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

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

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Beta-Adrenergic Receptor Agonists
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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 GF by 15-17
  and 17-18 (Laudert et al., 2004Gruber et al.,
  2007)

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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

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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
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Beta-Adrenergic Receptors Cont

• 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

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Biocarta
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http//web.indstate.edu/thcme/mwking
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Summary

• Ractopamine hydrochloride is a beta-agonist that
  works via the ß-AR
• Activation of the ß-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