Effect of exercise on adenosine deaminase activity in rat skeletal muscles.

Adenosine deaminase activity was shown to decrease in each skeletal muscle type (the slow-twitch oxydative, fast-twitch oxydative--glycolytic and fast-twitch glycolytic) at the beginning of exercise of moderate intensity and to return to the control when exercise was continued till exhaustion. 5 min occlusion of the femoral artery had no effect on the enzyme activity in either muscle. The reduction of the enzyme activity at the onset of exercise could result in reduction of adenosine breakdown and thus contribute to vasodilation at this stage of increased contractile activity of the muscles.     

Dehydrogenase activity in skeletal muscles of rats after long-term exposure to weightlessness

Malate- and isocytratedehydrogenase activity in mitochondrial and cytoplasmic fractions and lactate dehydrogenase activity in hindlimb muscles have been studied at different stages after 18.5-day flight on a biosatellite "Cosmos-1129" and after 20-day hypokinesia. A decrease in dehydrogenase activity has been found on the first postflight day. The enzyme activities returned to the control values in mitochondria, and in the cytoplasm they were greater by day 6 postflight. It was concluded that hypokinesia did not reveal all the effects of microgravity on the whole system but some enzyme alterations in the muscle resembled those observed during the flight. The effects may be caused by the inhibition of both aerobic and anaerobic metabolic pathways under the effect of microgravity.     

Enhanced matrix metalloproteinase activity in skeletal muscles of rats with congestive heart failure

Patients with congestive heart failure (CHF) are prone to increased skeletal muscle fatigue. Elevated circulatory concentrations of tumor necrosis factor (TNF)-alpha and monocyte chemoattractant protein-1, which may stimulate matrix metalloproteinase (MMP) activity and, thereby, contribute to skeletal muscle dysfunction, are frequently found in CHF. However, whether skeletal muscle MMP activity is altered in CHF is unknown. Hence, we have used a gelatinase assay to assess the activity of MMP and tissue inhibitors of MMP in single skeletal muscles of rats with CHF 6 wk after induction of myocardial infarction. Sham-operated (Sham) rats were used as controls. We also measured the gene expression and protein contents of MMP-2 and MMP-9 in skeletal muscles of these rats. Plasma MMP activity was nearly seven times higher (P < 0.05) in CHF than in Sham rats. Concomitantly, the MMP activity within single slow- and fast-twitch skeletal muscles of CHF rats increased two- to fourfold compared with Sham animals, whereas tissue inhibitor of MMP activity did not differ (P > 0.05). Preformed MMP-2 and MMP-9 were probably activated in CHF, because neither their gene expression nor protein levels were altered (P > 0.05). Serum concentrations of TNF-alpha and monocyte chemoattractant protein-1 remained unchanged (P > 0.05) between CHF and Sham rats during the 6-wk observation period. We conclude that development of CHF in rats enhances MMP activity, which in turn may distort the normal contractile function of skeletal muscle, thereby contributing to increased skeletal muscle fatigue.     

Effect of thyrotoxicosis on the activity of proprioceptors of the skeletal muscles]

A study was made of the influence of prolonged administration of the thyroid hormones on the pulse activity of the cat soleus muscle spindles. In the animals with thyrotoxicosis the response of the primary endings of the spindles on the continuously acting and sudden rapid extension proved to be considerably enhanced both during the dynamic and the static phase. The frequency of discharges of the secondary endings showed no significant changes. It is supported that the changes in the activity of the primary endings observed were connected with the disturbances in the metabolism of the muscle and also with its atrophy.     

Voltage-current relationships in skeletal muscles of rats.

(1) Thin sheets of fibres from gastrocnemius and lumbricalis muscles of rats were washed in Tris-proponiate solutions containing 0.67 to 60 mM K. The voltage-current relationship was measured by the two microelectrode technique. (2) The V-C curve was S-shaped. The steep region, sometimes including a "forbidden" voltage zone, occurred between about -40 and -70 mV when the solution contained 2 mM K. In some fibres the steep region was found to occur at more positive currents and voltages in "upward" runs (steps of increasing depolarizing currents) then in "downward" runs. The V-C curves thus revealed hysteresis loops presumably covering a negative conductance region. (3) The voltage at which the steep region occurred was a function of [K]0. The mid-point of the steep region was 50 to 60 mV more positive than EK for a particular [K]0 was about 6 mM the steep region of the V-C relationship was not conspicuous. The steep V-C region is considered to reflect depolarizing K inactivation. The near disappearance of the phenomenon at 6 mM K is thought to result from an interference of delayed rectification and depolarizing K inactivation.     

The detection of neutrophilic myeloperoxidase in the skeletal muscles of rats after muscle activity

Rat muscle infiltration by neutrophils after muscle activity (MA) was investigated on myeloperoxidase (MPO) concentration. MPO distribution in muscle subcellular fractions was also studied. Increase of MPO concentration in skeletal muscles was discovered after MA. Its maximum was determined within 1-5 days of the rest. This fact can be considered as an evidence of neutrophil influx in muscle tissue. The electroral MPO concentration increase in plasmalemma membrane fraction after MA was shown. In vitro MPO was able to catalyze 125I inclusion in membrane material. These results give a possibility to propose that neutrophil MPO can have a certain significance in muscle tissue damage by haloid joining to plasmalemma proteins.     

Glyconeogenic pathway in isolated skeletal muscles of rats

Although the conversion of lactate to glycogen (glyconeogenesis) in muscle was demonstrated a long time ago, the biochemical reactions responsible for this process are still a controversial matter. In the present study, advantage was taken from the specific inhibition induced by phenylalanine on muscle pyruvate kinase (PK) to investigate the role of reverse PK activity in muscle glyconeogenesis. Addition of phenylalanine to the incubation medium of a preparation of isolated, intact skeletal muscles that maintain metabolic activity for several hours reduced by 50% the rate of incorporation of [14C]lactate or [14C]bicarbonate into muscle glycogen. Muscle extracts presented high levels of maximal activity of PK in the reverse direction, which was completely blocked in the presence of phenylalanine. In contrast, mercaptopicolinic acid, an inhibitor of phosphoenolpyruvate carboxykinase (PEPCK), did not affect the incorporation of 14C from either lactate or bicarbonate into muscle glycogen. Maximal PEPCK activity was much lower in muscle extracts than in gluconeogenic or glyceroneogenic tissues and was suppressed in the presence of mercaptopicolinic acid. The data suggest that a reversal of the metabolic flux through the reaction catalyzed by PK contributes to the accumulation of lactate-derived glycogen that occurs in skeletal muscle under certain physiological conditions.     

Effect of thyroxine on skeletal muscles in hereditary myodystrophia

The influence of 3-week L-thyroxin administration on contractility and histochemical composition of skeletal muscles was studied in 129Rj mice of normal and dystrophic genotypes. The rise in speed characteristics of isometric contraction and percentage of type II "fast" fibers was established in both types of animals. Contractile properties in dystrophic animals, receiving L-thyroxin, showed a tendency towards normalization and were comparable to those of normal animals.     

Effect of trivalent iron on denervated skeletal muscles

The activity of succinic dehydrogenase, myosin ATPase, as well as lactic dehydrogenase (LDG) spectrum and cross-section area of different type of muscle fibers have been studied for 3 weeks after denervation (control) and after denervation and intraperitoneal injection of 10(-6) M FeCl3. Intraperitoneal injection of FeCl3 prevented the development of denervation phenomena (increase in cross-section area of muscle fibers, changes in LDG spectrum).     

Effect of exercise on muscle fibre composition and enzyme activities of skeletal muscles in young rats

Young Wistar rats underwent dynamic (D) or static (S) exercise from the 5th to 35th day after birth. Histochemical and biochemical analysis were performed in the extensor digitorum longus (EDL) and the soleus muscle (SOL). Lactate dehydrogenase (LDH) (regulating anaerobic metabolism) and citrate synthase (CS) and hydroxyacyl-CoA dehydrogenase (HAD) (both regulating aerobic metabolism) activities were determined spectrophotometrically. An increase of the fast oxidative-glycolytic (FOG) muscle fibres was found in the slow SOL muscle in both trained groups, i.e. by 10% in group D and by 7% in group S in comparison with the C group. The EDL muscle fibre distribution did not differ from those of control animals in respect to the slow oxidative (SO) fibre type. A higher percentage of FOG fibres by 19% was found in group D contrary to a decreased number of the fast glycolytic (FG) muscle fibres in this trained group. The greatest increase of CS (EDL 185%, SOL 176%) and HAD (EDL 83%, SOL 178%) activities were found in group D as compared with control group (C). Only small differences were observed in LDH activity. The values of characteristic enzyme activity ratios show that dynamic training resulted in an elevation of oxidative capacity of skeletal muscle, while the static load led preferentially along the glycolytic pathway. It may be concluded that an adaptive response to the training load during early postnatal development is different due to the type of exercise (dynamic or static) and/or the type of skeletal muscle (fast or slow).     

Leucine promotes glucose uptake in skeletal muscles of rats

Soleus muscles isolated from normal rats were incubated to evaluate whether or not leucine promotes glucose uptake under insulin-free conditions, using a labeled 2-deoxyglucose uptake assay. Glucose uptake was promoted by 2mM leucine. A metabolite of leucine, alpha-ketoisocaproic acid (alpha-KIC), also exhibited a similar stimulatory effect, although this was not as potent as leucine. Stimulation of glucose uptake by leucine was completely canceled by pre-treatment with either 10 microM LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3-kinase), or 6 microM GF109203X, a specific inhibitor of protein kinase C (PKC). No significant change was observed by pre-treatment with 1 microM rapamycin, a specific inhibitor of mammalian target of rapamycin (mTOR). These results suggest that leucine stimulates glucose transport in skeletal muscle via PI3-kinase and PKC pathways independently of the mammalian target of mTOR. They also suggest that leucine stimulates glucose transport by an insulin-independent mechanism.     

Activity of thiamine in skeletal muscles od rats]

Thiamine participates in neuromuscular transmission. This transmission is depressed when thiamine level in organism decreases and it is normalized in animals after thiamine injection.