Three opioid peptides caused dose-dependent gallbladder muscle contraction through delta receptors — with met-enkephalin being the most potent.
Delta receptor-mediated contractionOpioid peptides directly contract gallbladder smooth muscle
What the researchers found
Three opioid peptides caused dose-dependent contraction of isolated gallbladder muscle cells: met-enkephalin > dynorphin(1-13) > leu-enkephalin.
The contractions were blocked by the opioid antagonists naloxone and MR2266 but not by muscarinic, CCK/gastrin, or tachykinin antagonists. This confirmed the response was specifically through opioid receptors.
Differential sensitivity to preferential antagonists of mu (naloxone) and kappa (MR2266) receptors, combined with the different potencies of the three agonists, indicated the presence of mu, delta, and kappa opioid receptors on the gallbladder muscle cells.
These opioid peptides are known to be present in myenteric neurons of the gut, providing the natural source of opioid signals for gallbladder muscle.
Why it matters
Opioid receptors on gallbladder muscle explain why opioid drugs can affect biliary function. Opioid-induced biliary spasm (gallbladder contraction causing pain) is a known clinical problem. This study identifies the receptor basis for that side effect.
How the study worked
Smooth muscle cells isolated from canine gallbladder fundus. Contraction measured in response to met-enkephalin, dynorphin(1-13), and leu-enkephalin at various concentrations. Multiple antagonist classes tested to determine receptor specificity.
What this study cannot tell us
Tested in dog gallbladder cells, not human. Isolated cells may behave differently from intact tissue. Only contraction was measured; other gallbladder functions (secretion, relaxation) were not tested.
How to read the evidence
Preliminary in-vitro study on isolated cells — clear pharmacology but removed from whole-organ context.
When this study was published
Published in 1988 — established opioid receptor function in gallbladder smooth muscle.
The bigger picture
Gallbladder motility disorders affect millions. Understanding that opioid peptides directly contract gallbladder muscle through delta receptors could inform treatment of biliary dyskinesia and gallstone disease.
Questions still open
- Do opioid drugs contribute to gallstone formation by altering gallbladder motility?
- Could delta receptor modulation treat biliary disorders?
Common questions
Do opioid pain medications affect the gallbladder?
What is biliary dyskinesia?
Read the original research
Characterization of opioid receptors on isolated canine gallbladder smooth muscle cells.
Life sciences, 42(23), 2373-80
Citation
Severi, C; Grider, J R; Makhlouf, G M. (1988). Characterization of opioid receptors on isolated canine gallbladder smooth muscle cells.. Life sciences, 42(23), 2373-80.