Amino Acid Supplementation Increases Lean Body Mass, Basal Muscle Protein Synthesis, and Insulin-Like Growth Factor-I Expression in Older Women

Abstract Protein has been recognized as an essential nutrient for animals for well over 100 years. Protein plays many important structural and metabolic roles, and some of its component amino acids have additional functions, including as regulatory molecules, as energy substrates and in the synthesis of other non-protein molecules. Skeletal muscle makes up approximately 50% of body weight in horses, with protein being the major non-water component. As an athletic species, the development and maintenance of muscle mass is of the utmost importance in horses. Because muscle mass is largely determined by the balance of rates of muscle protein synthesis and breakdown, understanding how these pathways are regulated and influenced by dietary protein and amino acid provision is essential. Historically, much research regarding protein nutrition in horses has focused on the protein digestibility of different feed ingredients, and the adequacy of different protein sources in supporting the growth and maintenance of horses. This presentation will focus on some of the current areas of active research relating to protein nutrition in horses: the activation of the signaling pathways that regulate muscle protein synthesis, amino acid supplementation in athletic horses, protein metabolism in aged and horses and those with insulin dysregulation, and amino acid and protein nutrition in predominantly forage-fed horses. There are many exciting opportunities for future research in the area of protein and amino acid nutrition in horses across the lifespan.

Download Full-text

Severe diabetes prohibits elevations in muscle protein synthesis after acute resistance exercise in rats

Journal of Applied Physiology ◽

10.1152/jappl.2000.88.1.102 ◽

2000 ◽

Vol 88 (1) ◽

pp. 102-108 ◽

Cited By ~ 41

Author(s):

Mark J. Fedele ◽

Jazmir M. Hernandez ◽

Charles H. Lang ◽

Thomas C. Vary ◽

Scot R. Kimball ◽

...

Keyword(s):

Protein Synthesis ◽

Growth Factor ◽

Resistance Exercise ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Critical Concentration ◽

Diabetic Rats ◽

Insulin Like Growth Factor ◽

Factor I ◽

Growth Factor I

This study determined whether rates of protein synthesis increase after acute resistance exercise in skeletal muscle from severely diabetic rats. Previous studies consistently show that postexercise rates of protein synthesis are elevated in nondiabetic and moderately diabetic rats. Severely diabetic rats performed acute resistance exercise ( n= 8) or remained sedentary ( n = 8). A group of nondiabetic age-matched rats served as controls ( n = 9). Rates of protein synthesis were measured 16 h after exercise. Plasma glucose concentrations were >500 mg/dl in the diabetic rats. Rates of protein synthesis (nmol phenylalanine incorporated ⋅ g muscle−1 ⋅ h−1, means ± SE) were not different between exercised (117 ± 7) and sedentary (106 ± 9) diabetic rats but were significantly ( P < 0.05) lower than in sedentary nondiabetic rats (162 ± 9) and in exercised nondiabetic rats (197 ± 7). Circulating insulin concentrations were 442 ± 65 pM in nondiabetic rats and 53 ± 11 and 72 ± 19 pM in sedentary and exercised diabetic rats, respectively. Plasma insulin-like growth factor I concentrations were reduced by 33% in diabetic rats compared with nondiabetic rats, and there was no difference between exercised and sedentary diabetic rats. Muscle insulin-like growth factor I was not affected by resistance exercise in diabetic rats. The results show that there is a critical concentration of insulin below which rates of protein synthesis begin to decline in vivo. In contrast to previous studies using less diabetic rats, severely diabetic rats cannot increase rates of protein synthesis after acute resistance exercise.

Download Full-text

Short-Term Oxandrolone Administration Stimulates Net Muscle Protein Synthesis in Young Men1

The Journal of Clinical Endocrinology & Metabolism ◽

10.1210/jcem.84.8.5923 ◽

1999 ◽

Vol 84 (8) ◽

pp. 2705-2711 ◽

Cited By ~ 1

Author(s):

Melinda Sheffield-Moore ◽

Randall J. Urban ◽

Steven E. Wolf ◽

J. Jiang ◽

Don H. Catlin ◽

...

Keyword(s):

Skeletal Muscle ◽

Amino Acids ◽

Protein Synthesis ◽

Growth Factor ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Rt Pcr ◽

Short Term ◽

Healthy Men ◽

Factor I

Short term administration of testosterone stimulates net protein synthesis in healthy men. We investigated whether oxandrolone[ Oxandrin (OX)], a synthetic analog of testosterone, would improve net muscle protein synthesis and transport of amino acids across the leg. Six healthy men [22 ± 1 (±se) yr] were studied in the postabsorptive state before and after 5 days of oral OX (15 mg/day). Muscle protein synthesis and breakdown were determined by a three-compartment model using stable isotopic data obtained from femoral arterio-venous sampling and muscle biopsy. The precursor-product method was used to determine muscle protein fractional synthetic rates. Fractional breakdown rates were also directly calculated. Total messenger ribonucleic acid (mRNA) concentrations of skeletal muscle insulin-like growth factor I and androgen receptor (AR) were determined using RT-PCR. Model-derived muscle protein synthesis increased from 53.5 ± 3 to 68.3 ± 5 (mean ± se) nmol/min·100 mL/leg (P < 0.05), whereas protein breakdown was unchanged. Inward transport of amino acids remained unchanged with OX, whereas outward transport decreased (P < 0.05). The fractional synthetic rate increased 44% (P < 0.05) after OX administration, with no change in fractional breakdown rate. Therefore, the net balance between synthesis and breakdown became more positive with both methodologies (P < 0.05) and was not different from zero. Further, RT-PCR showed that OX administration significantly increased mRNA concentrations of skeletal muscle AR without changing insulin-like growth factor I mRNA concentrations. We conclude that short term OX administration stimulated an increase in skeletal muscle protein synthesis and improved intracellular reutilization of amino acids. The mechanism for this stimulation may be related to an OX-induced increase in AR expression in skeletal muscle.

Download Full-text

Response of Muscle Protein Synthesis to the Infusion of Insulin-like Growth Factor-I and Fasting in Young Chickens

Asian-Australasian Journal of Animal Sciences ◽

10.5713/ajas.2002.1760 ◽

2002 ◽

Vol 15 (12) ◽

pp. 1760-1764

Author(s):

K. Kita ◽

T. Shibata ◽

M. Aman Yaman ◽

K. Nagao ◽

J. Okumura

Keyword(s):

Protein Synthesis ◽

Growth Factor ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Insulin Like Growth Factor ◽

Factor I ◽

Growth Factor I

Download Full-text

Differential effect of sepsis on ability of leucine and IGF-I to stimulate muscle translation initiation

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00132.2004 ◽

2004 ◽

Vol 287 (4) ◽

pp. E721-E730 ◽

Cited By ~ 40

Author(s):

Charles H. Lang ◽

Robert A. Frost

Keyword(s):

Skeletal Muscle ◽

Protein Synthesis ◽

Growth Factor ◽

Translation Initiation ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Insulin Like Growth Factor ◽

Factor I ◽

Growth Factor I ◽

Signaling Components

Polymicrobial sepsis impairs skeletal muscle protein synthesis, which results from impairment in translation initiation under basal conditions. The purpose of the present study was to test the hypothesis that sepsis also impairs the anabolic response to amino acids, specifically leucine (Leu). Sepsis was induced by cecal ligation and puncture, and 24 h later, Leu or saline (Sal) was orally administered to septic and time-matched nonseptic rats. The gastrocnemius was removed 20 min later for assessment of protein synthesis and signaling components important in peptide-chain initiation. Oral Leu increased muscle protein synthesis in nonseptic rats. Leu was unable to increase protein synthesis in muscle from septic rats, and synthetic rates remained below those observed in nonseptic + Sal rats. In nonseptic + Leu rats, phosphorylation of eukaryotic initiation factor (eIF)4E-binding protein 1 (4E-BP1) in muscle was markedly increased compared with values from time-matched Sal-treated nonseptic rats. This change was associated with redistribution of eIF4E from the inactive eIF4E·4E-BP1 to the active eIF4E·eIF4G complex. In septic rats, Leu-induced phosphorylation of 4E-BP1 and changes in eIF4E distribution were completely abrogated. Sepsis also antagonized the Leu-induced increase in phosphorylation of S6 kinase 1 and ribosomal protein S6. Sepsis attenuated Leu-induced phosphorylation of mammalian target of rapamycin and eIF4G. The ability of sepsis to inhibit anabolic effects of Leu could not be attributed to differences in plasma concentrations of insulin, insulin-like growth factor I, or Leu between groups. In contrast, the ability of exogenous insulin-like growth factor I to stimulate the same signaling components pertaining to translation initiation was not impaired by sepsis. Hence, sepsis produces a relatively specific Leu resistance in skeletal muscle that impairs the ability of this amino acid to stimulate translation initiation and protein synthesis.

Download Full-text