Ractopamine (RAC) is fed to livestock to promote muscle mass development, limit fat deposition, and reduce feed consumption; however, it can also cause behavioral effects, including restlessness, agitation, and aggressive behavior. Numerous studies suggest that RAC’s physiological actions begin with its stimulation of β1- and β2-adrenergic receptor–mediated signaling in skeletal muscle and adipose tissue. By use of human cystic fibrosis transmembrane conductance regulator (hCFTR) chloride channels as a sensor for intracellular cAMP, we found that RAC produced concentration-dependent increases in chloride conductance in oocytes coexpressing hCFTR and mouse trace amine–associated receptor 1 (mTAAR1), which was completely reversed by a TAAR1 antagonist. Oocytes coexpressing hCFTR and the human β2-adrenergic receptor (hβ2AR) showed no response to RAC. These studies demonstrate that, contrary to expectations, RAC is not an agonist of the hβ2AR but, rather, a full agonist for mTAAR1.
See article at J Pharmacol Exp Ther 2014, 350:124–129.
- Copyright © 2014 by The American Society for Pharmacology and Experimental Therapeutics