Endogenous opioid peptide effects on the guinea-pig biliary tract.
The effects of the endogenous opioid peptides, dynorphin (1-13), Met-enkephalin and beta-endorphin, on contraction induced by transmural stimulation of terminal bile duct preparations (terminal cavity and ampulla) and gallbladder were investigated in vitro. These peptides inhibited ampulla contraction, dose dependently. The potency order, indicated by ID50, was the same as in the guinea-pig ileum, but the absolute ID50 values in the ampulla were lower than in the ileum. In the terminal cavity, the dynorphin (1-13) ID50 was still less than in the ampulla, and beta-endorphin and Met-enkephalin did not reduce contraction by as much as 50%. In the gallbladder, the effects of these opioid peptides on contraction induced by transmural stimulation were not significant. The results suggest differences in the receptor populations of the ampulla and terminal cavity, and lack of opiate receptors (at least micro and k receptors) in the gallbladder.
D000818:Animals; D001659:Biliary Tract / Q000187:drug effects*; D004399:Dynorphins; D004558:Electric Stimulation; D004723:Endorphins / Q000494:pharmacology*; D004744:Enkephalin, Methionine / Q000494:pharmacology; D005704:Gallbladder / Q000187:drug effects; D006168:Guinea Pigs; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D001615:beta-Endorphin
D004723:Endorphins; D004744:Enkephalin, Methionine; D001615:beta-Endorphin; D004399:Dynorphins