A: representative tension tracing in guinea pig tracheal rings after an acetylcholine (EC50) contraction followed by increasing concentrations of the β-adrenoceptor agonist isoproterenol in the presence of oleic acid (20 μM), linoleic acid (20 μM), GW9508 (20 μM), or their vehicle (0.1% DMSO). B: isoproterenol concentration-response relaxation curves in the presence of vehicle (0.1% DMSO) or oleic acid (20 μM; n = 8), linoleic acid (20 μM; n = 7), or GW9508 (20 μM; n = 6). C: EC50 value of isoproterenol-induced relaxation of an acetylcholine (EC50) contraction in the presence of oleic acid (20 μM; n = 8), linoleic acid (20 μM; n = 7), or GW9508 (20 μM; n = 6) compared with vehicle (0.1% DMSO). D: muscle force remaining after isoproterenol (10−8.5 M)-induced relaxation of acetylcholine (EC50) contraction in the presence of oleic acid (20 μM; n = 8), linoleic acid (20 μM; n = 7), or GW9508 (20 μM; n = 6) compared with vehicle control.