Six opioid peptides, like morphine, were found to produce dose-dependent contractions of dog isolated intestine when administered as intraarterial boluses. The increases in incidence and amplitude of intestinal contractions were antagonized by naloxone. The rank order of potency of the opioid agonists tested was D-Ala2-met-enkephalinamide > D-Ala2-leu-enkephalinamide > met-enkephalin > β-endorphin 1-31 > morphine ≥ morphiceptin > dynorphin 1-13. The contractions induced by two opioid agonists displayed differential sensitivity to blockade by tetrodotoxin (TTX). Met-enkephalin was barely affected by concentrations of TTX that markedly reduced responses to morphiceptin. Some portion of the motility effect of met-enkephalin may be exerted directly on intestinal smooth muscle.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Pharmacology, Toxicology and Pharmaceutics(all)