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At least 19 recordsLinked to original sources
PubMed2002

Synthesis rate of muscle proteins, muscle functions, and amino acid kinetics in type 2 diabetes.

Improvement of glycemic status by insulin is associated with profound changes in amino acid metabolism in type 1 diabetes. In contrast, a dissociation of insulin effect on glucose and amino acid metabolism has been reported in type 2 diabetes. Type 2 diabetic patients are reported to have reduced muscle oxidative enzymes and VO(2max). We investigated the effect of 11 days of intensive insulin treatment (T(2)D+) on whole-body amino acid kinetics, muscle protein synthesis rates, and muscle functions in eight type 2 diabetic subjects after withdrawing all treatments for 2 weeks (T(2)D-) and compared the results with those of weight-matched lean control subjects using stable isotopes of the amino acids. Whole-body leucine, phenylalanine and tyrosine fluxes, leucine oxidation, and plasma amino acid levels were similar in all groups, although plasma glucose levels were significantly higher in T(2)D-. Insulin treatment reduced leucine nitrogen flux and transamination rates in subjects with type 2 diabetes. Synthesis rates of muscle mitochondrial, sarcoplasmic, and mixed muscle proteins were not affected by glycemic status or insulin treatment in subjects with type 2 diabetes. Muscle strength was also unaffected by diabetes or glycemic status. In contrast, the diabetic patients showed increased tendency for muscle fatigability. Insulin treatment also failed to stimulate muscle cytochrome C oxidase activity in the diabetic patients, although it modestly elevated citrate synthase. In conclusion, improvement of glycemic status by insulin treatment did not alter whole-body amino acid turnover in type 2 diabetic subjects, but leucine nitrogen flux, transamination rates, and plasma ketoisocaproate level were decreased. Insulin treatments in subjects with type 2 diabetes had no effect on muscle mitochondrial protein synthesis and cytochrome C oxidase, a key enzyme for ATP production.

Amino Acids↗
PubMed1991

Effects of reduced renal function and dietary protein on muscle protein synthesis.

We describe a rat model of renal failure that separates catabolic and anabolic states from each other. Muscle protein synthesis was compared during the anabolic period between sham (S) operated and renal failure (RF) rats that were fed different levels of dietary protein. Male rats weighing between 60 and 80 g first had a partial left nephrectomy and then were given a tryptophan deficient diet from four to six days to induce weight loss. On the second day of the diet either a renal decapsulation (S rats) or a simple right nephrectomy (RF rats) was done to enhance the catabolic response in both and to induce renal failure in the RF rats. Following the period of feeding the deficient diet, both groups were fed a nutritionally complete 14, 17, 20 or 30% protein diet for three to five days. This induced a brisk anabolic response as measured by weight gain. Differences in body weight between the S and RF rats after three to five days on the repletion diet generally was less than 10%. The rats then were fasted overnight, fed a standard meal and muscle protein synthesis (Sm%) was measured two hours post-feeding. Sm% was estimated from the incorporation of 3H phenylalanine (PHE) into muscle 10 minutes following the i.v. injection of 3HPHE (25 muCi/100 g body wt) with carrier PHE to flood all the precursor amino acid pools. Weight loss in the catabolic phase was greater and the net weight gain for the two phases was less in the RF group. Overall, renal failure resulted in a significant reduction in Sm% (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1980

[Preparation of a polyvalent antiserum specific for human muscle proteins. I. Muscle extraction: a macromethod and a micromethod].

Protein metabolism may be upset dramatically by several pathological condition such as starvation, malnutrition, surgical stress. Serum proteins have been investigated in many works but very few studies exist about muscle and organ proteins. This article describes two methods for extraction of muscle water soluble proteins: a macromethod that uses some hundred grams of tissue, and a micromethod that starts from a little muscle biopsia. Extracts have been tested for protein content by electrophoresis on cellulose acetate and isoelectrofocusing on polyacrylamide gel and have shown a rich variety of protein fractions.

Animals↗
PubMed1993

Hindlimb protein turnover and muscle protein synthesis in lambs: a comparison of techniques.

A combination of arterio-venous difference, kinetic isotope transfer and blood flow rate techniques were used to measure tyrosine metabolism across hindlimb tissues of nine growing lambs (average live weight 36.5 kg) fed on a range of dry matter intakes. Muscle protein synthesis was measured using a continuous infusion technique and compared with simultaneous estimates of hindlimb protein turnover calculated from the values for tyrosine metabolism. When the specific radioactivity (SRA) of tyrosine in the arterial plasma free pool was assumed to be the same as the SRA of tyrosine in the direct precursor pool of protein synthesis, hindlimb protein synthesis (ksav; 3.66 (SEM 0.50) %/d) was significantly (P < 0.001) higher (68%) than muscle protein synthesis (ksp; 2.18 (SEM 0.31) %/d) but was similar to the value for muscle protein synthesis calculated using the homogenate free tyrosine SRA (ksh; 3.35 (SEM 0.42) %/d). Hindlimb and muscle protein synthesis (y) were both significantly related to dry matter intake (chi) (ksav, r2 0.667, P = 0.007; ksh, r2 0.968, P < 0.001) and there was no significant difference between the slopes (P = 0.532) and intercepts (P = 0.945) of the two regression lines. The results demonstrate that hindlimb protein turnover cannot be quantitatively compared with muscle protein synthesis, probably due to high protein metabolic activity in non-muscular tissues within the hindlimb, although similar responses in protein synthetic rate to the level of feed intake were observed between hindlimb and muscle tissues.

Animals↗
PubMed2001

Increased concentration of tracee affects estimates of muscle protein synthesis.

Muscle protein synthesis was measured by infusion of L-[2H(5)]phenylalanine in two groups of anesthetized dogs, before and during infusion of insulin with euaminoacidemia, and with differing concentrations of unlabeled phenylalanine (tracee). With the infusion of insulin, muscle protein synthesis increased 39 +/- 12% based on phenylalanyl-tRNA. Calculation with plasma phenylalanine enrichment overestimated insulin stimulation by 40% (56 +/- 12 vs. 39 +/- 12%). Raising the concentration of plasma phenylalanine twofold during infusion of insulin further increased the apparent stimulation of muscle protein synthesis based on plasma relative to phenylalanyl-tRNA by 225% (65 +/- 19 vs. 20 +/- 14%, P < 0.001). In both experiments, the stimulation of synthesis rates calculated from phenylalanine enrichment within the muscle was closer to that from phenylalanyl-tRNA (48 +/- 19%, experiment 1; 30 +/- 14%, experiment 2). Results indicate that the enrichment of a labeled amino acid within plasma and tissue amino acid pools is affected by the concentration of tracee infused. Increasing the concentration of tracee overestimates the insulin-mediated stimulation of muscle protein synthesis when amino acid pools other than aminoacyl-tRNA are used as the precursor enrichment.

Amino Acids↗
PubMed1991

Effects of dietary protein intake on muscle protein synthesis and degradation in rats with gentamicin-induced acute renal failure.

In the study presented here, the muscle protein synthesis and degradation in gentamicin-induced acute renal failure were examined in rats fed a low (7%)-, normal (22%)-, and high (35%)-isocaloric protein diet. Male Sprague-Dawley rats were fed equivalent amounts of these diets for 10 days and then received daily subcutaneous injections of either 1 mL of sterile isotonic saline or 100 mg/kg of gentamicin for 7 consecutive days. The rats were sacrificed the following day, and epitrochlearis muscles were obtained for measurement of protein turnover. The serum creatinine in each of the gentamicin-treated groups were significantly higher than that in the saline-treated controls but were no different from each other. Muscle protein synthesis (calculated from the incorporation of radiolabeled (U-14C) phenylalanine) was slightly but not significantly decreased in gentamicin-treated rats as compared with that of the corresponding saline controls in each of the dietary groups. Net protein degradation (the rate of tyrosine release into media) in the 7 and 22% gentamicin-treated groups was similar to that in the corresponding saline controls. In contrast, net protein degradation was significantly greater in the 35% gentamicin group of rats when compared with that in the 7 and 22% gentamicin groups and its own control. In the 7 and 22% saline- and gentamicin-treated protein groups, there was a reduction in net protein degradation in response to insulin. In contrast, the net protein degradation continued to remain significantly elevated in the 35% gentamicin-treated group, despite addition of insulin, when compared with that in the 7 and 22% gentamicin groups and its own control.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Kidney Injury↗
PubMed2002

Aminoacyl-tRNA enrichment after a flood of labeled phenylalanine: insulin effect on muscle protein synthesis.

Muscle protein synthesis in dogs measured by flooding with L-[(2)H(5)]phenylalanine (70 mg/kg) was significantly stimulated by infusion of insulin with amino acids. The stimulation of muscle protein synthesis was similar when calculated from the enrichment of phenylalanyl-tRNA (61 +/- 10%, P < 0.001), plasma phenylalanine (61 +/- 10%, P < 0.001), or tissue fluid phenylalanine (54 +/- 10%, P < 0.001). The time course for changes in enrichment of L-[(2)H(5)]phenylalanine throughout the flooding period was determined for plasma, tissue fluid, and phenylalanyl-tRNA in the basal state and during the infusion of insulin with amino acids. Enrichments of plasma free phenylalanine and phenylalanyl-tRNA were equalized between 20 and 45 min, although the enrichment of phenylalanyl-tRNA was lower at early time points. Rates of muscle protein synthesis obtained with the flooding method and calculated from plasma phenylalanine enrichment were comparable to those calculated from phenylalanyl-tRNA and also to those obtained previously with a continuous infusion of phenylalanine with phenylalanyl-tRNA as precursor. This study confirms that, with a bolus injection of labeled phenylalanine, the enrichment of aminoacyl-tRNA, the true precursor pool for protein synthesis, can be assessed from more readily sampled plasma phenylalanine.

Amino Acids↗
PubMed1980

Effect of corticosterone and protein malnutrition on muscle protein breakdown in vivo in rats as measured by the urinary excretion of 3-methylhistidine.

The role of corticosterone in regulating the rate of muscle protein breakdown was evaluated by measuring the urinary excretion of 3-methylhistidine (3-Mehis) during the administration of 0.0 (vehicle), 0.8 (physiological dose) and 10 (pharmacological dose) mg of the glucocorticoid/100 g body weight/day to adrenalectomized rats (AdX, AdX 0.8 and AdX 10 respectively). A fourth group of intact rats receiving only vehicle (In) was included as control. Rats were fed on either adequate protein and energy (Co) or low-protein (1-P) diets, for eight consecutive days. No differences were found between AdX and AdX 0.8 groups as compared to the In group in regard to body and liver weights. The AdX 10 group exhibited a significant reduction in body weight and a considerable increase in liver weight; these results were found in rats fed on the Co and 1-P diets, although rats on the 1-P diet showed a proportional decrease in those parameters as compared to the rats fed on the Co diet. Gastrocnemius, tibialis and E.D.L. muscle weights were significantly reduced in AdX 10 group, approximatley at the same extent in the two dietary groups. Soleus muscle weight increased in the AdX 10 group, at the same extent in the two dietary groups, as compared to the In group. Plasma corticosterone levels were significantly greater in the AdX 10 group in both dietary treatments, though restriction of protein in the diet induced a higher plasma hormone level than that of the Co group. Urea-N and creatinine outputs were significantly higher in the AdX 10 group. 3-Mehis excretion underwent an immediate and significant rise in the AdX 10 group, although rats fed on 1-P diet showed a more persistent rise than those fed on the Co diet. No differences were found among the other groups. It is concluded that high plasma corticosterone levels can accelerate muscle protein breakdown and that this action is not seriously affected by the protein content of the diet.

Adrenalectomy↗
PubMed1979

Synthesis of the calcium transport ATPase of sarcoplasmic reticulum and other muscle proteins during development of muscles cells in vivo and in vitro.

The effect of medium Ca2+ concentration upon the concentration and the rate of synthesis of muscle proteins was investigated in chicken pectoralis muscle cultures. There is an easily identifiable class of muscle protein which includes the Ca2+-ATPase of sarcoplasmic reticulum, myosin, troponin C, ATP : creatine phosphotransferase, muscle specific actin, tropomysin 1 and 2, and muscle hemagglutinin, which show a large increase in concentration during normal development. The increased synthesis of these proteins was inhibited, without inhibition of cell proliferation, in culture media of relatively low Ca2+ concentration, 0.05--0.3 mM, where fusion was prevented. Similar medium Ca2+ concentration was required for the expression of all these proteins, suggesting their coordinate regulation. The proteins are denoted as 'calcium-modulated proteins'. The increased Ca2+ transport activity of sarcoplasmic reticulum in cultured chicken pectoralis muscle cells during development at 1.8 mM medium calcium concentration represents de novo synthesis of the Ca2+ transport ATPase, as shown by immunoprecipitation, active site labeling and direct identification of the Ca2+ transport ATPase on two-dimensional gel electropherograms of whole muscle homogenates. The concentration and the turnover rate of the majority of the muscle proteins is not affected significantly by medium Ca2+ concentration between 0.06 and 1.8 mM. It is proposed that increase in cytoplasmic free Ca2+ concentration during fusion plays a central role in the regulation of the synthesis of calcium-modulated proteins.

Acetylcholinesterase↗
PubMed1988

Rates of muscle protein synthesis in paraspinal muscles: lateral disparity in children with idiopathic scoliosis.

1. The rate of paraspinal (multifidus) muscle protein synthesis was measured bilaterally at the top, apex and bottom of the thoracic curve in nine children with an idiopathic scoliosis, using the stable-isotope-labelled amino acid L-[1-13C]leucine. 2. No significant difference was observed in rates of muscle protein synthesis between the two sides of the spine, at the levels of the first vertebrae in neutral alignment at the top and bottom of the curve. However, in every patient, at the apex of the spinal curve, synthesis was higher on the convexity than on the concavity (0.077 +/- 0.04 %/h convex, 0.052 +/- 0.02 %/h concave, mean +/- SD, P less than 0.01). 3. Muscle RNA activity (microgram of protein synthesized h-1 microgram-1 of RNA) was lower at the curve apices on the concave than the convex side (0.019 +/- 0.09 microgram h-1 microgram-1 convex apex, 0.016 +/- 0.06 microgram h-1 microgram-1 concave apex, P less than 0.05). Activities were similar on the two sides at the top and bottom of the curve. 4. Differences in muscle histology between the two sides were also observed only at the apex, with a lower type I fibre diameter (50.9 +/- 8.5 micron convex, 38.3 +/- 2.4 microns concave, P less than 0.05) and a lesser proportion of type I fibres (63 +/- 12% convex, 49 +/- 9% concave, P less than 0.05) on the concavity. 5. The results are consistent with effects on muscle protein turnover secondary to an increased muscle contractile activity on the curve convexity and functional immobilization of the muscle on the curve concavity.

Adolescent↗
PubMed1999

Skeletal muscle injury induced by eccentric muscle action: muscle proteins as markers of muscle fiber injury.

Muscular overuse after high force eccentric muscle action is associated with structural damage of the contractile apparatus that can be observed as Z-line steaming and myofibrillar disruption. Mechanical stress is the major contributing factor for inducing muscle injury, which initiates a cascade of processes resulting in skeletal muscle damage. Disturbances in Ca2+ homeostasis with elevated intracellular [Ca2+] activates the nonlysomal cysteine protease, calpain. Calpain is assumed to play an important role in triggering the response of skeletal muscle protein breakdown, of inflammatory changes, and of regeneration processes in response to eccentric muscle action. The inflammatory response is attributed to changes in hormone and cytokine levels in blood and skeletal muscle. To assess the amount of skeletal muscle damage, plasma CK activity and plasma myoglobin levels have been widely used as markers for muscle injury. As the cytosolic proteins do not necessarily reflect the amount of structural damage, structurally bound proteins such as myosin heavy chains and troponin have been investigated. This paper briefly reviews the cascade of events causing muscle cell injury after unaccustomed eccentric muscle action and the potential of muscle proteins as markers of skeletal muscle damage.

Animals↗
PubMed1984

Effect of a protein-free diet on muscle protein turnover and nitrogen conservation in euthyroid and hyperthyroid rats.

Although protein turnover in skeletal muscle is increased in hyperthyroidism and decreased in hypothyroidism, a deficient protein intake tends to increase serum T3 (tri-iodothyronine) while decreasing muscle protein turnover. To determine whether this diet-induced decrease in protein turnover can occur independent of thyroid status, we have examined muscle protein turnover and nitrogen conservation in hyperthyroid rats fed on a protein-free diet. After inducing hyperthyroidism by giving 20 micrograms of T3/100g body wt. daily for 7 days, groups of euthyroid and hyperthyroid animals were divided into subgroups fed on basal and protein-free diets. Muscle protein turnover was measured by N tau-methylhistidine excretion and [14C]tyrosine infusion. Urinary nitrogen output of euthyroid and hyperthyroid animals fed on the protein-free diet was also measured. Although hyperthyroidism increased the baseline rates of muscle protein synthesis and degradation, it did not prevent a decrease in these values in response to protein depletion. Furthermore, hyperthyroid rats showed greatly decreased nitrogen excretion in response to the protein-free diet, although not to values for euthyroid rats. These findings suggest that protein depletion made the experimental animals less responsive to the protein-catabolic effects of T3.

Animals↗