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Biochemical basis for the effects of the beta-adrenergic receptor agonist ractopamine hydrochloride in beef cattle

Biochemical basis for the effects of the beta-adrenergic receptor agonist ractopamine hydrochloride in beef cattle. Ractopamine. Repartitioning agent: shifts energy use from fat to muscle deposition

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Biochemical basis for the effects of the beta-adrenergic receptor agonist ractopamine hydrochloride in beef cattle

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  1. Biochemical basis for the effects of the beta-adrenergic receptor agonist ractopamine hydrochloride in beef cattle

  2. Ractopamine • Repartitioning agent: shifts energy use from fat to muscle deposition • Structurally similar to catecholamines and other compounds that bind to the beta-adrenergic receptor

  3. Epinephrine Norepinephrine Dopamine Beta-Adrenergic Receptor Agonists

  4. Ractopamine Hydrochloride • Optaflexx (Elanco Animal Health) approved by FDA in 2003 to feed to cattle at a rate of 70-439 mg/hd/d for last 28-42 d of finishing period • Research suggests 200 mg Optaflexx/d for last 28 d in feedlot improve steer ADG and G:F by 15-17 and 17-18% (Laudert et al.,2004;Gruber et al., 2007)

  5. Agonists and Antagonists • Agonist: Able to bind to receptor and elicit response • Partial agonist: Binds to receptor, but produces only a partial response • Antagonist: Binds to receptor, but does not produce any response, thus blocking signal

  6. Beta-Adrenergic Receptors • Member of G-protein coupled receptor superfamily • 7 transmembrane receptor linked to G-protein • G stimulatory protein (Gs) • Active Gs can bind to adenylate cyclase to activate it Epinephrine

  7. Beta-Adrenergic Receptors Con’t • Adenylate cyclase converts ATP to cAMP • cAMP can activate protein kinase A (PKA) • PKA can phosphorylate proteins in the cell • Phosphorylation of enzymes may cause them to be turned “on” or “off”

  8. Biocarta

  9. http://web.indstate.edu/thcme/mwking

  10. Summary • Ractopamine hydrochloride is a beta-agonist that works via the β-AR • Activation of the β-AR results in production of PKA and phosphorylation of HSL stimulating lipolysis • “Repartitioning” effects of ractopamine due to stimulation of lipolysis and changes in muscle protein metabolism

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