Exogenous but not endogenous PGE2 modulates pony tracheal smooth muscle contractions

The modulatory role of prostaglandin E2 (PGE2) was examined in pony tracheal smooth muscle strips. Although exogenous PGE2 inhibited the contractile response to both electrical field stimulation (EFS) and acetylcholine (ACh) in a dose-dependent manner, the concentration required to inhibit the response to EFS (10 nM) was less than that required to inhibit the response to ACh (0.1 microM). Cyclooxygenase inhibition with aspirin or meclofenamate had no effect on either the response to EFS or to ACh even though PGE2 production was inhibited. Our results demonstrate that in ponies as in other species, exogenous PGE2 can inhibit the airway smooth muscle's response to EFS and ACh. However, the failure of cyclooxygenase inhibition to alter the response to EFS and ACh suggests that endogenous prostanoids do not exert a significant modulatory effect on pony tracheal smooth muscle in vitro.