The contribution of prostaglandins in the muscle of human isolated small intestine to neurogenic responses.

1. In stris cut parallel to the longitudinal or circular muscle, indomethacin (2--10 microgram/ml) usually lowered the tone, thus probably accounting for the reduction of nerve-mediated relaxations to electrical field stimulation. 2. In longitudinal muscle strips, indomethacin enhanced contractions which occurred during electrical stimulation, probably because tone fell, but antagonized after-contractions. By contrast, in the circular muscle indomethacin reduced initial contractions but enhanced after-contractions. 3. Prostaglandin E2 counteracted all of the effects of indomethacin in the longitudinal muscle and most of those in the circular muscle; prostaglandin F2alpha restored circular muscle tone. 4. The results suggest that prostaglandins affect the muscle directly and contribute to the regulation of tone. They may also mediate non-cholinergic contraction in longitudinal muscle and suppress contractility in the circular muscle.