Dopamine induced airway smooth muscle relaxation after an acetylcholine EC
contraction in intact guinea pig trachea. Dopamine, in a concentration-dependent manner, relaxes acetylcholine (Ach)-induced contractions in guinea pig tracheal rings. (A) Representative tension tracing in guinea pig tracheal ring illustrating relaxation of Ach (EC50) contraction by dopamine (1 - 100 μM). (B) The effect of cumulative concentration of dopamine (1 - 100 μM) on Ach (EC50)-induced guinea pig tracheal ring contraction. Open circles: dopamine alone. Filled circles: time control. Means ± SEM. *P < 0.05 and **P < 0.01 compared with time control. N = 5.