Soy-dairy protein blend and whey protein ingestion after resistance exercise increases amino acid transport and transporter expression in human skeletal muscle.

Increasing amino acid availability (via infusion or ingestion) at rest or postexercise enhances amino acid transport into human skeletal muscle. It is unknown whether alterations in amino acid availability, from ingesting different dietary proteins, can enhance amino acid transport rates and amino acid transporter (AAT) mRNA expression. We hypothesized that the prolonged hyperaminoacidemia from ingesting a blend of proteins with different digestion rates postexercise would enhance amino acid transport into muscle and AAT expression compared with the ingestion of a rapidly digested protein. In a double-blind, randomized clinical trial, we studied 16 young adults at rest and after acute resistance exercise coupled with postexercise (1 h) ingestion of either a (soy-dairy) protein blend or whey protein. Phenylalanine net balance and transport rate into skeletal muscle were measured using stable isotopic methods in combination with femoral arteriovenous blood sampling and muscle biopsies obtained at rest and 3 and 5 h postexercise. Phenylalanine transport into muscle and mRNA expression of select AATs [system L amino acid transporter 1/solute-linked carrier (SLC) 7A5, CD98/SLC3A2, system A amino acid transporter 2/SLC38A2, proton-assisted amino acid transporter 1/SLC36A1, cationic amino acid transporter 1/SLC7A1] increased to a similar extent in both groups (P < 0.05). However, the ingestion of the protein blend resulted in a prolonged and positive net phenylalanine balance during postexercise recovery compared with whey protein (P < 0.05). Postexercise myofibrillar protein synthesis increased similarly between groups. We conclude that, while both protein sources enhanced postexercise AAT expression, transport into muscle, and myofibrillar protein synthesis, postexercise ingestion of a protein blend results in a slightly prolonged net amino acid balance across the leg compared with whey protein.

Endothelial function and the regulation of muscle protein anabolism in older adults.

Sarcopenia, the loss of skeletal muscle mass and function with aging, is a major contributor to frailty and morbidity in older adults. Recent evidence has emerged suggesting that endothelial dysfunction and insulin resistance of muscle protein metabolism may significantly contribute to the development of sarcopenia. In this article we review: 1) recent studies and theories on the regulation of skeletal muscle protein balance in older adults; 2) the link between insulin resistance of muscle protein synthesis and endothelial dysfunction in aging; 3) mechanisms for impaired endothelial responsiveness in aging; and 4) potential treatments that may restore the endothelial responsiveness and muscle protein anabolic sensitivity in older adults.

Supraphysiological hyperinsulinaemia is necessary to stimulate skeletal muscle protein anabolism in older adults: evidence of a true age-related insulin resistance of muscle protein metabolism.

AIMS/HYPOTHESIS: The physiological increase in muscle protein anabolism induced by insulin is blunted in healthy, glucose-tolerant older adults. We hypothesised that the age-related defect in muscle protein anabolism is a true insulin resistance state and can be overridden by supraphysiological hyperinsulinaemia. METHODS: We used dye dilution, stable isotopic and immunoblotting techniques to measure leg blood flow, muscle protein synthesis, protein kinase B/mammalian target of rapamycin (Akt/mTOR) signalling, and amino acid kinetics in 14 healthy, glucose-tolerant older volunteers at baseline, and during an insulin infusion at postprandial (PD, 0.15 mU min(-1) 100 ml(-1)) or supraphysiologically high (HD, 0.30 mU min(-1) 100 ml(-1)) doses. RESULTS: Leg blood flow, muscle protein synthesis, and Akt/mTOR signalling were not different at baseline. During hyperinsulinaemia, leg blood flow (p < 0.01) and muscle protein synthesis increased in the HD group only (PD [%/h]: from 0.063 +/- 0.006 to 0.060 +/- 0.005; HD [%/h]: from 0.061 +/- 0.007 to 0.098 +/- 0.007; p < 0.01). Muscle Akt phosphorylation increased in both groups, but the increase tended to be greater in the HD group (p = 0.07). The level of p70 ribosomal S6 kinase 1 (S6K1) phosphorylation increased in the HD group only (p < 0.05). Net amino acid balance across the leg improved in both groups, but a net anabolic effect was observed only in the HD group (p < 0.05). CONCLUSIONS/INTERPRETATION: We conclude that supraphysiological hyperinsulinaemia is necessary to stimulate muscle protein synthesis and anabolic signalling in healthy older individuals, suggesting the existence of a true age-related insulin resistance of muscle protein metabolism.

Resistive exercise blunts LPS-stimulated TNF-alpha and Il-1 beta.

To examine the influence of acute resistive exercise and "hormone status" on cytokine profile, 35 postmenopausal women (72 +/- 6.2 yr) underwent a moderate-high-intensity resistive exercise bout or rested. There were 4 groups: no hormone replacement (NHR, n = 9), hormone replacement (HRT, n = 12), selective estrogen receptor modulator (SER, n = 7), or resting control (no hormone replacement, CON, n = 7). NHR, HRT, and SER exercised (3 sets, 10 exercises @ 80 % 1RM). Blood was collected pre-exercise (PR), postexercise (PO), and two hours (2H) postexercise (same times for CON). Blood was diluted 1 : 10 in culture medium and incubated (37 degrees C, 5 % CO2, 24 h) with lipopolysaccharide (LPS, 25 microg . ml (-1)). Serum and supernatant from LPS-stimulated blood were analyzed for IL-6, IL-1 beta, and TNF-alpha using ELISA. Resistive exercise increased PO serum IL-6, and PO LPS-stimulated IL-6 and IL-1 beta in the exercise groups (HRT, NHR, SER collapsed; EX, n = 28). LPS-stimulated IL-1 beta remained elevated at 2H in EX and was significantly higher than PR in CON at 2H. Expressed per monocyte, EX had significantly lower IL-1 beta and TNF-alpha LPS-stimulated production at PO and 2H compared to CON, indicating an exercise-induced blunting of an apparent diurnal response on cytokine production. In postmenopausal women, acute resistive exercise increased circulating IL-6, but reversed an apparent diurnal increase in LPS-stimulated IL-1 beta and TNF-alpha production with no influence of hormone replacement or raloxifene.