The effects of non-steroidal anti-inflammatory drugs on cholinergic and histamine-induced contractions of guinea-pig isolated ileum.

1 Eleven non-steroidal anti-inflammatory drugs (NSAID) reversibly inhibited contractions of the longitudinal muscle of the guinea pig isolated ileum induced by acetylcholine, histamine, electrical transmural stimulation and nicotine in this order of increasing potency. 2. After the addition of prostaglandins E1, E2 or F2alpha, with partially effective concentrations of NSAID (but not with higher concentrations which almost totally prevented the responses) the inhibitory effects of NSAID were reversibly lost, except for electrically induced contractions and prostaglandin F2alpha. 3 The effects of NSAID may be due to actions on biological membranes or on distribution of ions in addition to their inhibitory effect on prostaglandin synthesis. Prostaglandins may reverse the inhibition by non-selective sensitization of smooth muscle to various agonists.