The role of prostaglandins in the spontaneous and cholinergic nerve-mediated motility of guinea-pig gastric muscle.

The role of PGE1, PGE2 and PGF2 alpha in the spontaneous and cholinergic nerve-mediated motility of guinea-pig gastric muscle strips was investigated. The prostaglandins (PGs) studied induce dose-dependent tonic activation in the longitudinal strips from fundus, corpus and antrum and inhibition of the phasic activity of circular strips from antrum and pyloric sphincter. These effects are not significantly changed in the presence of adrenergic and cholinergic blocking agents nor with tetrodotoxin, and are, therefore, direct effects on the smooth muscle. Indomethacin exerts effects opposite to those of PGs. The contractile responses of the longitudinal and circular smooth muscles to field stimulation (frequency of 10-20 Hz, duration of 0.5 ms and supramaximal voltage) are inhibited by atropine (1 X 10(-6) M), indicating that cholinergic transmission is involved. PGs potentiate the response of the longitudinal muscles but inhibit the response of the circular muscles to field stimulation. On the contrary, indomethacin (1 X 10(-6) to 1 X 10(-5) M) inhibits the response of the longitudinal and potentiates the response of the circular muscles to field stimulation. The data suggest that PGs may exert a negative feedback control over the excitatory transmission in the circular muscle of the guinea-pig stomach.