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Biomedical subjects

J Henriksson

Publications and source records attributed to J Henriksson.

At least 73 records · Page 4Linked to original sources
PubMed1992

The ethanol technique of monitoring local blood flow changes in rat skeletal muscle: implications for microdialysis.

We have investigated the feasibility of monitoring local skeletal muscle blood flow in the rat by including ethanol in the perfusion medium passing through a microdialysis probe placed in muscle tissue. Ethanol at 5, 55, or 1100 mM did not directly influence local muscle metabolism, as measured by dialysate glucose, lactate, and glycerol concentrations. The clearance of ethanol from the perfusion medium can be described by the outflow/inflow ratio ([ethanol]collected dialysate/[ethanol]infused perfusion medium), which was found to be similar (between 0.36 and 0.38) at all ethanol perfusion concentrations studied. With probes inserted in a flow-chamber, this ratio changed in a flow-dependent way in the external flow range of 5-20 microliters min-1. The ethanol outflow/inflow ratio in vivo was significantly (P less than 0.001) increased (to a maximum of 127 +/- 2.8% and 144 +/- 7.4% of the baseline, mean +/- SEM) when blood flow was reduced by either leg constriction or local vasopressin administration, and significantly (P less than 0.001) reduced (to 62 +/- 6.4% and 43 +/- 4.4% of baseline) with increases in blood flow during external heating or local 2-chloroadenosine administration, respectively. Dialysate glucose concentrations correlated negatively with the ethanol outflow/inflow ratio (P less than 0.01) and consequently decreased (to 46 +/- 7.6% and 56 +/- 5.6% of baseline) with constriction and vasopressin administration and increased (to 169 +/- 32.5% and 262 +/- 16.7% of baseline) following heating and 2-chloroadenosine administration. Dialysate lactate concentrations were significantly increased (approximately 2-fold, P less than 0.001) during all perturbations of blood flow. In conclusion, this technique makes it possible to monitor changes in skeletal muscle blood flow; however, methods of quantification remain to be established. The fact that blood flow changes were found to significantly affect interstitial glucose and lactate concentrations as revealed by microdialysis indicates that this information is critical in microdialysis experiments.

2-Chloroadenosine↗
PubMed1992

Effects of physical training on the metabolism of skeletal muscle.

With moderate training (30-60 min daily at 70-80% of VO2 max, 3-5 times weekly), the trained muscles display a 40-50% increase in the content of mitochondrial oxidative enzymes. Concomitantly, the total number of muscle capillaries may increase by 50%, whereas the content of glycolytic enzymes is not, or only marginally, affected. The oxidative enzyme increase, which occurs over 6-8 wk, is lost in 4-6 wk if training is stopped. This loss occurs faster than the decrease in muscle capillarization and in the whole-body VO2 max. Trained muscles of athletes have 3-4 times higher oxidative enzyme levels and two- to threefold more capillaries per muscle fiber than untrained muscle. Extensive endurance training results in an enhanced percentage of slow-twitch fibers, but the time course of this change is not known. More extensive changes are observed in chronically stimulated rabbit muscle. In this case, enzymes of oxidation display large increases (6- to 12-fold), whereas there is a decrease of 70-90% in enzymes of glycolysis, glycogenolysis, gluconeogenesis, and high-energy phosphate transfer. There is a normal training response in mitochondrial enzyme activities in individuals with insulin-dependent and non-insulin-dependent diabetes, but the ability to form new skeletal muscle capillaries in response to physical training may be deficient in insulin-dependent diabetes. Training-induced changes in the metabolic character of skeletal muscle leads to an increased reliance on fat metabolism during exercise, with a lowered blood lactate concentration and a sparing of muscle glycogen.

Animals↗
PubMed1991

Prior poliomyelitis-reduced capillary supply and metabolic enzyme content in hypertrophic slow-twitch (type I) muscle fibres.

Capillary supply and oxidative and glycolytic enzyme activities were determined in muscle biopsies from the tibialis anterior muscle in six prior polio patients and a control group. The polio patients, who had paresis and atrophy, but were able to walk normally by making maximal use of all remaining anterior tibial motor units, showed type I (slow-twitch) muscle fibre predominance with a mean (SD) of 98 (2%) type I fibres versus 81 (8)% in the controls (p less than 0.01) and muscle fibre hypertrophy, the average type I fibre cross-sectional area being 108% (p less than 0.005) larger than in the controls. The number of capillaries per muscle fibre was not significantly different from that in the control group, but with the increased muscle fibre area in the polio patients, the capillary density was significantly lower. The number of capillaries in contact with type I fibres relative to fibre area was 40% lower in the patients than in the controls (p less than 0.005). The levels of citrate synthase and phosphofructokinase were significantly lower (38% and 33%, respectively, p less than 0.05) in the patients than in the controls, indicating decreased oxidative and glycolytic potentials in the muscle fibres of the polio patients. It is proposed that the abnormal high-frequency activation of all remaining motor units during each step cycle recorded in these patients constitutes a stimulus for type I muscle fibre predominance and hypertrophy but that the overall low muscle usage results in a decreased stimulation of capillary proliferation and mitochondrial enzyme synthesis. The low capillary density and decreased oxidative and glycolytic enzyme potentials might be important factors for the development of muscle weakness, fatigue and muscle pain, which are commonly occurring symptoms in patients with prior poliomyelitis.

Adult↗
PubMed1991

Hyaluronan in human skeletal muscle of lower extremity: concentration, distribution, and effect of exercise.

The concentration and localization of hyaluronan (HYA) were determined in biopsy specimens from resting human quadriceps femoris and anterior tibial muscles. The influence of physical exercise on HYA concentrations in the quadriceps femoris muscle and in blood was also evaluated. A sensitive radioassay was used for the quantification of HYA. The distribution of the glycosaminoglycan was demonstrated using a histochemical method that involved microwave-aided fixation and an HYA-binding protein. At rest, the muscle HYA concentration was 34.9 +/- 23.6 (SD) micrograms/g muscle wet wt with a large interindividual variation. Exercise had no significant effect on the muscle HYA concentration. The serum HYA concentration increased from 35.9 +/- 22.7 to 53.4 +/- 57.1 micrograms/l during exercise, but 30 min after the exercise the HYA concentration was significantly lower (19.1 +/- 6.3 micrograms/l) than the initial preexercise value. In resting skeletal muscles of the lower extremity, HYA was heterogeneously distributed in the perimysium and endomysium. Perivascular and perineural connective tissues were distinctly HYA positive.

Adult↗
PubMed1991

Effect of exercise on amino acid concentrations in skeletal muscle and plasma.

Protein is not normally an important energy fuel for exercising muscle. In spite of this, there is a significant increase in the rate of amino acid catabolism during exercise. This is secondary to the exercise-induced increase in several metabolic processes, such as hepatic gluconeogenesis and the citric acid cycle, where amino acid carbon is utilized. The suppression of protein synthesis during an exercise bout leaves amino acids available for catabolism. There is some evidence that basal amino acid concentrations in plasma and muscle may be higher in trained than in untrained individuals. In the rat, the concentration of free amino acids is higher in slow-twitch than in fast-twitch muscles. With short-term exercise, the transamination of glutamate by alanine aminotransferase leads to increased levels of alanine in muscle and plasma, and an increased release of alanine from the muscle. At the same time, the muscle and plasma glutamate concentrations are markedly decreased. The plasma glutamine level is elevated with short-term exercise, but changes in muscle glutamine concentration are more variable. With prolonged exercise, there is a depletion of the plasma amino acid pool, which may be explained by an increased consumption in organs other than muscle. With the exception of alanine, we found, however, that the muscle levels of free amino acids are kept stable throughout a 3.5-h exercise period. There is a significant activation of branched-chain amino acid metabolism with prolonged exercise, and the current data indicate that this is more pronounced in endurance-trained subjects than in untrained controls.

Amino Acids↗
PubMed1990

The possible role of skeletal muscle in the adaptation to periods of energy deficiency.

Skeletal muscle accounts for a large portion of the body's energy expenditure both at rest and during exercise. The present review focuses on some possible mechanisms for economizing energy in resting and contracting skeletal muscles, and on the available information about whether these mechanisms are important in the energy-deficient body. There is evidence, both in man and in the rat, that in a state of energy deficiency the size of slow-twitch fibres is better preserved than that of the fast-twitch fibres. Slow-twitch fibres have a lower activation threshold, and this seems to decrease their responsiveness to starvation. This would be advantageous as there is evidence that the energy expenditure per unit tension developed is lowest in slow-twitch fibres. There are reports of a slowing of malnourished muscle, but it is uncertain whether the starvation-induced hypothyroid state leads to some degree of fast-to-slow fibre transformation. Muscle glucose oxidation is depressed by starvation, mainly due to changes outside the muscle itself, but muscle enzymatic adaptations may also be important in this energy-saving process. In this respect, the higher capacity of the fatty acid oxidation and aerobic end-oxidation pathways in slow-twitch fibres tend to make them better adapted than fast-twitch fibres. Further muscle adaptations might include a decrease in BMR, possibly by reductions in protein turnover, ion pumping or futile cycling. The importance and costs of such potential adaptations should be evaluated by further research. This knowledge will be an important step in the further understanding of the pathophysiology of starvation.

Adaptation, Physiological↗
PubMed1989

Restoration of fast muscle characteristics following cessation of chronic stimulation: physiological, histochemical and metabolic changes during slow-to-fast transformation.

Implantable electronic stimulators were used to subject fast-twitch tibialis anterior and extensor digitorum longus muscles of adult rabbits to a chronically increased level of use. Stimulation was discontinued after 6 weeks and physiological, histochemical and biochemical properties of the muscles were examined at intervals over the ensuing 20 weeks. Previous work had shown that 6 weeks of stimulation was sufficient to bring about a substantial transformation of type in fast-twitch muscles, which then exhibited much of the character of muscles of the slow-twitch type. The present experiments showed that these stimulation-induced changes were completely reversible. The time-course of reversion was such that the muscles had recovered their original fast properties by about 12 weeks after the cessation of stimulation. The contractile characteristics and post-tetanic potentiation typical of fast muscle returned rapidly, in only 3-4 weeks, and over the same period the proportion of histochemical type 1 fibres declined from about 70% to control levels. Changes in fatigue-resistance, capillary density and enzyme activity followed a more prolonged time-course; in particular, the decline in the activity of enzymes of oxidative metabolism corresponded closely to that already established for the mitochondrial volume fraction. Reacquisition of fast properties was not accompanied by any changes in specific force-generating capacity. Observations from these experiments and from a related morphological study fit into a 'first-in, last-out' pattern for the response to stimulation and recovery. The slow-to-fast reversion that takes place during the recovery period provides a further opportunity for testing causal associations within the events underlying type transformation. It has important consequences for therapeutic applications that make use of the fatigue-resistant character of chronically stimulated muscle.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1989

In-vitro stimulation of the rat epitrochlearis muscle. I. Contractile activity per se affects myofibrillar protein degradation and amino acid metabolism.

The influence of contractile activity on protein degradation and amino acid metabolism in skeletal muscle was investigated by utilizing an in-vitro electrical stimulation model with the rat epitrochlearis muscle preparation. Graded decreases in contraction force and in the muscle content of ATP and PCr, and increases in lactate were recorded with different rates of stimulation (1 h) and with both isometric twitches and tetanic contractions. 3-Methylhistidine and phenylalanine were chosen as indicators of myofibrillar and total protein degradation, respectively. The release of 3-methylhistidine was significantly stimulated by contractile activity, but a significant increase in the total amount of this amino acid (released amount + tissue content) occurred only at the most intense contraction rates. The release rate, tissue content and total amount of phenylalanine were not influenced by the contractions. Glutamate formation was generally inhibited, but its release was increased. Alanine synthesis was increased in moderately and intensely stimulated muscles. Glutamine and glycine were not influenced by the contractions, however. Inhibition of protein synthesis did not significantly influence protein degradation or amino acid release. The data suggest that in the absence of anabolic factors in the medium, myofibrillar protein degradation is increased in heavily activated muscle. This takes place without total protein breakdown being affected.

Adenosine Triphosphate↗
PubMed1989

In-vitro stimulation on the rat epitrochlearis muscle. II. Effects of catecholamines and nutrients on protein degradation and amino acid metabolism.

The influence of catecholamines and branched-chain amino acids (BCAA) plus insulin on protein degradation and amino acid metabolism was investigated in isolated and electrically stimulated rat epitrochlearis muscles. 10(-7) M adrenaline significantly increased the total amount of muscle tyrosine during 40 min of stimulation with 50 Hz (I s min 1) pulse trains. On the other hand, BCAA + insulin at normal and five times normal plasma concentrations had no effect on muscle tyrosine. Muscle 3- methylhistidine was not influenced by any of the treatments. Muscle release and content of aspartate, alanine, glutamate and glutamine showed individual response characteristics to catecholamines and BCAA + insulin. The data indicate that adrenaline can induce an increased total protein degradation in rat fast muscle during acute contractions in vitro and, furthermore, that BCAA + insulin does not retard protein breakdown during acute muscle contraction.

Amino Acids↗
PubMed1989

Effects of adrenaline and prior exercise on the release of alanine, glutamine and glutamate from incubated rat skeletal muscle.

Catecholamines have been proposed as important regulators of the rate of amino acid release from skeletal muscle. In the present study, we have investigated the influence of adrenergic action and its possible interaction with exercise on muscle release and tissue content of alanine, glutamine and glutamate. For this purpose epitrochlearis muscles were dissected from resting and exercised (1 and 2 h) rats and incubated for 1 h in the presence or absence of adrenaline. In addition, muscles from water-immersed resting rats were included to separate the influence of the stress involved in the swimming exercise from that of muscle contractile activity per se. In muscles from untreated resting rats, the release, tissue content and total amount (released amount + tissue content) of the three amino acids were not influenced by 10(-7) M adrenaline; when the adrenaline concentration was raised to 10(-5) M only the tissue content of glutamate was significantly changed (-50%, P less than 0.001). However, in muscles of rats subjected to 2 h prior exercise or water immersion, 10(-7) M adrenaline significantly increased the release of glutamine (+ 48% and +34%, P less than 0.05) and glutamate (+38% and +27%, P less than 0.05). Moreover, 1 h of water immersion resulted in a significant increase in muscle glutamine and glutamate compared to values from the exercised and control rats. The data suggest that adrenergic action is involved in the regulation of muscle amino acid transport during exercise and that the stress involved in exercise may mask the influence of contractile activity per se on formation of amino acids in skeletal muscle.

Alanine↗
PubMed1989

Indirect effect of catecholamines on development of insulin resistance in skeletal muscle from diabetic rats.

The role of an increased sympathetic activation in the development of insulin resistance in diabetic skeletal muscle was investigated. Epitrochlearis muscles from rats with streptozocin-induced diabetes and from controls were incubated in vitro for 0.5-12.0 h. Diabetes decreased maximal insulin-stimulated (20 mU/ml) glucose transport capacity by 60% (P less than .001), but this decreased insulin responsiveness returned to normal on in vitro incubation (3.79 +/- 0.59 before vs. 8.92 +/- 0.64 mumol.ml-1.h-1 after 12 h of incubation). The reversal of decreased insulin responsiveness in diabetic muscles did not require the presence of insulin and was not affected by the presence of 5.0 x 10(-8) M of epinephrine. However, it was possible to partially prevent the development of insulin resistance with regard to glucose transport by treating the rats with the beta-adrenergic antagonist propranolol (0.5 mg/kg) every 12 h during the entire 72-h period in which the animals were kept diabetic (insulin responsiveness was 3.16 +/- 0.40 mumol.ml-1.h-1 for saline-injected group vs. 5.55 +/- 0.46 mumol.ml-1.h-1 for propranolol-treated group). This effect was not present after a single injection of the drug 2 h before the experiment or when propranolol treatment was withdrawn 12 h before the experiment. The beta-adrenergic blockade markedly reduced the plasma concentration of free fatty acids (0.5 +/- 0.01 mumol/ml for propranolol-treated rats vs. 1.1 +/- 0.1 mumol/ml for saline-treated rats; P less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1989

Chronic stimulation of mammalian muscle: enzyme and metabolic changes in individual fibres.

Earlier investigations involving chronic muscle stimulation have shown that skeletal muscle cells possess a much greater metabolic plasticity than had previously been recognized. We have described more fully the time course for the changes in different enzyme systems in single fibres of rabbit fast-twitch tibialis anterior (TA) muscles after periods of continuous stimulation of up to 10 weeks. After 2-5 wk every fibre shows higher levels of many oxidative enzymes than any control fibre; in some cases these levels are 2-10 times higher (well above any found even in the control soleus, a slow-twitch muscle). Citrate synthase, hexokinase and 3-oxoacid CoA-transferase are representatives of this group of enzymes. Other enzymes, such as malate dehydrogenase and amino acid aminotransferases also increase dramatically, but peak single fibre levels do not reach much above the highest in controls. These differential effects confirm at the single fibre level that chronic stimulation can alter mitochondrial composition. According to their staining reaction for myofibrillar ATPase, TA fibres are approximately 25% type IIA, and 75% type IIB, but by 5 wk these are converted to a mixture of type I, IIA and IIC fibres. At 5 wk, levels of glycolytic and high-energy phosphate transfer enzymes had decreased by 80% or more, and seemed to be adjusted to levels appropriate to their (new) ATPase type. This is in contrast to many enzymes of oxidative metabolism, which increase without synchronization with fibre type change. Determinations of metabolite concentrations in individual fibres from muscles freeze-clamped after varying periods of stimulation gave results which differ strikingly from data for acute stimulation. The findings reinforce our previous view that the high levels of ATP utilization engendered by chronic stimulation of muscle elicit a matching response in ATP production through a series of profound adaptations. Some of these are never encountered under the less extreme conditions of endurance exercise. Such features add to the interest and value of the chronic stimulation model as a means of studying the metabolic plasticity of muscle.

Adenosine Triphosphatases↗
PubMed1988

NADH content in type I and type II human muscle fibres after dynamic exercise.

The effect of dynamic exercise on the NADH content of human type I (slow-twitch) and II (fast-twitch) muscle fibres was investigated. Muscle biopsy samples were obtained from the quadriceps femoris of seven healthy subjects at rest and after bicycle exercise at 40, 75 and 100% of the maximal oxygen uptake [VO2(max.)]. At rest and after exercise at 100% VO2(max.), muscle NADH content was significantly higher (P less than 0.05) in type I than in type II fibres. After exercise at 40% VO2(max.), muscle NADH decreased in type I fibres (P less than 0.01), but was not significantly changed in type II fibres. After exercise at 75 and 100% VO2(max.), muscle NADH increased above the value at rest in both type I and II fibres (P less than 0.05). Muscle lactate was unchanged at 40% VO2(max.), but increased 20- and 60-fold after exercise at 75 and 100% VO2(max.) respectively. The finding that NADH decreased only in type I fibres at 40% VO2(max.) supports the idea that type I is the fibre type predominantly recruited during low-intensity exercise. The increase of NADH in both fibre types after exercise at 75% and 100% VO2(max.) suggests that the availability of oxygen relative to the demand is decreased in both fibre types at high exercise intensities.

Humans↗