Protein ingestion increases myofibrillar protein synthesis after concurrent exercise.

PURPOSE: We determined the effect of protein supplementation on anabolic signaling and rates of myofibrillar and mitochondrial protein synthesis after a single bout of concurrent training. METHODS: Using a randomized crossover design, eight healthy males were assigned to experimental trials consisting of resistance exercise (8 × 5 leg extension, 80% 1RM) followed by cycling (30 min at approximately 70% V˙O2peak) with either postexercise protein (PRO, 25-g whey protein) or placebo (PLA) ingestion. Muscle biopsies were obtained at rest and at 1 and 4 h after exercise. RESULTS: Akt and mTOR phosphorylation increased 1 h after exercise with PRO (175%-400%, P < 0.01) and was different from PLA (150%-300%, P < 0.001). Muscle RING finger 1 and atrogin-1 messenger RNA (mRNA) were elevated after exercise but were higher with PLA compared with those in PRO at 1 h (50%-315%, P < 0.05), whereas peroxisome proliferator-activated receptor gamma coactivator 1-alpha mRNA increased 4 h after exercise (620%-730%, P < 0.001), with no difference between treatments. Postexercise rates of myofibrillar protein synthesis increased above rest in both trials (75%-145%, P < 0.05) but were higher with PRO (67%, P < 0.05), whereas mitochondrial protein synthesis did not change from baseline. CONCLUSIONS: Our results show that a concurrent training session promotes anabolic adaptive responses and increases metabolic/oxidative mRNA expression in the skeletal muscle. PRO ingestion after combined resistance and endurance exercise enhances myofibrillar protein synthesis and attenuates markers of muscle catabolism and thus is likely an important nutritional strategy to enhance adaptation responses with concurrent training.

Dose-dependent responses of myofibrillar protein synthesis with beef ingestion are enhanced with resistance exercise in middle-aged men.

Aging impairs the sensitivity of skeletal muscle to anabolic stimuli, such as amino acids and resistance exercise. Beef is a nutrient-rich source of dietary protein capable of stimulating muscle protein synthesis (MPS) rates in older men at rest. To date, the dose-response of myofibrillar protein synthesis to graded ingestion of protein-rich foods, such as beef, has not been determined. We aimed to determine the dose-response of MPS with and without resistance exercise to graded doses of beef ingestion. Thirty-five middle-aged men (59 ± 2 years) ingested 0 g, 57 g (2 oz; 12 g protein), 113 g (4 oz; 24 g protein), or 170 g (6 oz; 36 g protein) of (15% fat) ground beef (n = 7 per group). Subjects performed a bout of unilateral resistance exercise to allow measurement of the fed state and the fed plus resistance exercise state within each dose. A primed constant infusion of l-[1-(13)C]leucine was initiated to measure leucine oxidation and of l-[ring-(13)C(6)]phenylalanine was initiated to measure myofibrillar MPS. Myofibrillar MPS was increased with ingestion of 170 g of beef to a greater extent than all other doses at rest and after resistance exercise. There was more leucine oxidation with ingestion of 113 g of beef than with 0 g and 57 g, and it increased further after ingestion of 170 g of beef (all p < 0.05). Ingestion of 170 g of beef protein is required to stimulate a rise in myofibrillar MPS over and above that seen with lower doses. An isolated bout of resistance exercise was potent in stimulating myofibrillar MPS, and acted additively with feeding.

Validation of a single biopsy approach and bolus protein feeding to determine myofibrillar protein synthesis in stable isotope tracer studies in humans.

BACKGROUND: Minimizing the number of muscle biopsies has important methodological implications and minimizes subject discomfort during a stable isotope amino acid infusion. We aimed to determine the reliability of obtaining a single muscle biopsy for the calculation of muscle protein fractional synthetic rate (FSR) as well as the amount of incorporation time necessary to obtain that biopsy after initiating a stable isotope infusion (Study 1). The calculation of muscle protein FSR requires tracer steady-state during the stable isotope infusion. Therefore, a second aim was to examine if steady-state conditions are compromised in the precursor pools (plasma free or muscle intracellular [IC]) after ingestion of a tracer enriched protein drink and after resistance exercise (Study 2). METHODS: Sixteen men (23 ± 3 years; BMI = 23.8 ± 2.2 kg/m2, means ± SD) were randomized to perform Study 1 or Study 2 (n = 8, per study). Subjects received a primed, constant infusion of L-[ring-13C6]phenylalanine coupled with muscle biopsies of the vastus lateralis to measure rates of myofibrillar protein synthesis (MPS). Subjects in Study 2 were fed 25 g of whey protein immediately after an acute bout of unilateral resistance exercise. RESULTS: There was no difference (P = 0.3) in rates of MPS determined using the steady-state precursor-product equation and determination of tracer incorporation between sequential biopsies 150 min apart or using plasma protein as the baseline enrichment, provided the infusion length was sufficient (230 ± 0.3 min). We also found that adding a modest amount of tracer (4% enriched), calculated based on the measured phenylalanine content of the protein (3.5%) in the drink, did not compromise steady-state conditions (slope of the enrichment curve not different from zero) in the plasma free or, more importantly, the IC pool (both P > 0.05). CONCLUSIONS: These data demonstrate that the single biopsy approach yields comparable rates of muscle protein synthesis, provided a longer incorporation time is utilized, to that seen with a traditional two biopsy approach. In addition, we demonstrate that enriching protein-containing drinks with tracer does not disturb isotopic steady-state and thus both are reliable techniques to determine rates of MPS in humans.

Nutrient provision increases signalling and protein synthesis in human skeletal muscle after repeated sprints.

The effect of nutrient availability on the acute molecular responses following repeated sprint exercise is unknown. The aim of this study was to determine skeletal muscle cellular and protein synthetic responses following repeated sprint exercise with nutrient provision. Eight healthy young male subjects undertook two sprint cycling sessions (10 × 6 s, 0.75 N m torque kg(-1), 54 s recovery) with either pre-exercise nutrient (24 g whey, 4.8 g leucine, 50 g maltodextrin) or non-caloric placebo ingestion. Muscle biopsies were taken from vastus lateralis at rest, and after 15 and 240 min post-exercise recovery to determine muscle cell signalling responses and protein synthesis by primed constant infusion of L: -[ring-(13)C(6)] phenylalanine. Peak and mean power outputs were similar between nutrient and placebo trials. Post-exercise myofibrillar protein synthetic rate was greater with nutrient ingestion compared with placebo (~48%, P < 0.05) but the rate of mitochondrial protein synthesis was similar between treatments. The increased myofibrillar protein synthesis following sprints with nutrient ingestion was associated with coordinated increases in Akt-mTOR-S6K-rpS6 phosphorylation 15 min post-exercise (~200-600%, P < 0.05), while there was no effect on these signalling molecules when exercise was undertaken in the fasted state. For the first time we report a beneficial effect of nutrient provision on anabolic signalling and muscle myofibrillar protein synthesis following repeated sprint exercise. Ingestion of protein/carbohydrate in close proximity to high-intensity sprint exercise provides an environment that increases cell signalling and protein synthesis.

Differential stimulation of myofibrillar and sarcoplasmic protein synthesis with protein ingestion at rest and after resistance exercise.

We aimed to determine whether there is a differential stimulation of the contractile myofibrillar and the cellular sarcoplasmic proteins after ingestion of protein and how this is affected by resistance exercise. Fasted (FAST) muscle protein synthesis was measured in seven healthy young men with a primed constant infusion of L-[ring-(13)C(6)]phenylalanine. Participants then performed an intense bout of unilateral resistance exercise followed by the consumption of 25 g of whey protein to maximally stimulate protein synthesis. In the rested (FED) leg myofibrillar (MYO) protein synthesis was elevated (P < 0.01) above FAST at 3 h (approximately 163%) but not at 1 and 5 h (P > 0.05). In contrast, MYO protein synthesis in the exercised (FED-EX) leg was stimulated above FAST at 1, 3 and 5 h (approximately 100, 216, and 229%, respectively; P < 0.01) with the increase at 5 h being greater than FED (P < 0.01). Thus, the synthesis of muscle contractile proteins is stimulated by both feeding and resistance exercise early (1 h) but has a greater duration and amplitude after resistance exercise. Sarcoplasmic (SARC) protein synthesis was similarly elevated (P < 0.01) above FAST by approximately 104% at 3 h in both FED and FED-EX suggesting SARC protein synthesis is stimulated by feeding but that this response is not augmented by resistance exercise. In conclusion, myofibrillar and sarcoplasmic protein synthesis are similarly, but transiently, stimulated with protein feeding. In contrast, resistance exercise rapidly stimulates and sustains the synthesis of only the myofibrillar protein fraction after protein ingestion. These data highlight the importance of measuring the synthetic response of specific muscle protein fractions when examining the effects of exercise and nutrition.

Different profiles of T-cell IFN-gamma and IL-12 in allergen-induced early and dual responders with asthma.

BACKGROUND: IFN-gamma and IL-12 are anti-inflammatory cytokines released from various cells, including T cells. Allergen inhalation by atopic subjects with asthma results in 2 bronchoconstrictor phenotypes, termed isolated early and dual responders . Persistence of allergen-induced airway response and inflammation is a distinctive feature of dual responders. OBJECTIVE: To evaluate the roles of IFN-gamma and IL-12 in resolving allergen-induced airway inflammation by comparing T lymphocytes (CD4 + and CD8 + cells) producing these cytokines in isolated early and dual responders. METHODS: Twenty-four subjects with asthma (12 isolated early and 12 dual responders) were challenged with inhaled allergen. Peripheral blood and induced sputum were taken before and 1 day, 3 days, and 7 days after challenge. Frequency of IFN-gamma, IL-12, IL-4, and IL-13 producing CD4 + and CD8 + cells was assessed by using flow cytometry. RESULTS: After allergen, both CD4 + and CD8 + IFN-gamma positive cells in peripheral blood significantly decreased in dual responders only, whereas CD4 + and CD8 + IFN-gamma positive cells in induced sputum significantly increased in isolated early responders only. By contrast, IL-12 positive cells in peripheral blood significantly increased after allergen challenge only in isolated early responders. The ratio of CD4 + and CD8 + IL-4/IFN-gamma positive cells in peripheral blood significantly decreased in isolated early responders by 3 days and had recovered by 7 days. CONCLUSION: These results suggest that contrasting profiles of IFN-gamma and IL-12 production may be responsible for different time courses of allergen-induced airway responses between isolated early and dual responders.

Effects of montelukast and budesonide on airway responses and airway inflammation in asthma.

Inhaled corticosteroids are effective antiinflammatory therapy for asthma; however, they do not completely abolish allergen-induced airway inflammation. Leukotriene modifiers attenuate both early and late allergen responses and have antiinflammatory properties. We reasoned that treatment with budesonide and montelukast in combination might provide greater antiinflammatory effects than either drug alone, and the purpose of this study was to compare the effects of treatment with budesonide and montelukast, alone or in combination, on outcome variables after allergen inhalation. Ten subjects with asthma with dual responses after allergen inhalation were included in this randomized, double-blind, crossover study. Outcomes included early and late asthmatic responses, and changes in airway responsiveness and sputum eosinophilia, measured before and after challenge. Treatment with montelukast attenuated the maximal early asthmatic response compared with placebo (p < 0.001) and budesonide (p = 0.002). Both budesonide and montelukast, alone and in combination, attenuated the maximal late asthmatic response compared with placebo (p < 0.01). Budesonide and montelukast, alone and in combination, afforded protection against allergen-induced airway hyperresponsiveness (p < 0.05), although the treatment effect of budesonide was greater than that of montelukast (p < 0.05). Treatment with budesonide and montelukast, alone and in combination, also attenuated allergen-induced sputum eosinophilia. Thus, montelukast and budesonide attenuated allergen-induced asthmatic responses, airway hyperresponsiveness, and sputum eosinophilia, although combination treatment did not provide greater antiinflammatory effects than either drug alone.

IL-10 production in circulating T cells differs between allergen-induced isolated early and dual asthmatic responders.

BACKGROUND: IL-10 is an anti-inflammatory cytokine released from various cells, including T cells. The role of IL-10 in asthma pathogenesis remains uncertain. Allergen inhalation by atopic asthmatic subjects results in 2 bronchoconstrictor phenotypes: isolated early response and dual response. Persistence of allergen-induced airway inflammation is a feature of dual responders. OBJECTIVES: The kinetics of IL-10 production in circulating T cells were investigated to examine a potential role of IL-10 in allergen-induced responses and airway inflammation. METHODS: Fourteen subjects with mild asthma (7 isolated early and 7 dual responders) were challenged with allergen. PBMCs taken before and 24 hours after allergen challenge were processed for intracellular IL-10 staining with fluorescent-conjugated anti-IL-10 antibody. The frequency of IL-10-producing cells was assessed for CD4(+) and CD8(+) T-cell subsets by using flow cytometry. RESULTS: Before allergen administration, the frequency of IL-10-producing CD4(+) cells was significantly higher in dual than in isolated early responders. IL-10-producing CD4(+) cells significantly increased after allergen in early responders, whereas IL-10-producing CD4(+) cells significantly decreased in dual responders. Simultaneous assessments of IL-5-producing T cells did not show any differences between each group before or after allergen administration. CONCLUSIONS: These results suggest that the contrasting profiles of IL-10 production may be associated with the different time course of allergen-induced airway inflammation between allergen-induced early and dual responders.