Background: The loss of skeletal muscle mass that occurs with aging, chronic disease or acute injury is clinically important in the health of humans. The mechanisms relating to the synthesis and breakdown of skeletal muscle are now being intensely investigated. Current studies and possible mechanisms for skeletal muscle protein synthesis and degradation will be reviewed with a specific focus on growth hormone and testosterone. Conclusions:Investigation of the mechanisms of action of growth hormone and testosterone in skeletal muscle will likely lead to new therapies to prevent skeletal muscle loss and new awareness of the importance of skeletal muscle in health and disease.

Wolfe RR: The underappreciated role of muscle in health and disease. Am J Clin Nutr 2006;84:475–482.
Roubenoff R, Castaneda C: Sarcopenia – understanding the dynamics of aging muscle. JAMA 2001;286:1230–1231.
Götherström G, Elbornsson M, Stibrant-Sunnerhagen K, Bengtsson BA, Johannsson G, Svensson J: Ten years of growth hormone (GH) replacement normalizes muscle strength in GH-deficient adults. J Clin Endocrinol Metab 2009;94:809–816.
Schweizer R, Martin DD, Schönau E, Ranke MB: Muscle function improves during growth hormone therapy in short children born small for gestational age: results of a peripheral quantitative computed tomography study on body composition. J Clin Endocrinol Metab 2008;93:2978–2983.
Giannoulis MG, Jackson N, Shojaee-Moradie F, Nair KS, Sonksen PH, Martin FC, Umpleby AM: The effects of growth hormone and/or testosterone on whole body protein kinetics and skeletal muscle gene expression in healthy elderly men: a randomized controlled trial. J Clin Endocrinol Metab 2008;93:3066–3074.
Møller N, Jørgensen JOL: Effects of growth hormone on glucose, lipid, and protein metabolism in human subjects. Endocr Rev 2009;30:152–177.
Hayes VY, Urban RJ, Jiang J, Marcell TJ, Helgeson K, Mauras N: Recombinant human growth hormone and recombinant human insulin-like growth factor I diminish the catabolic effects of hypogonadism in man: metabolic and molecular effects. J Clin Endocrinol Metab 2001;86:2211–2219.
Brill KT, Weltman AL, Gentili A, Patrie JT, Fryburg DA, Hanks JB, Urban RJ, Veldhuis JD: Single and combined effects of growth hormone and testosterone administration on measures of body composition, physical performance, mood, sexual function, bone turnover, and muscle gene expression in healthy older men. J Clin Endocrinol Metab 2002;87:5649–5657.
Kim DS, Itoh E, Iida K, Thorner MO: Growth hormone increases mRNA Levels of PPARdelta and Foxo1 in skeletal muscle of growth hormone deficient lit/lit mice. Endocr J 2009;56:141–147.
Mossberg KA, Masel BE, Gilkison CR, Urban RJ: Aerobic capacity and growth hormone deficiency after traumatic brain injury. J Clin Endocrinol Metab 2008;93:2581–2587.
Emmelot-Vonk MH, Verhaar HJ, Nakhai Pour HR, Aleman A, Lock TM, Bosch JL, Grobbee DE, van der Schouw YT: Effect of testosterone supplementation on functional mobility, cognition, and other parameters in older men: a randomized controlled trial. JAMA 2008;299:39–52.
Henderson GC, Dhatariya K, Ford GC, Klaus KA, Basu R, Rizza RA, Jensen MD, Khosla S, O’Brien P, Nair KS: Higher muscle protein synthesis in women than men across the lifespan, and failure of androgen administration to amend age-related decrements. FASEB J 2009;23:631–641.
Sattler FR, Castaneda-Sceppa C, Binder EF, Schroeder ET, Wang Y, Bhasin S, Kawakubo M, Stewart Y, Yarasheski KE, Ulloor J, Colletti P, Roubenoff R, Azen SP: Testosterone and growth hormone improve body composition and muscle performance in older men. J Clin Endocrinol Metab 2009;94:1991–2001.
Singh R, Bhasin S, Braga M, Artaza JN, Pervin S, Taylor WE, Krishnan V, Sinha SK, Rajavashisth TB, Jasuja R: Regulation of myogenic differentiation by androgens: cross talk between androgen receptor/β-catenin and follistatin/transforming growth factor-β signaling pathways. Endocrinology 2009;150:1259–1268.
Ferrando A, Sheffield-Moore M, Yeckel CW, Gilkison C, Jiang J, Achacosa A, Lieberman SA, Tipton K, Wolfe RR, Urban RJ: Testosterone administration in older men improves muscle function: molecular and physiological mechanisms. Am J Physiol Endocrinol Metab 2002;282:E601–E607.
Ferrando A, Tipton K, Doyle D, Phillips SM, Cortiella J, Wolfe RR: Testosterone injection stimulates net protein synthesis but not tissue amino acid transport. Am J Physiol Endocrinol Metab 1998;275:E864–E871.
Ferrando AA, Sheffield-Moore M, Paddon-Jones D, Wolfe RR, Urban RJ: Differential anabolic effects of testosterone and amino acid feeding in older men. J Clin Endocrinol Metab 2003;88:358–362.
Sheffield-Moore M, Paddon-Jones D, Casperson SL, Gilkison C, Volpi E, Wolf SE, Jiang J, Rosenblatt JI, Urban RJ: Androgen therapy induces muscle protein anabolism in older women. J Clin Endocrinol Metab 2006;91:3844–3849.
Dillon EL, Volpi E, Wolfe RR, Sinha S, Sanford AP, Arrastia CD, Urban RJ, Casperson SL, Paddon-Jones D, Sheffield-Moore M: Amino acid metabolism and inflammatory burden in ovarian cancer patients undergoing intense oncological therapy. Clin Nutr 2007;26:736–743.
You do not currently have access to this content.