Proceedings of The Physiological Society

The Biomedical Basis of Elite Performance 2016 (London, UK) (2016) Proc Physiol Soc 35, C05

Oral Communications

Beta-adrenergic agonist, Ractopamine, increases skeletal muscle expression of enzymes involved in the biosynthesis of anabolic intermediates

D. Brown1, H. Williams1,2, K. Ryan1,3, T. Wilson4, D. Harris4, M. Mareko1,5, Z. Daniel1, S. Jones1, R. Emes6, J. Wattis2, I. Dryden2, C. Hodgman1, T. Parr1, J. Brameld1

1. School of Biosciences, University of Nottingham, Nottingham, United Kingdom. 2. Mathematical Sciences, University of Nottingham, Nottingham, United Kingdom. 3. Guys Hospital, London, United Kingdom. 4. VMRD Global Therapeutics, Zoetis, Kalamazoo, Michigan, United States. 5. Botswana College of Agriculture, Gaborone, Botswana. 6. Veterinary Medicine and Science, University of Nottingham, Nottingham, United Kingdom.

  • Fig. 1. Effects of beta-adrenergic agonist (BA) and Growth Hormone (GH) treatment for 1, 3, 7, 13 or 27 days on gene and protein expression in LD muscle (relative to control cohort (C)). A-F show mRNA expression of A. MyHC IIA (myh2); B. MyHC IIB (myh4); C. Phgdh; D. Psat1; E. Psph; and F. Pck2. G and H show protein expression of PEPCK-M and PHGDH in LD muscle on days 3 and 7 respectively. * P<0.001 for treatment. # P<0.001 for treatment-time interaction.

Manipulation of muscle mass has implications for sporting performance as well as potential health benefits. This study sought to investigate the mechanisms by which Beta-adrenergic agonists (BA) and Growth Hormone (GH) mediate their muscle hypertrophy effects, through the examination of changes in the skeletal muscle transcriptome during treatment of pigs with these anabolic agents over a 27 day timecourse. Female pigs (85 kg) were all fed a high protein/ energy diet ad-libitum, with the GH group receiving an intramuscular injection of porcine GH (10mg, Reporcin, Zamira, Australia) every other day, the BA group receiving Ractopamine (Eli Lilly, USA) at 20mg/kg feed, and the control group (C) simply had ad-libitum feed. Pigs were killed by exsanguination (following electrical stunning) after 1, 3, 7, 13 and 27 days of treatment (n=10 per treatment per time point, n=15 on day 27) and samples of the Longissimus dorsi (LD) muscle were collected. All animal work was done in accordance with UK Home Office regulations. The effect of treatments on the LD transcriptome was assessed using the Agilent pig microarray followed by gene cluster analysis using a modified maSigPro methodology (Conesa et al., 2006). Verification of differentially expressed genes and proteins in LD was by quantitative RT-PCR and western blotting, respectively and assessed by two-way or one-way ANOVA, respectively. BA, but not GH, significantly (P<0.05) increased muscle weights (semitendinosis: BA 529±63g vs GH 498±95g vs C 474±67g) and induced a switch to faster muscle fibre types, with expression of MyHC IIB (myh4) and MyHC IIA (myh2) mRNA being up and down-regulated respectively (Fig. 1A and 1B). MaSigPro clustering of microarray data revealed extensive coordinated up-regulation of genes involved in the serine synthesis pathway, phosphoglycerate dehydrogenase (Phgdh), phosphoserine-aminotransferase (Psat1) and phosphoserine phosphatase (Psph), by BA and to a lesser extent GH (P<0.001; Fig. 1C-E). This was accompanied by elevated PHGDH protein at days 3 and 7 (P<0.05; Fig. 1G and 1H). In addition, clusters included mitochondrial phosphoenol pyruvate carboxykinase (PEPCK-M) transcripts (Pck2), which was similarly increased by BA treatment (P<0.001; Fig. 1F), and there was a 2-fold increase in PEPCK-M protein at day 7 (P<0.001; Fig. 1H). BA treated pigs exhibit increased expression of PHGDH and PEPCK-M in skeletal muscle undergoing accelerated growth. These enzymes are known to regulate flux of glucose carbons into biosynthetic pathways for the generation of anabolic intermediates (Vincent et al., 2015), particularly in cancer cells. We are now exploring the role of PHGDH and PEPCK-M in modulating a muscle anabolic response.

Where applicable, experiments conform with Society ethical requirements