Control of neurotransmission by prostaglandins in canine trachealis smooth muscle

Contractile responses of canine tracheal smooth muscle to electrical field stimulation diminished over a 2-h period of incubation. However, addition of indomethacin (10^-5 M) for a similar time not only prevented this inhibition of contractile response, but actually markedly increased the response to electrical field stimulation, suggesting that prostaglandins were responsible for the time-dependent inhibition. Measured prostaglandin E₂ increased in the tissue bath over 2 h in control tissues. Addition of prostaglandin E₂ to the tissue produced similar inhibition of contractile responses to electrical field stimulation in a concentration-dependent manner. In contrast, incubation alone, treatment with indomethacin, or addition of prostaglandin E₂ had little, if any, effect on contractions induced by acetylcholine. We conclude that the release of prostaglandins from canine tracheal smooth muscle that occurs with time has a predominantly inhibitory effect on cholinergic neurotransmission at a prejunctional site.