Zinc methionine alters muscle and adipose gene expression and protein concentration of calf-fed Holstein steers fed zilpaterol hydrochloride

Abstract Text: Zinc (Zn) has been shown to have allosteric binding sites on β2-adrenergic receptors (β-AR), enhancing agonist affinity, and inhibiting antagonist binding.  Therefore, our objective was to determine the effect of supplementing a Zn methionine complex (ZINPRO^®) during the last 115 d of feed, when zilpaterol hydrochloride (ZH) is fed for the final 20 d, with a 3-d withdrawal prior to slaughter on muscle and adipose tissue gene expression and protein concentration of calf-fed Holstein steers.  Steers (n = 211; initial BW = 468.5 ± 0.5 kg) were blocked by weight and randomly assigned to pens and treatment: 1) Control; ZnSO₄ added to provide 90 ppm Zn, and 2) ZINPRO; 720 mg Zn/hd/d provided by ZINPRO at the time of terminal implant.  Steers were harvested at a commercial abattoir, and 20 steers per treatment were randomly selected for semimembranosus muscle and adipose tissue biochemical analysis.  Messenger RNA and protein was isolated from the muscle and adipose tissue for RT-QPCR, western blotting, and myosin analysis.  Using RT-QPCR analysis, genes of interest included AMPKα, β1AR, β2AR, β3AR, MHC-I, MHC-IIA, MHC-IIX, GPR43, GPR41, Glut4, SCD, CEBPβ, and PPARγ.  No differences (P > 0.05) were detected in muscle tissue mRNA abundance between treatments for AMPKα, MHC-IIA, β2AR, β3AR, GPR43, GPR41, Glut4, and CEBPβ.  ZINPRO fed cattle had an increased quantity of MHC-I mRNA (P < 0.05) in muscle tissue.  Control cattle had an increased quantity of MHC-IIX, β1AR, PPARγ and SCD mRNA (P < 0.05) in muscle tissue.  In adipose tissue, Control cattle had an increased quantity of Glut4 mRNA (P < 0.05).  There were no differences (P > 0.05) between treatments for AMPKα, β2AR, GPR43, GPR41, SCD, CEBPβ, and PPARγ mRNA in adipose tissue.  Protein quantification for muscle and adipose tissue was performed via western blotting procedures to assess the abundance of the β1AR, β2AR and β3AR; however, no differences (P > 0.05) were detected between treatments.  Muscle protein was also run on acrylamide gels to separate MHC-I and II; ZINPRO fed cattle had a greater concentration of MHC-II protein (P > 0.05).  These results indicate that ZINPRO and ZH in combination increases MHC-I, decreases MHC-IIX gene expression, and increases myosin protein concentration in skeletal muscle.

Keywords: Myosin heavy chain, zilpaterol hydrochloride, zinc methionine