Inhibition by enkephalins of peristaltic activity of the rabbit ileum and its reversal by naloxone.

Two pentapeptides, the enkephalins have been isolated and identified from the mammalian gastrointestinal tract and have been shown to be potent opiate agonists (Hughes 1975; Lord et al 1977; Hughes et al 1977). Further work has demonstrated that methionine (met-)-enkephalin and D-Ala2-Leu-enkephalinamide affected the peristaltic reflex of the guinea-pig isolated ileum (van Nueten et al 1977; Kromer et al 1980). On the other hand, the rabbit isolated ileum has been scarcely used as model to study the peristaltic reflex (Feldberg & Lin 1949; Beleslin et al 1978). However, after evidence of the existence of met- and leucine (leu)-enkephalin as well as of enkephalin receptors in the rabbit intestine was reported (Hughes et al 1977; Oka 1980) it became interesting to investigate the action of enkephalins on the peristaltic activity of rabbit isolated ileum.