Biochemical adaptation of mitochondria, muscle, and whole-animal respiration to endurance training

Uric acid and glutathione levels during short-term whole body cold exposure

Ten healthy subjects who swim regularly in ice-cold water during the winter (winter swimming), were evaluated before and after this short-term whole body exposure. A drastic decrease in plasma uric acid concentration was observed during and following the exposure to the cold stimulus. We hypothesize that the uric acid decrease can be caused by its consumption after formation of oxygen radicals. In addition, the erythrocytic level of oxidized glutathione and the ratio of oxidized glutathione/total glutathione also increased following cold exposure, which supports this hypothesis. Furthermore, the baseline concentration of reduced glutathione was increased and the concentration of oxidized glutathione was decreased in the erythrocytes of winter swimmers as compared to those of nonwinter swimmers. This can be viewed as an adaptation to repeated oxidative stress, and is postulated as mechanism for body hardening. Hardening is the exposure to a natural, e.g., thermal stimulus, resulting in an increased tolerance to stress, e.g., diseases. Exposure to repeated intensive short-term cold stimuli is often applied in hydrotherapy, which is used in physical medicine for hardening.

Metabolic adaptations to endurance training in older individuals

The purpose of this study was to describe the effects of moderate intensity exercise training on the muscle energy utilization, blood flow, and exercise performance of four sedentary older individuals (58 +/- 4 yrs). Subjects trained the dominant forearm each day for 12 weeks. The nondominant arm was not trained and served as a within-subject control. 31P nuclear magnetic resonance spectroscopy (31P NMRS) was used to identify the power output in watts (W) at the onset, or threshold, of intracellular acidosis (IT) in the exercising muscle during progressive exercise tests to fatigue. After 6 weeks of training, power output at the IT increased by 14% (p < 0.05) in the dominant arm; however, an additional 6 weeks of the same exercise program failed to produce a further increase in IT power. IT power of the nondominant forearm was not changed. In the dominant forearm, endurance time for a submaximal wrist flexion test was increased 34% and 58% at 6 and 12 weeks, respectively. Maximal voluntary strength was not affected by training, nor was resting or exercising blood flow. The training program delayed the onset of intracellular acidosis during progressive exercise and increased the capacity for submaximal work. These effects did not appear to depend on an increase in muscle blood flow.

Influence of exercise training on the oxidative capacity of rat abdominal muscles

Our purpose was to determine if endurance exercise training would increase the oxidative capacity of the abdominal expiratory muscles of the rat. Accordingly, 9 male rats were subjected to an endurance training protocol (1 h/day, 6 days/week, 9 weeks) and 9 litter-mates served as controls. Citrate synthase (CS) activity was used as an index of oxidative capacity, and was determined in the following muscles: soleus, plantaris, costal diaphragm, crural diaphragm, and in all four abdominal muscles: rectus abdominis, transversus abdominis, external oblique, and internal oblique. Compared to their non-trained litter-mates, the trained rats had higher peak whole body oxygen consumption rates (+ 16%) and CS activities in plantaris (+34%) and soleus (+36%) muscles. Thus, the training program caused substantial systemic and locomotor muscle adaptations. The CS activity of costal diaphragm was 20% greater in the trained animals, but no difference was observed in crural diaphragm. The CS activity in the abdominal muscles was less than one-half of that in locomotor and diaphragm muscles, and there were no significant changes with training except in the rectus abdominis where a 26% increase was observed. The increase in rectus abdominis CS activity may reflect its role in postural support and/or locomotion, as none of the primary expiratory pumping muscles adapted to the training protocol. The relatively low levels of CS activity in the abdominal muscles suggests that they are not recruited frequently at rest, and the lack of an increase with training indicates that these muscles do not contribute significantly to the increased ventilatory activity accompanying exercise in the rat.

Mitochondrial actaptations to chronic muscle use: Effect of iron deficiency

1. The effects of chronic muscle use on mitochondrial structure, enzymes and gene expression is reviewed. The role of iron deficiency in modulating this adaptation is discussed. 2. Chronic muscle use and disuse alter mitochondrial composition and affect mitochondrial subpopulations differentially. This has implications for an understanding of organelle assembly. 3. Iron deficiency decreases mitochondrial functional mass within muscle by reducing the level of heme and non-heme iron-containing components. This alters the metabolic response during exercise and results in a reduced endurance performance. 4. Both iron deficiency and chronic muscle use represent contrasting experimental models for the study of mitochondrial function and biogenesis.

Phosphorus-31 nuclear magnetic resonance study on the effects of endurance training in rat skeletal muscle

To evaluate changes in muscle energetics following endurance training, we measured phosphorus-31 nuclear magnetic resonance (31P NMR) spectra on rat muscle in vivo before and after training in the same animals. The endurance training lasted for 3 months. The 31P NMR spectra were obtained serially at rest, during exercise by electrical stimulation, and during recovery. Intramuscular phosphocreatine (PCr), inorganic phosphate (P(i)), adenosine 5'-triphosphate (ATP) and pH were determined from the NMR spectra. The ratio of PCr:(PCR + P(i) at rest showed no difference between the trained and control groups even after 3 months of training. During exercise, however, this ratio was significantly higher in the trained group than in the control group. The ratio also recovered more rapidly after exercise in the trained group. The intramuscular pH decreased slightly by approximately 0.1 pH unit during exercise but did not show a significant difference between the groups. These results indicated that endurance training of 3 months duration improved the ATP supply system in the muscle. They also demonstrated that 31P NMR is a potent method for evaluating the effects of training in the same individuals.

The effects of a reduced exercise duration taper programme on performance and muscle enzymes of endurance cyclists

The influence of tapering on the metabolic and performance parameters in endurance cyclists was investigated. Cyclists (n = 25) trained 5 days.week-1, 60 min.day-1, at 75-85% maximal oxygen consumption (VO2max) for 8 weeks and were then randomly assigned to a taper group: 4D (4 days; n = 7), 8D (8 days; n = 6), CON (control, 4 days rest; n = 6), NOTAPER (non-taper, continued training; n = 6). Muscle biopsy specimens taken before and after training and tapering were analysed for carnitine palmityltransferase (CPT), citrate synthase, beta-hydroxyacyl CoA dehydrogenase (HOAD), cytochrome oxidase (CYTOX), lactate dehydrogenase, glycogen and protein. Significant increases in VO2max (6%), a 60-min endurance cycle test (34.5%), oxidative enzymes (77-178%), glycogen (35%) and protein (34%) occurred following training. After the taper, HOAD and CPT decreased 25% (P less than 0.05) and 26% respectively, in the CON. Post-taper CYTOX values were different (P less than 0.05) for 4D and 8D compared with CON. Muscle glycogen levels were increased (P less than 0.05) after tapering in the 4D, 8D and CON, but decreased in NOTAPER. Similarly, power output at ventilation threshold was significantly increased in the 4D (27.4 W) and 8D (27 W) groups, but decreased (22 W) in the NOTAPER. These findings suggest that tapering elicited a physiological adaptation by altering oxidative enzymes and muscle glycogen levels. Such an adaptation may influence endurance cycling during a laboratory performance test.

The inhibitory effect of extracts of cigarette tar on electron transport of mitochondria and submitochondrial particles

Acetonitrile extracts of cigarette tar inhibit state 3 and state 4 respiration of intact mitochondria. Exposure of respiring submitochondrial particles to acetonitrile extracts of cigarette tar results in a dose-dependent inhibition of oxygen consumption and reduced nicotinamide adenine dinucleotide (NADH) oxidation. This inhibition was not due to a solvent effect since acetonitrile alone did not alter oxygen consumption or NADH oxidation. Intact mitochondria are less sensitive to extracts of tar than submitochondrial particles. The NADH-ubiquinone (Q) reductase complex is more sensitive to inhibition by tar extract than the succinate-Q reductase and cytochrome complexes. Nicotine or catechol did not inhibit respiration of intact mitochondria. Treatment of submitochondrial particles with cigarette tar results in the formation of hydroxyl radicals, detected by electron spin resonance (ESR) spin trapping. The ESR signal attributable to the hydroxyl radical spin adduct requires the presence of NADH and is completely abolished by catalase and to a lesser extent superoxide dismutase (SOD). Catalase and SOD did not protect the mitochondrial respiratory chain from inhibition by tar extract, indicating that the radicals detected by ESR spin trapping are not responsible for the inhibition of the electron transport. We propose that tar causes at least two effects: (1) Tar components interact with the electron transport chain and inhibit electron flow, and (2) tar components interact with the electron transport chain, ultimately to form hydroxyl radicals.

Exercise as a coronary protective factor

Exercise has multiple beneficial actions, both in normal subjects and in patients with coronary artery disease, which can be cardioprotective. Apart from reducing known risk factors and protecting against their deleterious effects, exercise also reduces the risk of coronary artery disease by increasing cardiovascular fitness. The exact contribution of each of these mechanisms in reducing coronary artery disease morbidity and mortality is unclear. Although fitness may be desirable, much of the cardioprotection can be achieved through increased leisure time and recreational physical activity. The risk-benefit ratio is very much in favor of moderate intensity exercise. Even in the absence of a controlled trial, the available evidence suggests that efforts to encourage physical activity are justified.

Muscle-specific regulation of the heme biosynthetic enzyme 5'-aminolevulinate synthase

The induction of 5'-aminolevulinate synthase (ALV synthase) activity in adult muscle by overload occurs in the absence of proportional changes in its mRNA content. Complete interpretation of these findings is difficult because little is known of the basal regulation of ALV synthase expression in muscle. In three adult chicken muscle fiber types (n = 5 each), differences in ALV synthase activity were correlated (r greater than or equal to 0.89; P less than 0.05) to the activities of cytochrome oxidase (COX) and citrate synthase (CS) and to levels of the "liver" isoform of ALV synthase mRNA. During posthatch development, ALV synthase activity and mRNA levels (n = 3-6 per time point) also covaried with changes in COX and CS activity. The highest levels of ALV synthase mRNA in muscle are observed early in myogenesis prior to induction of COX activity. The regulation of ALV synthase is also tissue-specific because the higher basal levels of ALV synthase activity in liver mitochondria are associated with disproportionately less oxidative enzyme activity and less of the liver ALV synthase isoform mRNA than in muscle.

Maintenance of structural and functional characteristics of skeletal-muscle mitochondria and sarcoplasmic-reticular membranes after chronic ethanol treatment

The effect of long-term ethanol intake on the structural and functional characteristics of rat skeletal-muscle mitochondria and sarcoplasmic reticulum was investigated. Functionally, skeletal-muscle mitochondria were characterized by a high respiratory control index and ADP/O ratio and a high State-3 respiration rate with different substrates. These parameters were not significantly different in preparations from control and ethanol-fed rats, except for a small increase in the rate of oxidation of alpha-oxoglutarate/malate in the latter. In submitochondrial particles from the two groups of animals there was no significant difference in cytochrome content, ATPase activity or the activity of respiratory-chain complexes. Mitochondrial membranes from untreated and ethanol-fed rats showed no difference in the baseline e.s.r. order parameter, and both preparations were equally sensitive to disordering by ethanol in vitro. Similarly, sarcoplasmic-reticulum preparations were not significantly affected by long-term ethanol feeding with respect to Ca2(+)-ATPase activity or in baseline order parameter and susceptibility to membrane disordering by ethanol in vitro. These membranes were also equally sensitive to degradation by exogenous phospholipase A2. Ethanol feeding did not alter the class composition of mitochondrial or sarcoplasmic-reticulum membrane phospholipids, nor the acyl composition of individual phospholipid classes. Specifically, the changes in acyl composition that characteristically occur in liver microsomal phosphatidylinositol and liver mitochondrial cardiolipin were not observed in the corresponding phospholipids from skeletal-muscle membranes. In experiments where membrane preparations from liver and skeletal muscle from the same ethanol-fed animals were compared, the liver membranes developed membrane tolerance, with the muscle membranes retaining normal sensitivity to disordering effects by ethanol. It is concluded that: (a) different tissues from the same animals differ in their susceptibility to ethanol; (b) the tissue-specific lack of development of membrane tolerance correlates with a lack of chemical changes in the phospholipids and with a retention of normal function of mitochondria and sarcoplasmic reticulum; (c) effects of chronic ethanol intake on muscle function are not due to a defect in the mitochondrial energy supply.

Exogenous glutathione increases endurance to muscle effort in mice

Many data suggest an involvement of toxic oxygen radicals in the termination of endurance to muscle fatigue. Being reduced glutathione (GSH), an efficient intracellular physiological antioxidant, experiments have been performed to discover whether exogenous GSH modifies endurance to exhaustive swimming in mice. GSH was administered to mice as a single dose (250, 500, 750 or 1000 mg/kg i.p.) or as repeated doses (250 mg/kg i.p. once a day during 7 days) 10 min before a swimming test to exhaustion. GSH 500, 750 and 1000 mg/kg, increased endurance to swimming by respectively 102.4%, 120.0% and 140.7%. GSH 250 mg/kg did not affect endurance when injected in a single dose but increased it by 103.7% when injected once a day for 7 days.

Muscle mitochondrial morphology, body composition, and energy expenditure in sedentary individuals

To investigate whether differences in metabolic rate are related to differences in muscle mitochondrial morphology and/or to differences in in vitro muscle respiration, we studied 17 healthy Caucasians, covering a wide range of body weight and composition [9 males, 8 females; body wt 96 +/- 37 (SD) kg; body fat = 28 +/- 10%]. Central and peripheral mitochondrial volume density (Vmit c and Vmit p, respectively) and the ratio of mitochondrial outer surface to volume of mitochondria (SVmit c in center and SVmit p at periphery) were determined by stereological analyses of transmission electron micrographs from samples of the vastus lateralis. There was no relationship between mitochondrial morphology or muscle respiration and 24-h energy expenditure, basal metabolic rate, or sleeping energy expenditure adjusted for differences in fat-free mass, fat mass, age, and sex. Although total body fat was not associated with muscle cell morphology, central distribution of body fat [waist-to-thigh circumference ratio (W/T)] correlated negatively with Vmit c (r = -0.58, P = 0.01), SVmit c (r = -0.59, P = 0.01), and SVmit p (r = -0.48, P = 0.05). W/T was also negatively related to muscle respiration (r = -0.59, P = 0.01). Despite the lack of relationship between metabolic rate and muscle mitochondrial morphology, central distribution of body fat is associated with lower mitochondrial density and larger mitochondria in skeletal muscle and is associated with a decreased oxidative capacity of muscle.

HSP70 and other possible heat shock or oxidative stress proteins are induced in skeletal muscle, heart, and liver during exercise

Exercise causes heat shock (muscle temperatures of up to 45 degrees C, core temperatures of up to 44 degrees C) and oxidative stress (generation of O2- and H2O2), and exercise training promotes mitochondrial biogenesis (2-3-fold increases in muscle mitochondria). The concentrations of at least 15 possible heat shock or oxidative stress proteins (including one with a molecular weight of 70 kDa) were increased, in skeletal muscle, heart, and liver, by exercise. Soleus, plantaris, and extensor digitorum longus (EDL) muscles exhibited differential protein synthetic responses ([3H]leucine incorporation) to heat shock and oxidative stress in vitro but five proteins (particularly a 70 kDa protein and a 106 kDa protein) were common to both stresses. HSP70 mRNA levels were next analyzed by Northern transfer, using a [32P]-labeled HSP70 cDNA probe. HSP70 mRNA levels were increased, in skeletal and cardiac muscle, by exercise and by both heat shock and oxidative stress. Skeletal muscle HSP70 mRNA levels peaked 30-60 min following exercise, and appeared to decline slowly towards control levels by 6 h postexercise. Two distinct HSP70 mRNA species were observed in cardiac muscle; a 2.3 kb mRNA which returned to control levels within 2-3 h postexercise, and a 3.5 kb mRNA species which remained at elevated concentrations for some 6 h postexercise. The induction of HSP70 appears to be a physiological response to the heat shock and oxidative stress of exercise. Exercise hyperthermia may actually cause oxidative stress since we also found that muscle mitochondria undergo progressive uncoupling and increased O2- generation with increasing temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)

Dehydroepiandrosterone and a beta-agonist, energy transducers, alter antioxidant enzyme systems: influence of chronic training and acute exercise in rats

We examined the influence of dehydroepiandrosterone (DHEA), a beta-agonist, and exercise training on enzymes that detoxify toxic oxygen species. Feeding 0.4% DHEA decreased hepatic cytosolic (c) selenium-dependent glutathione peroxidase (GPX), (-26%, P less than 0.0001) and increased hepatic mitochondrial (m) Mn superoxide dismutase (SOD), (+38%, P less than 0.001). DHEA decreased myocardial c-GPX (-21%, P less than 0.05) when compared to a beta-agonist (beta A; L644969 Merck and Co.) fed at 5 ppm but neither differed from the Control (C). In contrast, the beta A increased hepatic m-GPX (+25%, P less than 0.05). In skeletal muscle, DHEA and beta A decreased muscle c-GPX by 20 and 12%, respectively (P less than 0.0009). DHEA increased both muscle (+20%, P less than 0.01) and myocardial (+20%, P less than 0.05) c-glutathione S-transferase (GST) over beta A (+20%, P less than 0.01) but neither was significantly different from C. Similar to DHEA, chronic training (Tr) (1 h/day, 5 days/week at 27 m/min, 15% grade on treadmill) decreased hepatic c-GPX (-16%, P less than 0.003). Tr elevates muscle c-GPX (+36%, P less than 0.05) in C. Tr increased myocardial c-GPX by 28% in the beta A-treated rats, whereas Tr decreased myocardial c-GPX by 22% in the C (P less than 0.05, interaction). One hour of acute exercise (Ex) (70% VO2 max relative work load) decreased hepatic homogenate catalase (-12%, P less than 0.02) and increased hepatic m-Mn SOD (+28%, P less than 0.03). Ex decreased myocardial c-GST (P less than 0.05) only in the DHEA-treated rats. DHEA and Tr may improve efficiency of oxygen utilization at the tissue level with lower antioxidant enzyme activity in liver and locally protective up-regulation in muscle. beta A stresses oxygen utilization systems and liver responds by up-regulation of antioxidant enzymes. The increase in myocardial c-GPX activity in the beta A-treated group may be a protective effect against indirect catecholamine-induced myocardial necrosis which results from free radical generation.

The evolution of the scrotum: a new hypothesis

The adaptive significance of the scrotum is unresolved after more than 60 years of debate and experimentation. The "training hypothesis" introduced here suggests that testicular descent is a mechanism for improving sperm quality. The hypothesis proposes that: (1) testicular descent decreases blood supply to maturing sperm cells, (2) sperm mitochondria respond to the resulting oxygen stress by enhancing their enzymatic machinery for oxidative metabolism, as do oxygen-stressed muscle cell mitochondria, and (3) the resulting increase in aerobic fitness of sperm cells is advantageous in inter-ejaculate competition. The hypothesis suggests that there is a quantity-quality trade-off in sperm production, where taxa with internal testes produce large volumes of low-quality sperm while taxa with scrotal testes produce smaller volumes of higher-quality sperm.

Regulation of 5'-aminolevulinate synthase activity in overloaded skeletal muscle

The regulation of the mitochondrial enzyme 5'-aminolevulinate synthase (ALV synthase) activity during chronic weight-bearing activity (overload) in chicken skeletal muscle was investigated. Maximal enzyme activity was increased 2.5- and 4.0-fold after 3 and 7 days of overload. The content of ALV synthase mRNA (ng/mg total RNA) was not changed after 3 days but increased (20%; P less than 0.05) after 7 days of overload. Normalizing the content of ALV synthase mRNA relative to the increase in total RNA indicated that ALV synthase mRNA increased by 1.6- and 2.0-fold at 3 and 7 days, respectively. On this basis, the increase in enzyme activity per gram protein exceeded the increase in mRNA content per gram protein by 60-70%. During overload, the activity of cytochrome oxidase was unchanged after 3 days but increased by 1.5-fold (P less than 0.05) after 7 days of overload. The data indicate that 1) the initial rise in ALV synthase mRNA and activity due to overload occurs in the absence of a prior change in the level of cytochrome oxidase, an enzyme that requires heme for its assembly, and 2) induction of ALV synthase activity is regulated largely by processes at the translational or posttranslational steps.

ATP production rate in mitochondria isolated from microsamples of human muscle

Mitochondrial ATP production (MAPR) was determined using a bioluminescence method in mitochondrial preparations of human skeletal muscle. We obtained muscle samples from 21 healthy subjects using the percutaneous muscle biopsy technique. The subjects were grouped according to their degree of physical activity, i.e., from sedentary to highly active. The MAPR for each subject was related to the mitochondrial protein content and to the activity of glutamate dehydrogenase (GDH) estimated in muscle homogenates and in isolated mitochondria. With the use of GDH as a reference base, the MAPR could be expressed per muscle mass. MAPR was determined for different individual substrates and also for the combination of pyruvate, palmitoyl-carnitine, alpha-ketoglutarate, and malate (MAPRPPKM). The MAPR observed was higher for the combination of substrates than for any individual substrate tested. The relation between mitochondrial ATP production rate and GDH activity was the same for all subjects irrespective of physical activity status, but MAPRPPKM/kg muscle varied from 6.6 +/- 1.3 mmol.min-1.kg-1 in sedentary subjects to 11.0 +/- 2.2 in highly active subjects. The present method, which uses 50 mg of muscle tissue, enables mitochondrial function to be estimated in healthy subjects or patients with mitochondrial disorders.

Antioxidant enzymes and lipoperoxide in blood in patients with Kawasaki disease. Comparison with the changes in acute infections

Increased production of active oxygen species from activated neutrophils is postulated to contribute to endothelial damage in Kawasaki disease, leading to the formation of coronary aneurysms. To determine whether an altered oxidant-antioxidant balance exists in acute phase of Kawasaki disease, antioxidant enzymes in peripheral blood cells and plasma lipid peroxide were measured in patients. The two isoenzymes of intracellular superoxide dismutase were assayed by specific radioimmunoassays. Lipid peroxide in plasma and manganese superoxide dismutase in both polymorphs and lymphocytes were increased in the acute phase of Kawasaki disease. The erythrocyte glutathione peroxidase and catalase were also increased. On the other hand, copper zinc superoxide dismutase in polymorphs, lymphocytes and erythrocytes was unaltered. Acute infections did not appear to modify the levels of either antioxidant enzymes or lipid peroxide in blood. These results suggest that increased oxidative stress in Kawasaki disease evokes a reactive increase in antioxidant enzymes, and that this response in the defense system is related to the reversible nature of the tissue damage in most patients with Kawasaki disease.

A sensitive method for measuring ATP-formation in rat muscle mitochondria

A sensitive method for the measurement of the ATP production rate in isolated skeletal muscle mitochondria is presented. Mitochondrial suspensions were prepared by differential centrifugation from approximately 80 mg of soleus muscle. ATP production rates were measured luminometrically, utilizing a reagent based upon firefly luciferase, which emits light proportional to the ATP concentration. In a group of 10 rats the ATP production rates were measured with the following substrate combinations: pyruvate + malate, palmitoyl-L-carnitine + malate, alpha-ketoglutarate, succinate + rotenone and succinate alone. The variance of the method including tissue preparation, protein determination and the luminometric determination of ATP production was estimated to be 10-14% for the various substrates. Compared to values in the literature, the present results show a good agreement for the substrates pyruvate + malate and palmitoyl-L-carnitine + malate, but lower rates were obtained in our study for alpha-ketoglutarate and succinate + rotenone. The advantage of the luminometric method is its high sensitivity. Only 30-40 mg of tissue is required for a complete determination, compared to 1-2 g for a similar assay of oxygen consumption. The method is intended for use in human subjects and will facilitate studies of mitochondrial respiration both in patients of different age groups and in healthy subjects.

Oxidative muscular injury and its relevance to hyperthyroidism

In experimental hyperthyroidism, acceleration of lipid peroxidation occurs in heart and slow-oxidative muscles, suggesting the contribution of reactive oxygen species to the muscular injury caused by thyroid hormones. This article reviews various models of oxidative muscular injury and considers the relevance of the accompanying metabolic derangements to thyrotoxic myopathy and cardiomyopathy, which are the major complications of hyperthyroidism. The muscular injury models in which reactive oxygen species are supposed to play a role are ischemia/reperfusion syndrome, exercise-induced myopathy, heart and skeletal muscle diseases related to the nutritional deficiency of selenium and vitamin E and related disorders, and genetic muscular dystrophies. These models provide evidence that mitochondrial function and the glutathione-dependent antioxidant system are important for the maintenance of the structural and functional integrity of muscular tissues. Thyroid hormones have a profound effect on mitochondrial oxidative activity, synthesis and degradation of proteins and vitamin E, the sensitivity of the tissues to catecholamine, the differentiation of muscle fibers, and the levels of antioxidant enzymes. The large volume of circumstantial evidence presented here indicates that hyperthyroid muscular tissues undergo several biochemical changes that predispose them to free radical-mediated injury.

Muscle growth and exercise

This paper first reviews muscle growth and then considers the influence of exercise in growth. Knowledge about how muscle cells grow and some factors that may influence the growth pattern are discussed first since these effects must be considered before the influence of exercise becomes clear. Growth of muscle can occur in three ways: (1) by an increase in muscle cell numbers, (2) by an increase in muscle fiber diameter, and (3) by an increase in fiber length. All three of these mechanisms are involved in muscle growth. However, growth in cell numbers is limited to the prenatal and immediately postnatal period, with the animals and man being born with or soon reaching their full complement of muscle cells. Thus, growth occurs by either hypertrophy of the existing muscle fibers by adding additional myofibrils to increase the muscle mass or by adding new sarcomeres to the ends of the existing muscle fibers to increase their length. Both of these mechanisms occur during the growth process. Growth in the girth of the muscle fibers appears to take place by splitting of the myofibrils. This may be stimulated by development of stress creating an unequal pressure with splitting at the Z-band and development of additional SR and T-tubule systems. This adds to the diameter or girth of myofibers without any hyperplasia. The growth in length occurs at either end of the fibers and results in addition of new sarcomeres. In both cases, new myofibrillar protein must be synthesized and deposited in the muscle cells. It is suggested that adaptation by adding or removing sarcomeres is physiologically determined by the degree of force a muscle can generate that is in turn dependent on the degree of overlap of the thick and thin filaments. Thus, the amount of tension would control the number of in-series sarcomeres in a single muscle fiber. Nutrition is also known to play an important role in muscle and was discussed from the standpoint of the effects of nutritional adequacy and restriction. Although a nutritionally balanced and calorically adequate diet is required to achieve optimum muscle growth, it may be less efficient in terms of protein deposition than a moderately restricted diet. Muscle and bone deposition, however, can be limited on severely restricting the dietary intake. Although fat deposition is the first tissue to suffer on a severely restricted diet, muscle and bone follow next with the nervous system, brain and eyes being the last systems to be affected.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of high-intensity exercise on the respiratory capacity of skeletal muscle

The effect of high-intensity exercise on the respiratory capacity of skeletal muscle was studied in horses which ran five 600-m bouts on a track with 2 min of rest between exercise bouts, or once to fatigue on a treadmill at an intensity that elicited the maximal oxygen uptake. Venous blood and biopsy samples of the middle gluteal muscle were collected at rest, after each exercise bout, and 30 and 60 min post-exercise. Blood samples were analyzed for lactate concentration and pH and muscle samples for metabolites, pH, and respiratory capacity. Venous blood and muscle pH declined to 6.91 +/- 0.02 and 6.57 +/- 0.02, respectively, after the fifth track run and to 6.98 +/- 0.02 and 6.71 +/- 0.07, respectively, after treadmill running. Muscle metabolite changes were consistent with the metabolic response to high-intensity exercise. Muscle respiratory capacity declined greater than 20% (P less than 0.05) after a single exercise bout and was 45% of the control value after the fifth track run. Tissue respiration was depressed 60 min post-exercise but was normal 24 h later. These observations suggest that high-intensity exercise impairs the respiratory capacity of the working muscle. Although this occurred in parallel with reductions in pH, other factors could be responsible for this response.

Mitochondrial myopathies: clinical and biochemical features of 30 patients with major deletions of muscle mitochondrial DNA

Analysis of mitochondrial DNA (mtDNA) in muscle and blood from 72 patients with mitochondrial myopathy showed that 30 had major deletions of a variable proportion of muscle mtDNA. All of these 30 patients presented with progressive external ophthalmoplegia and limb weakness, and 8 had the additional features of the Kearns-Sayre syndrome. Of the 42 patients without detectable muscle mtDNA deletions, 10 had progressive external ophthalmoplegia and limb weakness, 2 had the Kearns-Sayre syndrome, 11 had limb weakness without extraocular involvement, and 19 had multisystem disorders predominantly affecting the central nervous system. Only 2 patients with mtDNA deletions had clinically affected relatives, compared with 10 of those without deletions. In the 4 patients with polarographic defects exclusively involving complex I (NADH coenzyme Q reductase), the deleted protein-coding genes were confined to those for complex I subunits. Thirteen other patients with apparently identical deletions had variable clinical and biochemical features. Immunoblots of complex I polypeptides from patients with deletions were either indistinguishable from controls or showed only a mild generalized decrease in all identifiable subunits.

The effect of detraining and reduced training on the physiological adaptations to aerobic exercise training

In previously sedentary individuals, regularly performed aerobic exercise results in significant improvements in exercise capacity. The development of peak exercise performance, as typified by competitive endurance athletes, is dependent upon several months to years of aerobic training. The physiological adaptations associated with these improvements in both maximal exercise performance, as reflected by increases in maximal oxygen uptake (VO2max), and submaximal exercise endurance include increases in both cardiovascular function and skeletal muscle oxidative capacity. Despite prolonged periods of aerobic training, reductions in maximal and submaximal exercise performance occur within weeks after the cessation of training. These losses in exercise performance coincide with declines in cardiovascular function and muscle metabolic potential. Significant reductions in VO2max have been reported to occur within 2 to 4 weeks of detraining. This initial rapid decline in VO2max is likely related to a corresponding fall in maximal cardiac output which, in turn, appears to be mediated by a reduced stroke volume with little or no change in maximal heart rate. A loss in blood volume appears to, at least partially, account for the decline in stroke volume and VO2max during the initial weeks of detraining, although changes in cardiac hypertrophy, total haemoglobin content, skeletal muscle capillarisation and temperature regulation have been suggested as possible mediating factors. When detraining continues beyond 2 to 4 weeks, further declines in VO2max appear to be a function of corresponding reductions in maximal arterial-venous (mixed) oxygen difference. Whether reductions in oxygen delivery to and/or extraction by working muscle regulates this progressive decline is not readily apparent. Changes in maximal oxygen delivery may result from decreases in total haemoglobin content and/or maximal muscle blood flow and vascular conductance. The declines in skeletal muscle oxidative enzyme activity observed with detraining are not causally linked to changes in VO2max but appear to be functionally related to the accelerated carbohydrate oxidation and lactate production observed during exercise at a given intensity. Alternatively, reductions in submaximal exercise performance may be related to changes in the mean transit time of blood flow through the active muscle and/or the thermoregulatory response (i.e. degree of thermal strain) to exercise. In contrast to the responses observed with detraining, currently available research indicates that the adaptations to aerobic training may be retained for at least several months when training is maintained at a reduced level. Reductions of one- to two-thirds in training frequency and/or duration do not significantly alter VO2max or submaximal endurance time provided the intensity of each exercise session is maintained.(ABSTRACT TRUNCATED AT 400 WORDS)

Training induced physiological and metabolic changes associated with improvements in running performance

The purpose of the present study was to examine the relationship between improvements in running performance and some of the prominent physiological and metabolic adaptations to endurance exercise training. Twelve male undergraduates agreed to participate in this study (trial group), aged matched physical education students provided a control group. Running performance, assessed as a five km time trial, improved from 19.69 +/- 2.24 to 19.22 +/- 2.03 min in the trial group (P less than 0.01) after training. Maximal oxygen uptake values increased from 56.0 +/- 6.1 to 60.7 +/- 5.4 ml.kg-1.min-1, the running speed equivalent to a blood lactate reference concentration of 4 mmol.l-1 (V-4 mM) increased from 3.79 +/- 0.77 to 4.04 +/- 0.71 m.s-1, and the rate of oxygen consumption at 3.58 m.s-1 (running economy) increased from 43.3 +/- 3.2 to 45.0 +/- 3.4 ml.kg-1.min-1 (P less than 0.01). The control group did not show any significant changes. The improved five km times in the trial group were significantly correlated (r = -0.71; P less than 0.01) with changes in the running economy rather than changes in the VO2 max (r = -0.07; ns), or V-4 mM (r = -0.13; ns) suggesting the increased rate of oxygen utilization reflected a greater oxidative degradation of metabolic substrates together with a slower rate of lactate production.

Enzymic and metabolic adaptations in the gastrocnemius, plantaris and soleus muscles of hypocaloric rats

1. The effect of hypocaloric feeding (25% of normal food intake for 21 days) of rats on the enzymic and metabolic adaptations in the gastrocnemius, plantaris and soleus muscles was studied. 2. In control and hypocaloric rats the muscle relaxation rates at 100 Hz were 35.76 and 11.38% force loss/10 ms respectively. Control rats exhibited enhanced force of muscle contraction as the frequency of stimulation increased from 10 to 100 Hz, with maximum force being at 100 Hz. Hypocaloric rats exhibited a decrease in the increment of force being exerted at high frequencies, with maintenance of force at lower stimulatory frequencies. 3. In muscles of hypocaloric rats, there were significant decreases in the maximal activities of hexokinase (17.6-37.0%), 6-phosphofructokinase (22.7-34.2%), pyruvate kinase (21.2-36.0%), citrate synthase (34.1-41.5%), oxoglutarate dehydrogenase (29.4-52.4%) and 3-hydroxyacyl-CoA dehydrogenase (26.7-32.1%), whereas the activities of glycogen phosphorylase increased (23.8-43.4%) compared with control values. 4. In soleus-muscle strip preparations of hypocaloric rats, there were significant decreases in the rates of lactate production (28.1%) and glucose oxidation (32.6%) compared with control preparations. 5. Mitochondrial preparations from muscles of hypocaloric rats incubated with various substrates exhibited decreased rates of oxygen uptake compared with control preparations. 6. In muscles of hypocaloric rats (gastrocnemius and soleus), there were significant decreases in the concentrations of glycogen (P less than 0.001) and phosphocreatine (P less than 0.001) and increases in those of pyruvate (P less than 0.001), lactate (P less than 0.001) and ADP (P less than 0.001), whereas those of ATP and AMP remained unchanged. 7. Calculated [lactate]/[pyruvate] and [ATP]/[ADP] ratios exhibited significant increases (P less than 0.05) and decreases (P less than 0.05) in muscles of hypocaloric rats respectively. 8. The results are discussed in relation to the genesis of muscle dysfunction caused by malnutrition.

Benzoyl peroxide interaction with mitochondria: inhibition of respiration and induction of rapid, large-amplitude swelling

When micromolar concentrations of benzoyl peroxide (BPO) are added to rat liver mitochondria, inhibition of mitochondrial NADH-oxidase and succinoxidase is observed. The addition of 2,4-dinitrophenol, an uncoupler of oxidative phosphorylation, results in only partial release of this inhibition, suggesting that BPO inhibits both electron and energy transfer in mitochondria. Release of inhibition is also observed when an electron donor, N,N,N',N'-tetramethyl-p-phenylenediamine, is added, suggesting that inhibition occurs on the substrate side of cytochrome c. When BPO is added to respiring submitochondrial particles, only reduced cytochrome b is observed to accumulate in the difference spectrum (reduced minus oxidized) in a manner analogous to that observed in the presence of antimycin A. These results indicate that BPO interacts at coupling site II between cytochromes b and c1. When respiring SMP are treated with BPO in the presence of the spin trap 5,5-dimethyl-1-pyrroline-N-oxide, electron spin resonance signals attributable to the hydroxyl and superoxide adducts are observed. Catalase and superoxide dismutase inhibit the formation of these adducts, suggesting the involvement of both hydrogen peroxide and superoxide radicals in this process. BPO also induces rapid, large-amplitude swelling of mitochondria; the swelling is dependent on the presence of monovalent cations but is independent of the presence of calcium, oxygen, and respiratory substrate. BPO-induced swelling appears to be disassociated from radical production and lipid peroxidation.

Oxidative capacity of muscle and mitochondria: correlation of physiological, biochemical, and morphometric characteristics

The oxidative capacity of cat skeletal muscles (soleus, gracilis, and gracilis chronically stimulated for 28 days) was derived from the total mitochondrial content in the muscle, the surface area of mitochondrial inner membranes, and respiratory activities of isolated mitochondria. Mitochondrial content was estimated by standard morphometry. The surface area of mitochondrial inner membranes per unit volume of mitochondria was estimated by a stereological method. The respiratory activities of isolated mitochondria were measured biochemically, using pyruvate/malate, glutamate/malate, succinate, or cytochrome c as substrate. Structurally and functionally, mitochondria from the three muscle types showed nearly identical characteristics. Oxidative activity was dependent on substrate; with succinate, 5.8 ml of O2 per min per ml of mitochondria was the rate most likely to represent physiological conditions. Oxidative activities of 3.1 ml.min-1.ml-1 with pyruvate/malate and 14.5 ml.min-1.ml-1 with cytochrome c as substrates were theoretical lower and upper bounds. The oxidative capacity of each of the three muscles was thus in direct proportion to the total volume of mitochondria in the muscle. The respiratory capacity of isolated mitochondria was very near to the maximal oxygen uptake rate of mitochondria that is commonly estimated in intact muscles of a wide variety of animals.

Effect of training on maximal oxygen uptake and aerobic capacity of locomotory muscles in tufted ducks, Aythya fuligula

1. The effects of artificial swim training on maximal oxygen consumption and heart rate, as well as on the capillarity and oxidative capacity of locomotory muscles, have been studied in the tufted duck, Aythya fuligula. 2. The artificial training programme resulted in a 27% increase in maximal oxygen consumption, mainly as a result of an increase in muscle capillarity (20% increase in capillary/fibre ratio). In addition, activity of an oxidative enzyme, citrate synthase, increased (by 42%) and there was a significant transformation of fibre types in the lateral gastrocnemius muscle. 3. Altering the duration and nature of the training stimulus, for example flying and diving, can bring about different degrees of muscular adaptation, particularly in oxidative capacity.

Enzymatic down regulation with exercise in rat skeletal muscle

Maximal activities of rat skeletal muscle mitochondrial citrate synthase (CS), malate dehydrogenase (MDH), and alanine aminotransferase (ALT), as well as several other mitochondrial enzymes involved in various metabolic functions were significantly suppressed after a single bout of acute or exhaustive treadmill running. This enzymatic "down regulation" was maintained 24 and 48 h post exhaustion, especially in the untrained rats. Neither muscle cytosolic nor hepatic enzymes exhibited down regulation after exercise. Proteolysis was increased with exercise as assessed by the clearance of [3H]leucine previously incorporated into the proteins of the rats. Decreased CS, MDH, and ALT activities correlated with a significant loss of mitochondrial total protein sulfhydryl (r = 0.67, 0.68, 0.59, respectively, P less than 0.001) in untrained rats and both CS and MDH could be partially restored by incubation with dithiothreitol. Endurance-tested untrained and trained rats had significantly higher glutathione peroxidase (GPX) activity in both muscle mitochondria and cytosol which correlated significantly with endurance time (r = 0.70 and 0.74, respectively). It is concluded that enzymatic down regulation is not caused by proteolysis alone; i.e., peroxides and oxygen free radicals produced in prolonged exercise may alter the intramitochondrial redox state by oxidizing free thiols that may be required at active sites of these enzymes. Training may enhance the ability of the muscle to resist the toxic oxygen species by increasing GPX activity.

Differential response of enzyme activities in rat diaphragm and intercostal muscles to exercise training

To determine whether respiratory muscles undergo alterations in enzyme activities of energy metabolism as a result of increased mechanical activity, adult male Wistar rats were subjected to a prolonged endurance training program. Analysis off maximal enzyme activity patterns in the diaphragm following 15 weeks of extreme training (final running duration: 210 min per day, 27 m.min-1 at 15 degrees grade, indicated significant reductions in the marker enzymes of the citric acid cycle (citrate synthase), glycolysis (pyruvate kinase, PK; lactate dehydrogenase, LDH), ketone body utilization (3-keto acid: CoA transferase) and transamination (glutamate pyruvate transaminase, GPT). No changes were found for the enzymes of glycogenolysis (phosphorylase, PHOSPH), glycolysis (glyceraldehyde phosphate dehydrogenase, GAPDH), glucose phosphorylation (hexokinase, HK) and beta-oxidation (3-hydroxyacyl: CoA dehydrogenase, HAD) following training. In contrast, in the external intercostal muscle, increases in the range of 57-77% were noted for the enzymes CS and HAD, whereas in the internal intercostal muscles no training induced alteration was evident for these enzymes. For both the intercostal muscles, a consistent trend was noted towards a reduction in all of the glycolytic enzymes investigated, however, significantly lower values were recorded for only PK and LDH in the internal intercostals. GPT was increased in the internal intercostal muscles. These findings indicate that the response pattern observed in the enzyme activities studied following training are to some degree specific to the respiratory muscle investigated.

Chronic administration of the oral hypoglycaemic agent diphenyleneiodonium to rats. An animal model of impaired oxidative phosphorylation (mitochondrial myopathy)

Daily subcutaneous administration of the oral hypoglycaemic agent, diphenyleneiodonium at a low dose (1.5 mg/kg body weight) over a 4-5 week period resulted in a normoglycaemic stable animal model of impaired oxidative phosphorylation in the rat. Diphenyleneiodonium specifically inhibits NAD-linked mitochondrial oxidation [Bloxham, Biochem. Soc. Trans. 7, 103 (1979)], and in isolated mitochondrial preparations from heart, soleus and gastrocnemius muscle and liver from treated animals NAD-linked respiration was reduced by 40% or more of mean control values. Brain and kidney mitochondria isolated from the treated group had similar rates of NAD-linked respiration to their respective control values. The activity of NADH-ferricyanide reductase was significantly reduced in all tissues tested, even in the isolated brain and kidney mitochondria where the activity in these tissues was 60-75% of control values. This suggests that at least 40% of Complex I activity must be inhibited before there is a decline in NAD-linked mitochondrial respiration. This paper discusses the use of diphenyleneiodonium as a means of establishing an animal model of the human disease state, termed mitochondrial myopathy.

Respiratory and cardiac responses to exercise-simulating peripheral perfusion in endurance trained and untrained rats. II. Temporal relationships between outflow parameters and cardiac and respiratory responses

In endurance trained (TR) and untrained (UTR) rats heart rate (HR) and respiratory rate (RR) were recorded during perfusion of the circulatorily isolated hind leg of the rat with exercise simulating modified tyrode solutions (TR:n = 10, UTR:n = 10; compare part I). During the 20 min test period and the preceding and succeeding periods of control perfusions with an unmodified tyrode solution, [lactate], pH, [K+], [Na+], PO2 and PCO2 were measured in the outflow of the femoral vein. In 3 experimental series: (1) hypoxic tyrode solution enriched with lactic acid (15 mmol.l-1), (2) normoxic solution with lactic acid, (3) hypoxic solution without lactic acid, were applied. The outflow parameters were cross correlated with both HR and RR. The analysis revealed a significant temporal relationship between [lactate], pH, PO2, PCO2 and [K+] and both HR and RR. In the trained rats no temporal correlation between either of the outflow and reflex parameters could be determined. This result was not due to low [lactate], but was also found during perfusion with lactic acid. In all 3 test conditions [lactate] in untrained individuals was best correlated with both HR and RR. Although the correlation peaks of the respiratory response, but not of the HR response were definitely lower in normoxic lactic and perfusion than in the two other experimental conditions, both inter- and intraindividual correlation analyses revealed a high degree of interdependence between respiratory and cardiac responses.

Is exhaustive training adequate preparation for endurance performance?

Our purpose was to test the significance of exhaustive training in aerobic or endurance capacity. The extent of adaptations to endurance training was evaluated by assessing the increase in physical performance capability and oxidative markers in the organs of rats trained by various exercise programs. Rats were trained by treadmill running 5 days.week-1 at 30 m.min-1 for 8 weeks by one of three protocols: T1-60 min.day-1; T2-120 min.day-1; and T3-120 min.day-1 (3 days.week-1) and to exhaustion (2 days.week-1). Groups T2 and T3 ran for longer than T1 in an endurance exercise test (P less than 0.05), in which the animals ran at 30 m.min-1 to exhaustion; no difference was observed between groups T2 and T3. All 3 trained groups showed a similar increase (20-27%) in the fast-twitch oxidative-glycolytic (FOG) fibers with a concomitant decrease in the fast-twitch glycolytic (FG) fiber population in gastrocnemius (p less than 0.05). The capillary supply in gastrocnemius increased with the duration of exercise (p less than 0.05): no difference was found between groups T2 and T3. Likewise, no distinction was seen between groups T2 and T3 in the increase in succinate dehydrogenase activity in gastrocnemius and the heart. These results suggest that the maximal adaptive response to endurance training does not require daily exhaustive exercise.

Respiratory and cardiac responses to exercise-simulating peripheral perfusion in endurance trained and untrained rats. I. Reflex responses and changes in perfusion outflow

Ventilatory and circulatory drives elicited by exercise-simulating perfusion of the circulatory isolated hindleg were examined in 10 trained (TR) and untrained (UTR) rats. TR were submitted to endurance training on a motordriven treadmill (30.min-1 at a grade of 10%, 5 days a week for 30 min). Exercise was simulated by perfusion with modified tyrode solutions: I.) hypoxic, enriched with lactic acid (15 mmol.l-1), II.) normoxic, enriched with lactic acid. III.) hypoxic without lactic acid. Perfusion was performed in anaesthetized animals through cannulae in the femoral artery and vein; the hindled was connected to the rest of the body only by nerve and bone. 10 min of control perfusion (normoxic tyrode solution) was followed by a 20 min test period and another 10 min control perfusion. Apart from heart rate (HR), respiratory rate (RR) and several outflow parameters were measured ([K+], [Na+], [lactate], pH, PO2, PCO2). During control period HR was slightly higher in UTR than in TR (375.5 +/- 3.9 (SE) vs. 364.1 +/- 5.5 beats/min-1, p less than 0.6 n.s.), and RR in UTR was significantly higher than those in TR (61.5 +/- 0.4 bpm vs. 55.5 +/- 3.9 breaths.min-1, p less than 0.001). During the test periods both HR and RR in UTR increased significantly while in TR they did not (e.g. in series I mean HR and RR in UTR increased by 8.9 +/- 1.2 beats.min-1 and 1.4 +/- 0.1 breaths.min-1 respectively, whereas in TR the changes were - 2.9 +/- 1.5 beats/min-1 and -0.8 +/- 0.2 breaths.min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of training on endurance and blood lactate concentration during submaximal exercise

The purpose of this study was to examine the effect of short-term training on maximum oxygen uptake (VO2 max) and two different measures of endurance performance. Endurance was determined for 15 female subjects (7 training, 8 control) as (1) exercise time to exhaustion at 80% VO2 max (T80%) and (2) the highest relative exercise intensity tolerable during a 30-minute test (T30 min), before and after a 6-week training period. In addition, VO2 max and the work rate equivalent to a blood lactate concentration of 4 mmol.l-1 (OBLA) were determined. Maximum oxygen uptake increased by 24% (p less than 0.01) for the training group (TG) and 7% (p less than 0.01) for the control group (CG). Cumulative average work rate (CAWR) during T30 min increased by 25% for the TG while there was no change for the CG. No significant difference was found pre- and post-training in the %VO2 max (estimated from CAWR) at which the TG and CG performed T30 min. Exercise time to exhaustion on T80% increased by 347% (p less than 0.01) and 16% (NS) for the TG and the CG respectively. Good correlations were found between VO2 max and CAWR (W) (pre-training r = 0.84; post-training r = 0.83), OBLA (W) and CAWR (W) (pre-training r = 0.89; post-training r = 0.88) and change in endurance time and the change in submaximal blood lactate concentration (r = 0.70, p less than 0.01). The results of this study suggest that the ability to sustain a high relative exercise intensity is not enhanced following short-term training.

Endurance training effects on striatal D2 dopamine receptor binding and striatal dopamine metabolite levels

We have previously shown that endurance training is associated with higher binding of [3H]spiperone to striatal D2 dopamine (DA) receptors of presenescent (21 months old) rats. In the present study we investigated the effects of 6 months of endurance training of young adults on the relationship between steady-state levels of DA and its metabolites in striatum and the affinity and density of striatal D2 DA receptors. The extent of training was confirmed by evaluating the maximal oxygen consumption (VO2 max) in the subjects. D2 DA binding was significantly increased at each of 3 [3H]spiperone concentrations in the young runners. A 'synaptic coupling ratio' calculated as the specific DA binding/DOPAC concentration was significantly increased in runners for the 0.1 and 0.4 nM radioligand concentrations. Across experimental groups levels of DA were highly and positively correlated with specific DA binding at the 0.1, 0.2 and 0.4 nM [3H]spiperone concentrations. Together, these results suggest that exercise can alter the number of DA binding sites and the metabolism of DA in young adult animals.

Iron deficiency in the elderly

Iron deficiency in the elderly almost always results from blood loss. The loss of iron can be viewed as occurring in four stages, which are reflected in the different tests used to diagnose iron deficiency. Tests used to diagnose iron deficiency have certain limitations regarding their ability to detect iron deficiency before the overt anaemia occurs. The tests which diagnose iron deficiency most accurately are low serum ferritin and reduced iron staining of a bone marrow aspirate. Because iron is present in many metabolic processes besides the production of haemoglobin, iron deficiency results in a variety of defects which are manifested at biochemical, tissue, and functional levels. Iron is a component of several enzymes in the respiratory electron transport chain. Adequate haem and iron levels are necessary to control cytoplasmic and mitochondrial protein synthesis. Iron deficiency results in tissue defects, including those affecting the gastrointestinal tract, and defects of mitochondria and lymphocytes. Normal iron levels seem to be necessary for normal work capacity. A deficiency of iron, independent of the anaemia, results in reduced exercise capacity that can be measured in both physiological and economic terms. Elderly patients complaining of increased fatigue should therefore be screened for iron deficiency. There is evidence to suggest that iron deficiency may predispose individuals to certain infections. Other information points to the promotion of certain bacterial and parasitic infections after rapid correction of iron deficiency. Thus elderly patients having iron replacement therapy should be followed closely. A deficiency of iron has been shown to result in certain behavioural and learning abnormalities. Iron deficiency has been shown to result in impaired control of body temperature, resulting in an increase in catecholamine levels. The impairment in heat-generating ability was shown to result from reduced conversion of T4 to T3 in the peripheral tissues.

Effects of endurance training on a mitochondrial reticulum in limb skeletal muscle

High voltage electron microscopy at 1500 kV, was used to examine the effects of endurance training on mitochondrial morphology in rat skeletal muscle. The soleus, deep portions of the vastus lateralis, and superficial portions of the vastus lateralis muscles were examined to represent slow-twitch-oxidative, fast-twitch-oxidative-glycolytic, and fast-twitch-glycolytic skeletal muscle fiber types, respectively. Muscle samples were removed from endurance trained and untrained control female Wistar rats (n = 6, each group). Tissues were fixed using standard electron microscopic techniques and sectioned transversely with respect to muscle fiber orientation to approximately, 0.5 micron thickness. The sections were stained on grids with uranyl acetate and Reynolds' lead citrate. Results confirmed the presence of a mitochondrial reticulum in all three skeletal muscle fiber types of both groups. Stereologic analyses indicated volume densities of intermyofibrillar mitochondria increased significantly (P less than 0.05) with endurance training in the three skeletal muscle fiber types. Surface-to-volume ratio of mitochondria was significantly decreased (P less than 0.05) after training only in the deep portion of the vastus lateralis muscle. It was concluded that the mitochondria in mammalian limb skeletal muscle are a reticulum which adapts to endurance training by proliferating.

Relationship between mitochondria and oxygen consumption in isolated cat muscles

1. Oxygen consumption, mitochondrial content and composition, intracellular lipid stores and fibre size were studied in isolated cat muscles: predominantly glycolytic gracilis, purely oxidative soleus and gracilis transformed into an oxidative muscle by chronic low-frequency (10 Hz) electrical stimulation. 2. Oxygen consumption in control gracilis at rest (0.303 +/- 0.050 ml O2 min-1 100 g-1; mean +/- S.E. of mean) was three to five times lower than in either stimulated gracilis (1.16 +/- 0.40) or soleus (1.57 +/- 0.56); it was about two times lower during maximal contractions in control gracilis (5.15 +/- 0.24) than in either stimulated gracilis (11.6 +/- 2.0) or soleus (9.34 +/- 0.78). 3. The volume density of mitochondria in control gracilis (2.75 +/- 0.12%) was half that of soleus (6.23 +/- 0.76) and only one-third that of stimulated gracilis (8.35 +/- 0.71). Subsarcolemmal mitochondria represented a significantly smaller fraction of the total mitochondrial volume in control gracilis than in either soleus or stimulated gracilis. 4. The surface area of inner and outer mitochondrial membranes per unit volume of mitochondria ranged from 23.4 to 26.1 and from 14.0 to 16.5 m2 cm-3, respectively. Mean values of these variables were not significantly different among experimental groups. 5. The volume density of the intracellular lipid stores in control gracilis (0.232 +/- 0.041%) was one-fourth of that in stimulated gracilis (0.860 +/- 0.12) and one-fifth of that in soleus (1.17 +/- 0.27). 6. The fibre cross-sectional area was 1670 +/- 260 micron 2 in control gracilis, 2250 +/- 280 in stimulated gracilis and 2390 +/- 110 in soleus. The difference was statistically significant only between control gracilis and soleus. 7. There was a significant correlation between the volume density of mitochondria and maximal oxygen consumption for all three muscles combined. 8. It was found that mitochondrial structure was similar in muscles with different oxidative capacities and that equal amounts of mitochondria consumed equal amounts of oxygen under limiting conditions of maximal in vivo respiration.

Endurance training does not affect diaphragm mitochondrial respiration

We sought to determine if chronic endurance training would increase mitochondrial respiration or protein content in rat diaphragm muscle. To this end, 20 male Wistar rats were randomly assigned to control (C) or an 8-week endurance training (T) group, n = 10 per group. At the end of T, VO2 max was 13% greater in T (83.3 vs 73.8 ml X kg-1 X min-1) and peak max power output was 32% greater (2.63 vs 1.98 kg X m X min-1). Mitochondrial specific activities of pyruvate-malate and cytochrome oxidase (expressed per mg mitochondrial protein) in both plantaris and diaphragm were similar in C and T rats, as were ADP/O and respiratory control ratios. When expressed per gram wet weight, whole muscle homogenate oxygen uptake (pyruvate + malate) and cytochrome oxidase activity increased 36 and 23%, respectively (P less than 0.05) in plantaris from T rats but did not change in diaphragm. Control oxidative capacity and mitochondrial protein content in the diaphragm were ca. 2-fold those in control plantaris. Plantaris mitochondrial protein content increased ca. 50% with T while the diaphragm was unaffected. We conclude that: plantaris muscle oxidative capacity adapts to training by increasing mitochondrial protein content, since there was no evidence for functional improvement of existing mitochondria, and in the face of a substantial training effect in whole animal and plantaris, the T stimulus was not sufficient to induce mitochondrial protein changes in the diaphragm. This finding is the result of either a 'pre-adaptation' secondary to the diaphragm's high chronic activity, or a sub-threshold increase in diaphragm recruitment during the exercise conditions studied.