Changes In Muscle Metabolism Research Articles

Effect of limb immobilization on skeletal muscle.

The immobilization of limbs resulted in atrophy of those muscles that are fixed either at or less than resting length. The loss in protein in these muscles can be described by a first-order equation. Decreases in protein synthesis rate in muscles of immobilized limbs occur during the first 6 h of immobilization, and this decrease probably played a role in initiating muscular atrophy. After weeks of immobilization, muscles composed predominately of slow-twitch fibers took on properties characteristic of fast twitch muscles. The EMG activity of muscles in immobilized limbs was reduced to 5--15% of control levels. Insulin responsiveness for 2-deoxyglucose uptake into the soleus muscle of a limb is decreased at the 24th h of limb immobilization. Muscles of immobilized limbs have either no change or a decrease in resting membrane potential, an increase in extrajunctional acetylcholine receptors of lesser magnitude than the increase that occurred in denervated muscle, and no change in acetylcholinesterase activity in neuromuscular junctions. Immobilizing muscles at stretched lengths prevented the decrease in nerve afterhyperpolarization that was seen in muscles immobilized at shortened positions. These observations suggested that metabolic changes in muscles have a retrograde trophic influence on motor nerves. The model of limb immobilization permits the study of many fundamental problems concerned with mechanisms by which a muscle adapts so that it can meet the requirements of the external environment.

Effects of acute metabolic acidosis on renal, gut, liver, and muscle metabolism of glutamine and ammonia in the dog

Previous studies have shown a rise in arterial glutamine in acute acidosis in the dog. In these experiments glutamine and ammonia metabolism was studied in anesthetized dogs during normal acid-base status and following acute hydrochloric acidosis to determine the mechanism for the rise in arterial glutamine in acidosis. Splanchnic, liver, renal, and hind-half extraction/production were measured by arteriovenous (A-V) sampling and simultaneous blood flow measurements using electromagnetic flow probes. In the normal dog, muscle produced glutamine, and the kidneys, gut, hepatosplanchnic bed, and liver extracted it. Whole blood arterial glutamine rose in acidosis. Renal and muscle glutamine and ammonia extraction/production were unchanged. Gut ammonia release and hepatic ammonia uptake increased by similar amounts in acidosis, but no change in gut glutamine uptake occurred. Hepatic and total hepatosplanchnic glutamine uptake was markedly reduced thereby contributing to the raised arterial glutamine. These results demonstrate that acute metabolic acidosis in the dog-influences marked changes in glutamine extraction and ammonia metabolism across the hepatosplanchnic bed without significant changes in kidney or muscle metabolism.

Ezymatic changes in serum and tissues in fowl infected with a neurotropic‐mesogenic strain of Newcastle disease virus

Chickens aged 6 weeks were inoculated intravenously with two strains of Newcastle disease virus: a mesogenic strain (MAJ) with relatively high neurotropism and a lentogenic strain (V5K7E1). The levels of several enzymes were determined in serum and in various tissues of the infected birds. A marked increase in lactic dehydrogenase (LDH) level in skeletal muscles and a decrease of LDH activity in liver were found in chickens infected with the MAJ strain. Differentiation of LDH isoenzymes by either heating or electrophoresis indicated a significant elevation of LDH 5 iso-enzyme in breast muscle and of LDH 1 in leg muscle, while the activity of LDH 1 in liver decreased. Similar changes were found in the activity of hydroxy butyrate dehydrogenase. Infection with the MAJ strain caused an increase of acid phosphatase activity in breast muscle, a marked decrease of alkaline phosphatase and malate dehydrogenase and an increase of glutamate-oxaloacetate transaminase activities in the intestine. These findings indicate the origin of the changes in enzyme levels found in serum. The possibility of metabolic changes in muscles and liver resulting from damage to the central nervous system is discussed. Inoculation of chickens with the lentogenic strain produced no significant change in the enzyme profile of tissues and serum.

Time course of muscle metabolic changes during tourniquet ischemia in man.

Muscle biopsies form the vastus lateralis muscle of the thigh were obtained from 11 patients before and at 15-min intervals following tourniquet application and 15 min after tourniquet release. The total circulatory occlusion time varied from 60 to 120 min. The concentrations of lactate, creatine phosphate and adenosine triphosphate were determined, and the muscle temperature was recorded. During the ischemic period, the lactate concentration increased from 1.9 mmol x kg-1 wet wt to 14.9 mmol x kg-1 wet wt after 90 min of ischemia. During the last 30 min of ischemia, no further increase in lactate concentration was observed. The creatine phosphate concentration decreased from 20.4 to 5.2 mmol x kg-1 wt wt after 120 min of ischemia. The temperature fell rapidly during the first 15 min from 35.9 degrees to 33.5 degrees and was then constant until 95 min when a further small decrease was observed. The adenosine triphosphate concentration did not change significantly during the ischemic period.

When is it justified to stop the pill?

<h3>Aim</h3> To provide an evidence-based review of muscle metabolism changes with sex-, age- and maturation with reference to the development of youth sport performance. <h3>Methods</h3> A narrative review of data from both invasive and non-invasive studies, from 1970 to 2015, founded on personal databases supported with computer searches of PubMed and Google Scholar. <h3>Results</h3> Youth sport performance is underpinned by sex-, age- and maturation-related changes in muscle metabolism. Investigations of muscle size, structure and metabolism; substrate utilisation; pulmonary oxygen uptake kinetics; muscle phosphocreatine kinetics; peak anaerobic and aerobic performance; and fatigue resistance; determined using a range of conventional and emerging techniques present a consistent picture. Age-related changes have been consistently documented but specific and independent maturation-related effects on muscle metabolism during exercise have proved elusive to establish. Children are better equipped for exercise supported primarily by oxidative metabolism than by anaerobic metabolism. Sexual dimorphism is apparent in several physiological variables underpinning youth sport performance. As young people mature there is a progressive but asynchronous transition into an adult metabolic profile. <h3>Conclusions</h3> The application of recent developments in technology to the laboratory study of the exercising child and adolescent has both supplemented existing knowledge and provided novel insights into developmental exercise physiology. A sound foundation of laboratory-based knowledge has been established but the lack of rigorously designed child-specific and sport-specific testing environments has clouded the interpretation of the data in real life situations. The primary challenge remains the translation of laboratory research into the optimisation of youth sports participation and performance.

Metabolic changes in muscle on long-term alprenolol therapy.

Muscle biopsies from the vastus muscle were taken at rest and immediately after upright bicycle exercise at 50% of the individual VO2max, before and during 6 wk of alprenolol treatment (200 to 400 mg twice daily) in 6 untrained patients with essential hypertension. Resting muscle concentrations (mmole - kg-1 - wet weight) of glycogen, glucose, lactate, and high-energy phosphates [adenosine triphosphate (ATP) and creatine phosphate (CP)] were not affected by alprenolol treatment, but after 10 min after exercise the glycogenolysis increased and depletion of ATP and CP was enhanced. The relationship between blood and muscle lactate was altered by alprenolol, indicating that alprenolol prevents lactate translocation from the muscle to the blood. The results show that during moderate exercise, leg muscle metabolism is influenced by long-term antihypertensive therapy.

Amino aciduria in weightlessness

Urinary excretion of amino acids by the 9 Skylab crewmen was studied as an indicator of the metabolic effects caused by exposure to the space flight environment. Intake was consistent in quality and quantity throughout the 28, 59 and 84-day flights for each of the crewmen and complete collections were accomplished. The results indicated an increased excretion in most amino acids during the first month of flight which remained elevated in the second and third months but to a lesser extent. Additional indications of change in muscle and skeletal metabolism were observed. These results point to the desirability of obtaining additional indices of alterations in protein synthetic processes in conjunction with future space flights.

Biochemical alterations in denervated skeletal muscle and transected sciatic nerve in the hibernating ground squirrel

Biochemical intermediates associated with energy metabolism were measured in innervated and denervated anterior tibialis muscles of nonhibernating ground squirrels to gain insight into mechanisms associated with changes that occur during hibernation and subsequent to denervation. Steady-state concentrations of glucose, glucose 6-phosphate, and lactate in the innervated muscles were decreased 42, 75, and 78%, respectively, during hibernation. Upon awakening, the concentration of glucose was increased approximately two-fold and that of lactate was elevated about 10-fold and glucose-6-phosphate more than 15-fold. These findings were interpreted as indicating that glycolysis was reduced during hibernation and elevated suddenly and markedly immediately after hibernation. A similar effect was noted in denervated muscles of hibernating animals. The reduction in concentrations of glycolytic intermediates of innervated and denervated muscles during hibernation was accompanied by a decrease in the total reserves of high-energy phosphate; however, ATP : ADP ratios were not changed significantly. Denervation produced significant decreases in concentrations of glucose 6-phosphate and significant increases in glutamate in muscles of hibernating and nonhibernating animals. Decreases in glucose 6-phosphate were accompanied by significant decreases in fructose 1,6-diphosphate in denervated muscles of hibernating animals. Subsequent to denervation, phosphocreatine increased by 55% in muscles from hibernating animals but did not change in muscles from nonhibernating animals. The changes in phosphocreatine in denervated muscles from hibernating animals are accompanied by an increase in the total energy reserves of these muscles. Metabolic changes in muscles from hibernating animals appear to occur in the absence of any degeneration of transected sciatic nerves. High energy phosphate as well as choline acetylase and acetylcholinesterase are maintained at normal activities in nerves from hibernating squirrels for at least 3 weeks subsequent to separation of axons from nerve cell bodies.

Skeletal muscle metabolism and ultrastructure in relation to age in sedentary men.

In order to find out if there are age-related changes in human skeletal muscle metabolism or ultrastructure, biopsy material from 56 sedentary men aged 22-65 years was studied by means of enzyme activity determinations, histochemistry and quantitative electron microscopy. For comparison, a younger (16-18 years) and an older (66-76 years) group were included. These subjects were relatively more active. There was an increase in percentage of slow twitch fibres with age. Mitochondrial volume fraction decreased with age, primarily due to diminished mean mitochondrial volume. In spite of this, no overall decrease in the activities of five enzymes, representative of the major pathways in energy metabolism, was observed. Thus, increased amounts of enzymes per unit mitochondrial volume are implicated. Lipofuscin was more frequently found in the older groups. Correlations were present between fibre type distribution and oxidative enzymes, as well as between different enzymes. It was concluded, that the decrease in maximal oxygen uptake and muscular strength in aging humans probably may not be explained in terms of a deteriorating skeletal muscle energy metabolism.

Morphological and Metabolic Changes in Muscles of Hibernating Lizards

and Leiolopisma zelandica) was investigated histochemically and electron microscopically in the active and hibernating states. Hibernation resulted in a reduction of muscle fiber diameters, a close packing of myofibrils and enlargement of T tubules and sarcoplasmic reticulum. Skeletal muscle glycolytic enzymatic activity was uniformly reduced in hibernation but muscle glycogen stores were preserved. Oxidative enzymatic activity was less uniformly reduced in the skeletal muscles of hibernating geckos and skinks. Winter lizards had greater muscle esterase activity without evidence of increased ketone formation. It is concluded that the energy requirements of skeletal muscle in hibernating lizards are largely met by an increased degradation of fatty acids.

Changes in liver and skeletal muscle metabolism during parenteral feeding

The content of nucleic acids and of readily extracted protein in the liver and skeletal muscle was investigated in rats with alloxan diabetes fed parenterally with various protein digests. Administration of these sources of nitrogen was shown to activate nucleic acid metabolism and thus to promote the restoration of protein metabolism.

Action of diazoxide on skeletal muscle vascular resistance.

Controversy exists as to whether arteriolar dilation after diazoxide (DZ) administration is due to a prolonged vascular effect that outlasts the presence of circulating levels of DZ or to equilibrium of arteriolar sites with circulating DZ. To resolve this question, the direct effects of DZ on the vascular resistance (VR) of the isolated blood-perfused (constant-flow) gracilis muscle were evaluated in 44 anesthetized dogs. Intra-arterial infusions of DZ resulted in falls in vascular resistance (-35.9±5.5 SEM %) which returned to control levels after the infusions, thus indicating that irreversible binding to arterioles or a prolonged arteriolar effect independent of plasma levels of the drug did not obtain. Decreases (- 16% to -35%) in VR could also be achieved by premixing DZ in the blood perfusion reservoir at concentrations between 40 and 100 mg/L (which may be achieved clinically); thus albumin binding does not abolish the activity of DZ. Decreases in VR by DZ were not related to stimulation of beta-adrenergic receptors, alteration in Na + or K + balance, or changes in venous levels of glucose, lactate, pO 2 , pCO 2 , or pH. When norepinephrine and angiotensin II were infused during diazoxide infusions their vasoconstrictor response was attenuated. Thus DZ has a direct effect in lowering VR which is independent of measurable changes in gracilis muscle metabolism. Moreover, the VR effect of DZ is not dependent on a prolonged arteriolar effect independent of plasma concentrations of the drug.

Production of muscular weakness in rats by a creatine analogue.

IN an effort to clarify the role of abnormal creatine metabolism in producing muscular dystrophy a search for an antimetabolite to creatine has been made. If a specific defect in either the synthesis or utilization of creatine could be produced by an antimetabolite, it would then be possible to assess the change in muscle structure and metabolism which results from impaired creatine metabolism.