The role of prostacyclin in modulating cholinergic neurotransmission in guinea‐pig ileum

1 The mechanism of action of prostacyclin (PGI2) on isolated segments of guinea‐pig terminal ileum was studied by recording the changes in isometric tension. 2 In these preparations PGI2 (1 nm‐1 μm) caused a concentration‐dependent increase in muscle tension. This effect was rapid and short‐lasting. 3 PGI2‐induced contractions were inhibited by atropine and potentiated by physostigmine. 4 Hemicholinium‐3 reduced the response to PGI2 and the inhibition was quantitatively comparable at any PGI2 concentration tested. 5 Tetrodotoxin as well as low temperature (20°C) abolished and β‐bungarotoxin reduced the effect of PGI2. 6 Hexamethonium decreased the response to submaximal, but not to maximal PGI2 concentrations. 7 PGI2 potentiated the twitch response of the ileum to electrical stimulation. 8 In the presence of tetrodotoxin, PGI2 did not alter the effect of a sub‐maximal concentration of acetylcholine (ACh). 9 The present results give indirect evidence for the ability of PGI2 to facilitate ACh release from intramural nerves possibly by increasing the excitability of cholinergic cell bodies.