D. R. Simpson

Muscle fibre type populations of human leg muscles.

SynopsisFour selected leg muscles (gastrocnemius, soleus, vastus lateralis and intermedius) from thirty-two humans were autopsied within 25 hr of death and examined histochemically. The results of histochemical myofibrillar adenosine triphosphatase activity demonstrated that the soleus and vastus intermedius muscles have a higher proportion of slow twitch fibres (70%, 47%) than their synergists, gastrocnemius and vastus lateralis, respectively. The gastrocnemius contains about 50% slow twitch fibres and the vastus lateralis about 32%. Similar proportions of slow and fast twitch fibres have been reported for these hindlimb muscles in other mammals. Human muscles, however, differ from other mammalian muscles in that the proportion of slow and fast twitch fibres were similar in the superficial and deep regions of the muscles examined. Fast twitch oxidative glycolytic fibres in sedentary humans were observed less frequently, and they are less prominent in terms of oxidative enzymatic activity when compared to similar fibres of several laboratory mammals studied previously.

THE INTERMEDIATE MUSCLE FIBER OF RATS AND GUINEA PIGS

The soleus, plantaris and gastrocnemius muscles of 60 Sprague-Dawley rats and 70 Hartley guinea pigs were studied histochemically. In the plantaris and gastrocnemius muscles, myosin adenosine triphosphatase activity differentiated intermediate fibers from red and white fibers as determined by malate dehydrogenase and succinate dehydrogenase and reduced nicotinamide adenine dinucleotide diaphorase activities. Contrary to what is commonly reported, red fibers could not be distinguished from white fibers on the basis of myosin adenosine triphosphatase activity as is commonly reported. The intermediate fiber was characterized by minimal menadione-mediated α-glycerophosphate dehydrogenase, phosphorylase and myosin adenosine triphosphatase activity and moderate malate dehydrogenase and succinate dehydrogenase and reduced nicotinamide adenine dinucleotide diaphorase activities. It is suggested that fibers with intermediate oxidative enzyme activity are physiologically slow, white fibers are fast and red fibers are moderately slow or even fast contracting fibers.

Properties of immobilized hind-limb muscles of the Galago senegalensis.

Abstract Morphological, biochemical, and physiological properties of longterm (6 mo) immobilized skeletal muscles of a nonhuman primate were studied in seven Galago senegalensis which were immobilized at the ankle and knee of one hind limb with an external brace. Electromyographic activity of the ipsilateral and contralateral quadriceps and muscles of the calf were assessed after 5 and 6 mo of immobilization. The EMG was markedly reduced in the immobilized muscles compared to the contralateral control when the brace was intact and the animal moving freely. Without exception, extensor muscles atrophied more than flexors. The soleus, a slow-twitch muscle atrophied more than any other muscle of the lower leg but the same was not true of the vastus intermedius the analogous muscle of the thigh. Slow-twitch oxidative fibers (SO) were atrophied more than fast-twitch oxidative glycolytic fibers (FOG), and FOG tended to atrophy more than fast-twitch glycolytic fibers (FG). The immobilized soleus and vastus intermedius had a smaller percentage of SO fibers than their controls, suggesting that they had faster contraction times. With respect to alterations in reduced nicotinamide adenine dinucleotide diaphorase activity, no consistent pattern was observed except for a greater coarseness of staining granules and more homogeneous dispersion of the granules throughout the cross-section of the fibers. No changes were found in phosphorylase, lactate dehydrogenase, or succinate dehydrogenase specific activity or in myoglobin concentration in homogenates of ankle flexors or the vastus lateralis. Myosin ATPase, but not actomyosin ATPase activity was significantly less in the immobilized gastrocnemius-plantaris muscles. No change in contractile properties related to speed were observed in the plantaris. This muscle did exert more twitch and tetanic tension per gram of muscle in the immobilized leg.

Work capacity, heart rate and blood lactate responses to iron treatment.

Summary. Changes in haemoglobin (Hb), work performance, heart rate and postexercise blood lactate were studied in iron deficient, anaemic subjects for 16 d following total dosage infusion of iron dextran, i.v. (30–50 ml). Six adult men and 14 women were subjects with initial Hb levels of 6.6±0.6 g/dl (mean±SEM) for the iron treatment group (n=10) and 8.0±0.7 for the placebo group (saline infusion, n=10). Serum iron levels were 0.51±0.15 and 0.67±0.12 mg/l for the two groups, respectively. Haemoglobin and maximal work time increased significantly within 4 d after iron treatment and continued to increase up to 16 d. No changes were found in the placebo subjects. Heart rates at a given exercise intensity were lower in the iron treatment group than in control subjects who had the same Hb levels but had not been treated with iron. Post‐exercise venous blood lactate was similar on succeeding days after iron treatement even though the subjects reached higher work loads.

Motor unit recruitment as reflected by muscle fibre glycogen loss in a prosimian (bushbaby) after running and jumping

A qualitative histochemical assessment of glycogen loss in biopsies was made in bush-babies after running and jumping. Glycogen loss was related to the specific type of exercise. After running, glycogen loss was greatest in the slow-twitch oxidative fibre and depletion in the fast-twitch oxidative glycolytic fibres was similarly greater than in the fast-twitch glycolytic fibres. After jumping, the opposite pattern of glycogen utilization occurred (FG>FOG>SO).

Overloaded skeletal muscles of a nonhuman primate (Galago senegalensis)

Abstract Selected morphological, biochemical, and physiological properties of skeletal muscles from five control and six trained adult nonhuman primates, Galago senegalensis , were studied. After a 6-month treadmill endurance-training program, fewer glycogen-depleted fibers were found in the plantaris of trained than in controls after 15 min of electrical stimulation. There was an increase in the proportion of fast-twitch oxidative-glycolytic fibers at the expense of fast-twitch glycolytic fibers, enhanced cytochrome a and c concentrations, and elevated SDH activity. No changes in glycolytic enzymes or contraction time of the normally fast-twitch plantaris muscle were found. Maximal twitch and tetanic muscle tension and overall fiber size were not significantly different in the controls and trained Galagos. However, fast-twitch oxidative-glycolytic fibers in the plantaris were significantly larger in the trained Galagos. These adaptations were muscle specific, demonstrating that muscles vary in response to treadmill exercise depending on anatomical location or action (or both) in the exercise as well as fiber-type composition.

Metabolic and contractile changes in fast and slow muscles of the cat after glucocorticoid-induced atrophy

Abstract The susceptibility of fast- and slow-twitch hind limb muscles to glucocorticoid-induced atrophy was investigated in adult male cats treated for 10 to 14 days with triamcinolone (4 mg/kg/day), using several histochemical, biochemical, and functional indices. After treatment, muscle weight loss in the fast-twitch muscles (medial gastrocnemius and vastus medialis) occurred to a greater extent than in the slow-twitch muscles (soleus and vastus intermedius), with the latter muscles decreasing in weight proportional to the body weight. Fast-twitch glycolytic (FG) fibers responded with similar degrees of atrophy in the muscles examined; however, slow-twitch oxidative (SO) and fast-twitch oxidative glycolytic (FOG) fibers atrophied more in the fast-twitch compared to the slow-twitch muscles. Phosphofructokinase and NADP+-linked isocitrate dehydrogenase specific activities decreased similarly in the fast-twitch muscles, while no change occurred in the slow-twitch muscles. Functionally, the soleus and medial gastrocnemius remained unchanged in abilities to generate tension tetanically, when this was expressed per unit muscle mass or per unit contractile protein. As a result of the treatment, however, the medial gastrocnemius fatigued faster in response to repetitive stimulation in the glucocorticoid-treated animals. The results suggest that the response of muscle to glucocorticoid-induced atrophy is not regulated by the primary metabolic pathways used for energy production. The differences in response of the SO and FOG fiber types in fast- versus slow-twitch muscles suggest basic differences in metabolic and activity profiles of the same fiber types in different muscles, which may influence susceptibility to atrophy.

Glucocorticoid-induced atrophy in different fibre types of selected rat jaw and hind-limb muscles

Six weeks of glucocorticoid treatment (triamcinolone-acetonide-21-phosphate, 1 mg/kg of body weight daily) resulted in a similar pattern of fibre type atrophy in jaw and hind-limb muscles. Fast-twitch glycolytic fibres were significantly atrophied in all muscles investigated. Fast-twitch oxidative glycolytic fibres were affected only in the fast (white) regions of the mixed muscles, while slow-twitch oxidative fibres were unaffected. The results from pair-fed controls (food intake matched to the glucocorticoid-treated animals) showed that the glucocorticoid produced an atrophic response in addition to that produced by the decreased food intake in the experimental animals. These results suggest that the jaw musculature shares the wasting effects induced by elevated circulating glucocorticoid levels often found in stress situations.

Response of muscle glycogen and phosphorylase to electrical stimulation in trained and nontrained guinea pigs

Abstract Total phosphorylase activity determined histochemically was selectively depleted in white fibers of the medial gastrocnemius of adult guinea pigs after 1 hour of electrical stimulation at a frequency of 5/sec. Histochemical depletion of phosphorylase was paralleled by glycogen depletion measured spectrophotometrically in homogenates and histochemically in frozen sections. Every phosphorylase-negative fiber was negative for glycogen as determined by the PAS stain. The number of PAS-negative fibers slightly exceeded the number of phosphorylase-negative fibers. No PAS- and 11 phosphorylase-negative fibers were found in nonstimulated muscles. The histochemical depletion of glycogen and of phosphorylase was more pronounced in the nontrained than in the trained animals.

Histochemical profiles of guinea-pig intrafusal fibres in normal muscles and after denervation, cordotomy and tenotomy

SynopsisHistochemical profiles of intrafusal fibres were analysed in normal muscles and in denervated, cordotomized and tenotomized preparations. Based on ATPase activity at polar regions, normal intrafusal fibres were classified as (I) ATPase-light fibres showing low or low-moderate activity when pre-incubated in either an acid or alkaline medium; (2) ATPase-dark fibres demonstrating high activity when preincubated in either an acid or alkaline medium and (3) ATPase-reversing fibres displaying low to moderate activity when pre-incubated in an acid medium, but showing high activity when pre-incubated in an alkaline medium. Four weeks after nerve section contrasting responses were seen between intrafusal fibre types. The ATPase-reversing fibres showed large decreases in polar cross-sectional area and NADH-diaphorase (NADH-D) activity, whereas fibres of the ATPase-light and ATPase-dark types were less subject to atrophy and their NADH-D levels were frequently increased. This differential effect suggests that ATPase-reversing fibres are trophically more dependent on neural innervation than ATPase-light and ATPase-dark fibres. After cordotomy and tenotomy no such marked differential responses were noted between fibre types.