Ractopamine is a trace amine-associated receptor 1 (TAAR1) agonist.¹It increases chloride conductance inX. laevisoocytes expressing the human cystic fibrosis transmembrane conductance regulator (CFTR) and mouse TAAR1 (EC₅₀= 16 µM), an effect that can be blocked by the TAAR1 antagonist EPPTB . It selectively induces chloride conductance in TAAR1- and CFTR-expressing oocytes over those expressing the human β₂-adrenergic receptor (β₂-AR) and CFTR at 36 µM. However, it is also considered a β₂-AR agonist that binds to β₂-ARs (K_i= 0.18 µM for the recombinant human receptor expressed in Sf9 cells) and induces relaxation of isolated guinea pig trachea with an EC₅₀value of 9.1 nM.²Formulations containing ractopamine have been used as food additives in livestock to increase weight gain and leanness and improve feed efficiency.

1.Liu, X., Grandy, D.K., and Janowsky, A.Ractopamine, a livestock feed additive, is a full agonist at trace amine-associated receptor 1J. Pharmacol. Exp. Ther.350(1)124-129(2014) 2.Kern, C., Meyer, T., Droux, S., et al.Synthesis and pharmacological characterization of β2-adrenergic agonist enantiomers: ZilpaterolJ. Med. Chem.52(6)1773-1777(2009)