Effects of an enkephalin analog on motility of the small and large intestine in the cat.

In order to study the effects of naturally occurring opioids on intestinal motility we exposed the unanesthetized cat to different doses of methionine (Met)-enkephalin analog DAMME. DAMME 10(-10) and 10(-9) M/kg body weight inhibited spike activity in the small intestine 20-50 min after injection, whereas in the colon doses as low as 10(-11) M/kg stimulated spiking. Transit of a radiopaque marker infused into duodenal and cecal catheters was delayed both in the small and large bowel. The enkephalin effect was inhibited by the opiate antagonist naloxone 10(-8) and 10(-7) M/kg in the colon, but only at 10(-7) M/kg in the small intestine. Atropine suppressed the enkephalin effect in the small, but not in the large bowel. DAMME caused central nervous side effects. It is concluded that the Met-enkephalin analog suppresses myoelectrical activity in the small intestine probably via cholinergic nervous pathways, and it stimulates spiking and segmenting contractions in the colon probably via a myogenic action. Opiate antagonists may be useful in the treatment of constipation if endogenous opioids are involved.