Measurement of skeletal muscle collagen breakdown by microdialysis

Effects of Collagen Peptides on Recovery Following Eccentric Exercise in Resistance-Trained Males-A Pilot Study

The authors sought to determine whether consuming collagen peptides (CP) enhances musculoskeletal recovery of connective tissues following a damaging exercise bout. Resistance-trained males consumed 15 g/day of CP (n = 7) or placebo (n = 8), and after 7 days, maximal voluntary isometric contraction (MVIC), countermovement jump height, soreness, and collagen turnover were examined. Five sets of 20 drop jumps were performed and outcome measures were collected 24, 48, and 120 hr postexercise. Countermovement jump height was maintained in the CP group at 24 hr (PRE = 39.9 ± 8.8 cm vs. 24 hr = 37.9 ± 8.9 cm, p = .102), whereas the CP group experienced a significant decline at 24 hr (PRE = 40.4 ± 7.9 cm vs. 24 hr = 35.5 ± 6.4 cm, p = .001; d = 0.32). In both groups, muscle soreness was significantly higher than PRE at 24 hr (p = .001) and 48 hr (p = .018) but not at 120 hr (p > .05). MVIC in both legs showed a significant time effect (left: p = .007; right: p = .010) over the 5-day postexercise period. Neither collagen biomarker changed significantly at any time point. CP supplementation attenuated performance decline 24 hr following muscle damage. Acute consumption of CP may provide a performance benefit the day following a bout of damaging exercise in resistance-trained males.

The impact of loading, unloading, ageing and injury on the human tendon

A tendon transfers force from the contracting muscle to the skeletal system to produce movement and is therefore a crucial component of the entire muscle-tendon complex and its function. However, tendon research has for some time focused on mechanical properties without any major appreciation of potential cellular and molecular changes. At the same time, methodological developments have permitted determination of the mechanical properties of human tendons in vivo, which was previously not possible. Here we review the current understanding of how tendons respond to loading, unloading, ageing and injury from cellular, molecular and mechanical points of view. A mechanistic understanding of tendon tissue adaptation will be vital for development of adequate guidelines in physical training and rehabilitation, as well as for optimal injury treatment.

Existence of life-time stable proteins in mature rats-Dating of proteins' age by repeated short-term exposure to labeled amino acids throughout age

In vivo turnover rates of proteins covering the processes of protein synthesis and breakdown rates have been measured in many tissues and protein pools using various techniques. Connective tissue and collagen protein turnover is of specific interest since existing results are rather diverging. The aim of this study is to investigate whether we can verify the presence of protein pools within the same tissue with very distinct turnover rates over the life-span of rats with special focus on connective tissue. Male and female Lewis rats (n = 35) were injected with five different isotopically labeled amino acids tracers. The tracers were injected during fetal development (Day -10 to -2), after birth (Day 5-9), at weaning (Day 25-32) at puberty (Day 54-58) and at adulthood (Day 447-445). Subgroups of rats were euthanized three days after every injection period, at different time point between injection periods and lastly at day 472. Tissue (liver, muscle, eye lens and patellar tendon) and blood samples were collected after euthanization. The enrichment of the labeled amino acids in the tissue or blood samples was measured using GC-MS-MS. In muscle and liver we demonstrated a rapid decrease of tracer enrichments throughout the rat's life, indicating that myofibrillar and cytoskeleton proteins have a high turnover. In contrast, the connective tissue protein in the eye lens and patellar tendon of the mature rat showed detainment of tracer enrichment injected during fetal development and first living days, indicating very slow turnover. The data support the hypothesis that some proteins synthesized during the early development and growth still exist much later in life of animals and hence has a very slow turnover rate.

High insulin combined with essential amino acids stimulates skeletal muscle mitochondrial protein synthesis while decreasing insulin sensitivity in healthy humans

CONTEXT

Insulin and essential amino acids (EAAs) regulate skeletal muscle protein synthesis, yet their independent effects on mitochondrial protein synthesis (MiPS) and oxidative function remain to be clearly defined.

OBJECTIVE

The purpose of this study was to determine the effects of high or low insulin with or without EAAs on MiPS.

DESIGN

Thirty participants were randomized to 3 groups of 10 each with each participant studied twice. Study groups comprised (1) low and high insulin, (2) low insulin with and without EAAs, and (3) high insulin with and without EAAs.

SETTING

The study was conducted in an in-patient clinical research unit.

PARTICIPANTS

Eligible participants were 18 to 45 years old, had a body mass index of <25 kg/m(2), and were free of diseases and medications that might impair mitochondrial function.

INTERVENTION

Low (∼ 6 μU/mL) and high (∼ 40 μU/mL) insulin levels were maintained by iv insulin infusion during a somatostatin clamp while maintaining euglycemia (4.7-5.2 mM) and replacing GH and glucagon. The EAA infusion was 5.4% NephrAmine. l-[ring-(13)C6]Phenylalanine was infused, and muscle needle biopsies were performed.

MAIN OUTCOMES

Muscle MiPS, oxidative enzymes, and plasma amino acid metabolites were measured.

RESULTS

MiPS and oxidative enzyme activities did not differ between low and high insulin (MiPS: 0.07 ± 0.009 vs 0.07 ± 0.006%/h, P = .86) or between EAAs and saline during low insulin (MiPS: 0.05 ± 0.01 vs 0.07 ± 0.01, P = .5). During high insulin, EAAs in comparison with saline increased MiPS (0.1 ± 0.01 vs 0.06 ± 0.01, P < .05) and cytochrome c oxidase activity (P < .05) but not citrate synthase (P = .27). EAA infusion decreased (P < .05) the glucose infusion rates needed to maintain euglycemia during low (∼ 40%) and high insulin (∼ 24%).

CONCLUSION

EAAs increased MiPS and oxidative enzyme activity only with high insulin concentrations.