Naloxone Enhanced Delayed Stomach Contractions Triggered by Vagus Nerve
Blocking opioid receptors enhanced delayed stomach contractions from vagus nerve stimulation — kappa agonists (dynorphin-like) were the most effective at suppressing these contractions.
Quick Facts
What This Study Found
Naloxone (100 to 1000 micrograms/kg) did not affect the initial stomach response to vagus nerve stimulation. But it dose-dependently enhanced the delayed response (from vagal afferent fibers). This means endogenous opioids normally restrain the delayed stomach excitation.
Met-enkephalin was markedly more potent than the mu-agonist DAGO and the kappa-agonist dynorphin A(1-13) at inhibiting both types of vagal stomach responses.
The delta-selective agonist DPDPE mimicked met-enkephalin's inhibitory effects. The delta-selective antagonist ICI 174,864 blocked DPDPE's effects. This confirmed delta-opioid receptors mediate the gastric inhibition.
The conclusion: natural opioid peptides (likely enkephalins) tonically restrain vagus nerve-driven stomach excitation through delta receptors.
Key Numbers
How They Did This
Cats had their vagus nerves stimulated electrically. Stomach contractions were measured as gastric pressure changes. Opioid agonists and antagonists were tested systemically. Delta receptor specificity confirmed with selective agonist (DPDPE) and antagonist (ICI 174,864).
Why This Research Matters
The vagus nerve is the main communication line between the brain and gut. Finding that enkephalins through delta receptors control vagal gastric responses reveals how the opioid system fine-tunes digestion. This matters for understanding gut motility disorders and opioid-related digestive side effects.
The Bigger Picture
The vagus nerve is the main communication line between brain and gut. Understanding how opioid peptides modulate vagal control of the stomach is important for treating functional GI disorders.
What This Study Doesn't Tell Us
Tested in cats, not people. Only acute stimulation was studied. The relative contribution of central vs peripheral delta receptors was not separated. Anesthesia likely affected the results.
Questions This Raises
- ?Could selective kappa agonists treat gastroparesis?
- ?Do endogenous opioids contribute to functional dyspepsia?
Trust & Context
- Key Stat:
- Kappa opioids most effective At suppressing vagus nerve-driven stomach contractions
- Evidence Grade:
- Preliminary animal study in cats with systematic receptor comparison.
- Study Age:
- Published in 1988 — important for understanding opioid effects on gastric motility.
- Original Title:
- Effects of naloxone and opioid agonists on gastric excitatory responses to stimulation of the vagus nerve in cats.
- Published In:
- British journal of pharmacology, 95(2), 329-34 (1988)
- Authors:
- Okamoto, T, Kurahashi, K, Fujiwara, M
- Database ID:
- RPEP-00086
Evidence Hierarchy
Tests effects in animals (usually mice or rats), not humans.
What do these levels mean? →Frequently Asked Questions
What is the vagus nerve?
The longest cranial nerve, running from the brain to the abdomen. It controls heart rate, digestion, and many organ functions. It is the main communication highway between the brain and gut.
Why do opioids affect the stomach?
Opioid receptors exist throughout the gut and on the vagus nerve. When activated, they slow stomach emptying and reduce contractions — a major reason opioid drugs cause nausea and delayed digestion.
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Cite This Study
https://rethinkpeptides.com/research/RPEP-00086APA
Okamoto, T; Kurahashi, K; Fujiwara, M. (1988). Effects of naloxone and opioid agonists on gastric excitatory responses to stimulation of the vagus nerve in cats.. British journal of pharmacology, 95(2), 329-34.
MLA
Okamoto, T, et al. "Effects of naloxone and opioid agonists on gastric excitatory responses to stimulation of the vagus nerve in cats.." British journal of pharmacology, 1988.
RethinkPeptides
RethinkPeptides Research Database. "Effects of naloxone and opioid agonists on gastric excitator..." RPEP-00086. Retrieved from https://rethinkpeptides.com/research/okamoto-1988-effects-of-naloxone-and
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkPeptides research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.