Acute testosterone administration does not affect muscle anabolism
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Acute testosterone administration does not affect muscle anabolism David D. Church1, Stefan M. Pasiakos2, Robert R. Wolfe1 and Arny A. Ferrando1*
Abstract We previously demonstrated that improved net muscle protein balance, via enhanced protein synthetic efficiency, occurs 5 days after testosterone (T) administration. Whether the effects of T on muscle protein kinetics occur immediately upon exposure is not known. We investigated the effects of acute T exposure on leg muscle protein kinetics and selected amino acid (AA) transport using the arteriovenous balance model, and direct calculations of mixed-muscle protein fractional synthesis (FSR) and breakdown (FBR) rates. Four healthy men were studied over a 5 h period with and without T (infusion rate, 0.25 mg·min− 1). Muscle protein FSR, FBR, and net protein balance (direct measures and model derived) were not affected by T, despite a significant increases in arterial (p = 0.009) and venous (p = 0.064) free T area under the curve during T infusion. T infusion had minimal effects on AA transport kinetics, affecting only the outward transport and total intracellular rate of appearance of leucine. These data indicate that exposing skeletal muscle to T does not confer immediate effects on AA kinetics or muscle anabolism. There remains an uncertainty as to the earliest discernable effects of T on skeletal muscle protein kinetics after initial administration. Keywords: Testosterone, Amino acids kinetics, Protein metabolism, Stable isotope tracers, Protein synthesis, Protein breakdown
Introduction The effects of exogenous testosterone (T) administration on muscle protein anabolism and lean body mass accrual are well established. The muscle protein kinetic mechanisms through which T administration improves anabolism are less appreciated. Fasted net muscle protein balance is improved in healthy males following a 5d treatment with an oral T analogue [1] or T injection [2]. Muscle protein synthesis (PS) improves with T in fasted muscle of healthy males [1, 2], in part by improving synthetic efficiency, where synthetic efficiency refers to the rate of PS relative to the availablilty of amino acid (AA) precursors. In the post-absorptive state, the essential AA precursors for PS at the whole body level are derived entirely from protein breakdown (PB). In certain tissues and organs, the precursors for PS can be derived from uptake of circulating AA. Improved synthetic efficiency of muscle protein in the post-absorptive state in response to T refers * Correspondence: [email protected] 1 Department of Geriatrics, Donald W. Reynolds Institute on Aging, Center for Translational Research in Aging & Longevity, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA Full list of author information is available at the end of the article
to an increase in the rate of PS relative to the rates of PB and inward AA transport [1, 2]. Greater anabolism is achieved when hyperaminoacidemia accompanies T administration through greater increases i
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