Figure 2. Effect of EP₁ receptor activation on ASM contraction and relaxation.

(A) Concentrations of 17-PTP up to 10 μM caused no significant contraction of murine tracheal rings and did not enhance acetylcholine-mediated (Ach) contraction. Data are mean ± SEM of 4 experiments. (B) Pretreatment of tracheal rings with 1 μM 17-PTP for 15 minutes reduced both the potency (EC₅₀ increased) and efficacy of isoproterenol-mediated (Iso) relaxation of tracheal rings contracted with 10 μM acetylcholine. Data are mean ± SEM of 6 experiments. ^†P = 0.001 versus vehicle-treated rings. (C) The inhibitory effect of 17-PTP on isoproterenol-mediated relaxation was also present when the tracheal rings were contracted with 60 mM KCl. Data are mean ± SEM of 8 experiments. *P < 0.05 versus vehicle-treated rings. (D) Pretreatment of tracheal rings with 10 nM PGE₂ evokes desensitization of isoproterenol-mediated relaxation. Data are mean ± SEM of 5 experiments. ^#P < 0.02 versus vehicle-treated rings.