How Gut Neuropeptides Work Together: VIP Triggers Contractions, Dynorphin Shuts Them Down | Research

The takeaway

VIP caused gut muscle contractions through acetylcholine and substance P, but dynorphin and somatostatin completely abolished these contractions.

Complete abolition
Dynorphin at just 100 nM completely blocked VIP-induced gut contractions

What the researchers found

VIP (20 nM-1 microM) induced neurogenic gut contractions via acetylcholine and substance P. Dynorphin (100 nM) and somatostatin (60 nM) abolished these contractions.

Why it matters

This shows how multiple neuropeptides interact in the gut nervous system. Dynorphin's ability to shut down VIP-driven contractions explains part of how opioids cause constipation.

How the study worked

Guinea pig ileal longitudinal muscle strips in organ baths. VIP-induced contractions measured with and without nerve blockers, receptor antagonists, dynorphin, and somatostatin.

What this study cannot tell us

In vitro study in guinea pig gut. Isolated tissue may not reflect intact gut physiology. Species differences in gut pharmacology exist.

How to read the evidence

Preliminary — in vitro study using isolated guinea pig intestinal muscle strips. Clear pharmacological results but removed from intact gut physiology.

When this study was published

Published in 1992 (34 years ago). The role of opioids in gut motility is now well-established and clinically relevant.

The bigger picture

This explains part of why opioid drugs cause constipation — dynorphin and similar opioids shut down the nerve-driven gut contractions that move food along. Understanding these interactions could help develop opioid pain medications with fewer gut side effects.

Questions still open

Can we design opioid pain drugs that don't activate gut dynorphin receptors?
Is dysregulation of the VIP-dynorphin balance involved in irritable bowel syndrome?

Common questions

Why do opioids cause constipation?

This study shows part of the mechanism: dynorphin (a natural opioid) completely shuts down nerve-driven gut contractions. Opioid drugs activate these same pathways, slowing gut movement and causing constipation.

What is VIP?

Vasoactive intestinal polypeptide is a signaling molecule in the gut's nervous system. It triggers muscle contractions that help move food through the intestines, working through acetylcholine and substance P release.

Read the original research

Vasoactive intestinal polypeptide induces neurogenic contraction of guinea-pig ileum. Involvement of acetylcholine and substance P.

Regulatory peptides, 38(2), 155-64

View on PubMed ↗

Citation

Katsoulis, S; Schmidt, W E; Clemens, A; Schwörer, H; Creutzfeldt, W. (1992). Vasoactive intestinal polypeptide induces neurogenic contraction of guinea-pig ileum. Involvement of acetylcholine and substance P.. Regulatory peptides, 38(2), 155-64.