochemically stained human skeletal muscle fibres by the SIMCA method

The SIMCA (soft independent modelling of class analogy) method of pattern recognition has been used to classify four muscle fibre types: I, IIA, IIB and IIC. The samples were histochemically stained human skeletal sections from biopsy material. Disjoint (separate) class modelling gave information about variables, i.e., the combinations of alkaline, acidic and Ca2+-containing preincubation procedures with appropriate discrimination power, and showed satisfactory separation of the classes (fibre types). Two serial stained muscle sections represent a minimum for a proper classification of the four fibre groups. A comparison of biopsy samples from two different persons showed significant variation in the data structure between similar fibre types, probably caused by intermuscle variations. It is suggested that the introduction of computer-assisted classification by the application of such multivariate analytical techniques both facilitates the classification of muscle fibres and improves the precision and reliability of fibre typing.

Effects of chronic nicotine exposure on contractile enzyme-histochemical and biochemical properties of fast- and slow-twitch skeletal muscles in the rat

Nicotine-exposed and control rats were compared with respect to contractile, enzyme-histochemical and biochemical properties of fast- and slow-twitch skeletal muscles in order to elucidate the mechanisms underlying previously observed effects of tobacco smoking on skeletal muscle. The nicotine was administered in drinking water, since this approach has been shown to result in a plasma nicotine pattern similar to that seen in tobacco smokers. In a pilot study, fibre-type proportions and mitochondrial enzyme activities tended to change in the slow-twitch soleus muscle after 9 weeks of nicotine exposure in a way similar to that previously reported in tobacco smokers. In the present study, the duration of nicotine exposure was more prolonged (18 weeks) and the number of studied animals was increased. In this series neither contractile, enzyme-histochemical nor biochemical properties were affected by the nicotine exposure. It is thus concluded that prolonged nicotine exposure has no significant effect on the skeletal muscle characteristics studied, and that other aetiological agent(s) for the observed differences in such characteristics between smokers and non-smokers should be searched for.

Effects of the interval between removal and freezing of muscle biopsies on muscle fibre size

Measurements of cross-sectional fibre areas are often performed in routine histopathologic diagnosis in cases of suspected neuromuscular disease. The methodologic error in fibre area measurements in duplicate muscle biopsies is reported, however, to be high and an animal model was therefore designed in order to study the mechanisms underlying this. The cross-sectional fibre area in the right soleus muscle, cut into 5 pieces and frozen after different lengths of time, was compared with that in the left soleus, which was frozen at the in situ length. It was found that this area was 23 +/- 6% larger (P less than 0.001) than in the control muscle, when the muscle sample was frozen immediately after being taken, as a result of contraction of the specimen. However, when the interval between removal of the sample and freezing was 2 min or longer, the fibre size was similar to the control muscle, but the muscle samples were still contracted and the decrease in muscle fibre size at longer intervals were accordingly due to a decrease in muscle fibre volume. It is concluded that the interval between removal and freezing of the biopsy is of vital importance for the fibre size.

Effects of age on contractile and enzyme-histochemical properties of fast- and slow-twitch single motor units in the rat

1. Contractile, enzyme-histochemical and morphometrical properties of muscle fibres were studied in single motor units of tibialis anterior (t.a.) and soleus muscles in young (3-6 months) and old (20-24 months) male albino rats. The technique of measuring glycogen depletion as a marker of previous muscle contraction was used for direct correlation of enzyme-histochemical and contractile parameters within single motor units of the fast- and slow-twitch type. 2. In t.a., the fast-twitch motor units covered 18 +/- 9 and 22 +/- 16% (P = not significant, n.s.) of t.a. cross-sections, included 148 +/- 65 and 162 +/- 63 muscle fibres per unit (P = n.s.) and had a cross-sectional area of 0.50 +/- 0.32 and 0.44 +/- 0.22 mm2 (P = n.s.) in the young and old animals, respectively (means +/- S.D.). 3. In soleus, the slow-twitch motor units covered 53 +/- 11 and 71 +/- 12% (P = n.s.), included 55 +/- 10 and 83 +/- 13 muscle fibres per unit (P less than 0.01) and had a total cross-sectional area of 0.14 +/- 0.02 and 0.22 +/- 0.06 mm2 (P less than 0.01) in the young and the old animals, respectively. The calculated number of motor units in soleus accordingly decreased (P less than 0.01) from 49 +/- 10 in the young to 29 +/- 10 in the old animals resulting in a loss of muscle fibres and an increased innervation ratio in old age (mean +/- S.D.). 4. Clusters of more than three muscle fibres were rarely seen in any of the glycogen-depleted motor units in either the young or the old animals. However, in the slow-twitch motor units of old animals the muscle fibres were less randomly distributed within the motor unit territory (P less than 0.05), indicating a denervation-reinnervation process. 5. The contraction and half-relaxation times of the isometric twitch were significantly prolonged in old age. In 274 randomly isolated single motor units of t.a. the contraction time increased from 13 +/- 1 in young animals to 17 +/- 3 ms in old ones and the half-relaxation time from 12 +/- 2 to 16 +/- 5 ms (P less than 0.01 in both cases). In 236 randomly isolated soleus single motor units, the contraction and half-relaxation times increased (P less than 0.001) from 24 +/- 5 to 31 +/- 7 ms and from 26 +/- 8 to 35 +/- 9 ms, respectively (mean +/- S.D.).(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of the anabolic agent, clenbuterol, on overloaded rat skeletal muscle

The dietary administration of clenbuterol to young male rats has been shown to produce a muscle specific hypertrophic growth response. This paper demonstrates that the combined effect of drug treatment and hypertrophic stimulus induced by tenotomy produced an additive effect on muscle growth. This effect was demonstrated in terms of both muscle composition (protein and RNA) and fibre size.

Propranolol apparently separates the physical and compositional characteristics of muscle growth induced by clenbuterol

The effect of propranolol on clenbuterol-induced changes in muscle fibre size and protein content were studied. Propranolol did not inhibit the ability of clenbuterol to stimulate protein accretion but reduced the increase in muscle fibre size. The compositional and physical characteristics of clenbuterol-induced muscle growth thus appeared to be separated by propranolol.

Effects of age on enzyme-histochemical fibre spectra and contractile properties of fast- and slow-twitch skeletal muscles in the rat

Enzyme-histochemical fibre spectra and contractile properties were studied in fast-twitch (extensor digitorum longus (EDL) or tibialis anterior (TA)) and slow-twitch (soleus (S)) muscles of young adult (6 months) and old (20-24 months) male albino rats. It was found that ageing affected fibre size, fibre type proportions, and contractile properties of muscle tissue in both qualitative and quantitative terms and that these age-related alterations differed between fast- and slow-twitch muscles. In the fast-twitch TA and EDL, no differences were observed in either the total number of fibres, the cross-sectional area or the absolute and relative numbers of different muscle fibre types and subtypes between young adult and old animals. In the slow-twitch S, on the other hand, both the total number of muscle fibres and the average cross-sectional fibre area were smaller in the old animals. The fibre loss and fibre atrophy were most pronounced in type II fibres, especially type IIA. In TA, twitch force was higher and tetanus force was unaltered in the old as compared with the young adult animals, resulting in an increased twitch:tetanus ratio in old age. In S, on the other hand, both these forces were lower in the old animals and the twitch:tetanus ratio was accordingly unchanged with age. When the tetanus force was related to age-related differences in total muscle fibre cross-sectional area, no differences were found in the maximum force-generating capacity of maintained contractile material in either fast- or slow-twitch muscles between the two age groups. Probable mechanisms underlying the above alterations are discussed.

Inhibition and reversal of denervation-induced atrophy by the beta-agonist growth promoter, clenbuterol

Dietary administration of the growth promoter, clenbuterol, ameliorated denervation-induced atrophy in rat soleus muscles. In acutely denervated muscles the drug inhibited the appearance of atrophy, and in chronically denervated muscles the atrophy was almost fully reversed. Responses in slow twitch oxidative fibres were particularly marked.

A new histochemical method for magnesium actomyosin adenosine triphosphatase at physiological pH

A new lead-precipitation technique for demonstrating magnesium-activated actomyosin adenosine triphosphatase (ATPase) at physiological pH and electrolyte levels in fixed skeletal muscle sections is reported. This method is compared with standard acid- and alkali-denatured muscle stained for calcium myosin ATPase as well as calcium-formalin denatured and pyrophosphate-formalin denatured muscle also stained for calcium myosin ATPase. The technique was developed using hamster skeletal muscle; however, it has also been applied to human, rat, and cat muscle. The fiber-type staining intensities of the formalin-denatured magnesium actomyosin ATPase closely resemble those of the formalin-denatured calcium myosin ATPase in rodents, but intensities in Type 1 fibers are reversed relative to calcium myosin ATPase in human muscle. Cat muscle shows intermediate characteristics.

The effect of a growth promoting drug, clenbuterol, on fibre frequency and area in hind limb muscles from young male rats

The effect of dietary administration of clenbuterol on soleus and extensor digitorum longus muscles was studied after 4 and 21 days. Both muscles showed an increase in wet weight with no significant change in total fibre number. After 4 days fibre cross-sectional areas were increased in soleus, but not in extensor digitorum longus, and after 21 days there was a change in fibre frequencies in extensor digitorum longus but not soleus muscles.

Muscle necrosis caused by the sub-units of crotoxin

The effects of the basic (CB) and acidic (CA) subunits of crotoxin on rat skeletal muscle in vivo have been studied. CB caused muscle necrosis, with damage limited to an outer rim of muscle fibres in rat soleus. The inflammatory response was relatively small. CA was apparently inactive, but the effect of CB was potentiated if injected in combination with CA. Not only were more muscle fibres damaged, but the damage was more diffuse. There was no relationship between the number of muscle fibres damaged and the extent of the oedema (measured as increase in wet weight.

Morphological observations and rates of protein synthesis in rat muscles incubated in vitro

Isolated soleus and extensor digitorum longus muscles from small (40 or 70 g) rats developed a central and substantial (13-57%) loss of glycogen and alpha-glucan phosphorylase activity after incubation for up to 2 h in vitro. The central 'core' of the muscles showed a marked decrease in the rate of protein synthesis. It is suggested that during brief periods of incubation the central core of isolated rat muscles becomes hypoxic, and that consequently the viability of such muscles must be in question.

Histochemical fibre typing and ultrastructure of the small fibres in Duchenne muscular dystrophy

Fibre type differentiation was carried out on 20 biopsies from Duchenne Muscular Dystrophy (DMD) sufferers using the acid-preincubated reaction for myofibrillar ATPase. Fibres, classified as either type 1, type 2 or 2C, were counted and their minimum diameters (least fibre axis) measured. Particular attention was paid to the population of small fibres that becomes increasingly prominent with the increasing age of the patient. Type 1 fibres were always predominant in the fibre population as a whole. The numbers of type 2 fibres declined with the increasing age of the patients while the numbers of 2C fibres increased. All fibre types were represented in the population of small fibres and the ratio of the numbers of types 1:2:2C fibres was approximately 1:1:3. Ultrastructural examination of the small fibres showed them to be at varying stages of regeneration and differentiation. The continuous presence of regenerating fibres in DMD while the muscles are wasting implies that while regeneration can be initiated it becomes increasingly constrained or restricted as the disease progresses. The cause of this restriction and whether it is related to the basic genetic lesion is unknown. It is suggested that the accumulation of fibrous connective tissue interferes with growth, either directly, in the formation of pseudomyotendinous junctions, or indirectly, by reducing nutrient exchange with the vascular system.

An evaluation of enzyme histochemistry in the diagnosis of childhood rhabdomyosarcoma

Six rhabdomyosarcomas were assessed by means of a battery of enzyme histochemical methods. The reactions were compared with those of a small number of other tumours belonging to the small-cell tumour category. Four of the rhabdomyosarcomas were positive for myophosphorylase and acetylcholinesterase. Myoblasts were strongly reactive for adenosine triphosphatase at alkaline pH and after acid pre-incubation, whereas the small undifferentiated neoplastic cell of the four alveolar rhabdomyosarcomas showed also discernible cytoplasmic reaction, but only after acid pre-incubation. Other tumour categories revealed positive staining for adenosine triphosphatase with acid pre-incubation but the degree of reaction was minimal by comparison. Other enzyme reactions were variable and, generally, did not distinguish between different tumour categories. It is concluded that enzyme histochemistry has a potential role in the diagnostic evaluation of the small cell tumour and should be included in the growing list of special techniques that may assist the pathologist confronted with this problem.

Rat diaphragm: changes in muscle fiber type frequency with age

This study demonstrates age-related changes in fiber type, distribution, and diameter that suggest that the diaphragm does not attain a static pattern of fiber type in adults. Furthermore, the progressive increase in the FG fiber diameters may be of importance in the interpretation of physiologic and biochemical parameters measured in the diaphragm muscle of animals of different age groups.

Effect of zinc deficiency on muscle fibre type frequencies in the post-weanling rat

Male weanling rats were maintained on diets either deficient or adequate in zinc for a period of 4 weeks. The rats on the deficient diet showed a reduction in food intakes and growth. After 4 weeks both soleus muscles and the lateral portion of the diaphragm were studied histochemically to examine the relative frequencies of the fibre types. The soleus muscles of the deficient animals showed a significant change in the proportion of slow and fast fibres. The diaphragm muscles of the deficient animals had a significant increase in the proportion of fast-twitch oxidative glycolytic fibres and a significant decrease in fast-twitch glycolytic fibres compared with the controls. Stainable lipid increased in the diaphragm muscle of the deficient animals with respect to their pair-fed controls.

Fatal infantile mitochondrial myopathy due to cytochrome c oxidase deficiency

A case of cytochrome c oxidase deficiency primarily affecting skeletal muscle is described. The child was admitted at 4 weeks due to failure to thrive and examination at that time revealed weakness and hypotonia. His condition deteriorated until at 11 weeks respiratory arrest necessitated artificial ventilation and death occurred at 14 weeks. Biochemical investigation showed lactic acidaemia and generalised aminoaciduria. Histochemical examination of muscle obtained at biopsy showed strong reactions for some oxidative enzymes, but by contrast cytochrome c oxidase could not be detected. Cytochrome c oxidase activity was less than 5% of control values in an extract of fresh muscle. The reduced-minus oxidised absorption spectra of muscle mitochondrial fractions prepared from post-mortem tissue showed an absence of cytochrome aa3 and a partial deficiency of cytochrome b. Ultra-structural examination showed abnormal mitochondria with loss of cristae and an abnormal granular matrix. The family history suggests autosomal recessive inheritance.

Differentiation of fiber types in skeletal muscle from the sequential inactivation of myofibrillar actomyosin ATPase during acid preincubation

A method is described for identifying fiber types of skeletal muscle from several mammalian species on the basis of the sequential inactivation of myofibrillar actomyosin ATPase during acid preincubation. When this method is used in combination with the standard alkaline preincubation at least 5 types of fibers can be identified. Of these, 2 are type I fibers with those of the slow twitch soleus muscle being different from those that exist in mixed muscles. The 3 subtypes of type II fibers exist independent of their metabolic properties. The need for careful standardization of histochemical methods for the visualization of myofibrillar actomyosin ATPase and the implication of the existence of different fiber types in apparently homogeneous muscle for the preparation of antibodies used for immunocytochemical methods of fiber identification are discussed.

Histochemical properties and innervation pattern of fast and slow-tonic fibre types of the anterior latissimus dorsi muscle of the chick

The anterior latissimus dorsi muscle of the chick is largely composed of slow-tonic fibres but contains a few fast fibres defined by their acid-labile, alkali-stable myofibrillar ATPase activity. These fibres are referred to as alpha fibres. Differing from the slow-tonic (alpha' and beta') fibres which are multiply innervated with en grappe endings, the alpha (fast) fibres are innervated by typical en plaque endings. The innervation of thirty-two alpha fibres were studied closely and it was concluded that about a half of the alpha fibres were focally innervated whereas a half were innervated in two distinct loci by en plaque endings. In only one case, a fast fibre with three widely spaced en plaque endings was observed. The mean intersynaptic length was significantly larger on alpha fibres than on alpha' and beta' fibres. No variation in the histochemical properties of myofibrillar ATPase was observed either along the entire length of singly and dually innervated alpha fibres, or along alpha' and beta' fibres. It is concluded that the three extrafusal fibre types of the anterior latissimus dorsi muscle maintain uniform histochemical characteristics along their length in spite of a possible innervation by several motoneurons.

Myotoxic activity of the crude venom and the principal neurotoxin, taipoxin, of the Australian taipan, Oxyuranus scutellatus

1 The crude venom of the Australian taipan. Oxyuranus scutellatus and its principal neurotoxin, taipoxin, were injected into the anterolateral aspect of one hind limb of the rat. 2 The effects of the venom and toxin on the morphology and physiology on the underlying soleus muscles were examined. 3 Both the crude venom and the toxin caused necrosis and degeneration of the muscle. Damage to the peripheral muscle fibres could be seen at the light microscopic level as early as 3 h after injection of the toxic compounds. 4 The necrotic response was accompanied by an infiltration of phagocytic cells and an extensive oedema. The wet weight of the damaged muscles was almost doubled by 6 h. 5 In individual muscle fibres, necrosis was associated with the disruption of the plasma membrane and the disorganization of the myofibrils. The basal lamina of the muscle fibres was left intact. 6 Denervated mammalian muscles and innervated avian muscles were also destroyed by tiapoxin, but immature avian muscle growing in tissue culture was resistant. 7 Of the 3 subunits of taipoxin, only the basic alpha-taipoxin was itself myotoxic. However, its potency was enhanced by the presence of the acid gamma subunit. The role of the neutral beta-subunit is unclear. 8 The period of necrosis and degeneration lasted for approximately 48 h, after which the muscle fibres began to regenerate. Regeneration took place within the surviving basal lamina, with the formation of myotubes by three days, and small, immature muscle fibres by five days. Regeneration was virtually complete by 21 days.

Effects of dexamethasone on fibre subtypes in rat muscle

The extent to which dexamethasone treatment produced atrophy of fast-twitch (EDL) and slow-twitch (SOL) muscles in rat was investigated. The mean weight of steroid-treated EDL muscles was decreased as compared to normal, whereas SOL muscles from normal and dexamethasone-treated animals showed no significant difference. Muscle fibre diameters also showed comparatively minor changes in SOL, which consists of Type 1 (slow oxidative) and Type 2A (fast oxidative/glycolytic) fibres. Rat EDL contains, in addition to Type 1 and Type 2A fibres, two sub-populations of fast glycolytic fibres (Types 2B and 2B'). These fibre types showed the most severe degree of atrophy both after dexamethasone treatment and after denervation. The mean ratio of the weights of denervated to innervated EDL muscles was lower in steroid-treated rats than in normal animals suggesting that the atrophy produced by steroid treatment in conjunction with denervation was more than simply additive. Analysis of the proportions of histochemical fibre types in SOL and EDL showed that dexamethasone treatment produced no major alterations in the fibre type constitution of these muscles. However, further histochemical studies showed that there was relatively severe impairment of myophosphorylase activity in Type 2B' (fast glycolytic) fibres as compared to other fibre types; conversely Type 1 fibres frequently contained increased myophosphorylase. Levels of beta-hydroxybutyrate dehydrogenase were low in both normal and steroid-treated EDL but high in SOL which also showed higher general oxidative activity. It is suggested that the particular susceptibility of fast glycolytic fibres to atrophy as a result of steroid treatment may be linked to: 1 the relatively severe reduction of myophosphorylase activity in these fibres and 2 their comparative inability to utilize alternative energy sources, especially substrates derived from free fatty acids.

Histochemical properties of the biventer cervicis muscle of the chick: a relationship between multiple innervation and slow-tonic fibre types

Chick biventer cervicis muscle fibres have been studied histochemically. Fast-twitch, focally innervated (alpha) fibres represent 70-80% of the total fibres in this muscles. Two histochemical profiles of slow-tonic multi-innervated (beta) fibres have been observed from embryonic life the adult (three-months) stage. These two slow-tonic types differ in the activity of their histochemically demonstrated myofibrillar ATPase after either acid or alkaline preincubation, and after formalin fixation. Both slow-tonic fibre types have a high oxidative metabolism and are PAS-negative. They are referred as to beta 1 and beta 2R fibre types (slow-tonic oxidative) in an expansion of Ashmore's nomenclature, and compared to avian slow-tonic sub-types that have been described in recent reports. beta 1 and beta 2 fibre types exhibit a similar pattern of innervation. Possible explanations of the origin of histochemical heterogeneity in multiple innervated fibres are discussed.

Histochemical differentiation of extrafusal muscle fibres of the anterior latissimus dorsi in the chick

Histochemical differentiation of the chick anterior latissimus dorsi (ALD) muscle was studied during embryonic development and after hatching. The two types of adult ALD tonic fibres (alpha' and beta') differentiate from a pool of acid and alkali-stable myofibrillar ATPase fibres. Intermediate stages of the transformation from beta' to alpha' were observed. At all developmental stages studied, a low percentage of formalin-resistant, alkali-stable and acid-labile ATPase fibres were observed. Such fibres have the histochemical properties of the alpha R or fast oxidative-glycolytic fibres and are assumed to be focally innervated.

A histochemical study of fibre types in rat extraocular muscles

The histochemical fibre type composition of the rat superior and medial rectus (SR and MR), superior oblique (SO) and levator palpebrae superioris (LPS) muscles was studied using the myofibrillar ATPase and NADH-tetrazolium reductase (NADH-TR) techniques. In the SR, MR and SO a peripheral zone containing small fibres and a central zone containing both small and large fibres could be identified. Four fibre types were present in the central zone of these muscles and were categorised as Type 1, Type 2a. Type 2a'. and Type 2b. Four fibre types were also identified in the peripheral zone--Type 1, Type 2a, Type 2a' and Type 2c. In the LPS Type 1, Type 2, Type 2a', Type 2b and Type 2c fibres were evenly intermixed without a zonal arrangement. The Type 1, Type 2a, Type 2b and Type 2c fibres correspond to accepted fibres types in the rat limb muscles. The type 2a' and Type 2a" fibres were differentiated from the Type 2a fibres on the basis of size and pattern and intensity of staining with the NADH-TR technique. The Type 2c fibres, which possess both acid-stable and alkali-stable myofibrillar ATPase, are considered to represent intermediate fibres in the process of transformation from Type 2 to Type 1, rather than fibres with a dual innervation as has been suggested in the past. The implications of these histochemical findings are considered in relationship to the physiology of individual motor units and to the function of the extraocular muscles.

Hypothyroid myopathy. A clinical and pathologaical study

Ten patients with varying degrees of hypothroid myopathy were studied clinically and by serial percutaneous needle muscle biopsies before and during treatment with L-thyroxine. The biochemical evidence of hypothyroidism was related to the severity of the myopathic and signs before treatment. The severity of myopathic symptoms before and during treatment correlated with the biochemical evidence of hypothyrodism, a type II fibre atrophy and increased central nuclear counts. Likewise, the clinical evidence of a myopathy before and during treatment was correlated with both a type II fibre atrophy and loss and increased central nuclear counts but was not related to the biochemical parameters of hypothyroidism, except the level of thyroid stimulating hormone. In the muscle, before and during treatment, of the two most severely affected patients, intracellular glycogen inclusions were seen in scattered muscle fibres. On light microscopy and on electronmicroscopy, numerous mitochondria were seen responding to L-thyroxine with accumulations of subsarcolemmal honey-combing. Vesicular abnormalities, an electron dense matrix or occasional crystalline deposits were seen in muscle mitochondria from less severely azffected patients. Severely myopathic muscle contained excessive glycogen, membrane bound glycogen and excess lipid in a mainly perinuclear distribution. Occasional myelin and membranous bodies were seen and satellite cells during the recovery phase. A group of patients with hypothyroid myopathy who are likely to have a delayed recovery of full muscle strength on L-thyroxine may be recognised by the presence of severe proximal muscle weakness and characteristic changes on histochemical and electronmicroscopic examination of muscle. The spectrum of histochemical and electronmicroscopic abnormalities of muscle revealed with increasing degree of hypothyrodism, suggests that a generally reversible acquired glycogen storage and mictochondrial disorder is an important feature in the pathogenesis of this condition.