Opioid Peptides Raised Levels of a Heart Hormone That Controls Blood Pressure
Morphine and opioid peptides increased plasma atrial natriuretic peptide (ANP) — a heart hormone that lowers blood pressure and promotes fluid loss.
Quick Facts
What This Study Found
Morphine injected into the brain (intracerebroventricular) was 10 times more potent than intravenous morphine at increasing plasma ANP (atrial natriuretic peptide), a hormone released by the heart that lowers blood pressure and promotes sodium excretion.
Leu-enkephalin decreased plasma ANP concentrations, the opposite effect of morphine.
Dynorphin and beta-endorphin (given either into the brain or into the vein) did not change ANP levels at all.
All four opioids increased plasma norepinephrine and epinephrine (stress hormones), but morphine caused increases 10 to 50 times greater than the others.
Ganglionic blockade (cutting the nerve connection from the brain to the heart) significantly reduced morphine's ability to increase ANP, confirming the effect requires an intact autonomic nervous system.
Key Numbers
How They Did This
Awake, freely moving Sprague-Dawley rats received intracerebroventricular or intravenous injections of morphine, leu-enkephalin, dynorphin, or beta-endorphin. Plasma ANP and catecholamines (norepinephrine, epinephrine) were measured by radioimmunoassay before and after injection. Ganglionic blockade with chlorisondamine tested the role of the autonomic nervous system.
Why This Research Matters
This showed that different opioids have very different effects on cardiovascular hormones. Morphine increases ANP (which lowers blood pressure), while enkephalin decreases it. This may partly explain why morphine lowers blood pressure and has specific cardiovascular effects distinct from other opioids.
The Bigger Picture
The connection between brain opioid receptors and heart ANP release adds another dimension to understanding blood pressure regulation and may explain some cardiovascular effects of opioid drugs.
What This Study Doesn't Tell Us
Tested in rats, not people. Brain injection bypasses normal routes. Only acute single doses were tested. The ganglionic blockade experiment is crude and affects many systems beyond the opioid-ANP pathway.
Questions This Raises
- ?Do chronic opioid users have altered ANP levels?
- ?Could this pathway be used therapeutically for heart failure?
Trust & Context
- Key Stat:
- 10× central vs peripheral potency For morphine-induced ANP release from the heart
- Evidence Grade:
- Preliminary animal study in freely moving rats — physiologically relevant but not confirmed in humans.
- Study Age:
- Published in 1988 — early evidence for opioid-natriuretic peptide crosstalk.
- Original Title:
- Effects of morphine and opioid peptides on plasma levels of atrial natriuretic peptide.
- Published In:
- Life sciences, 43(10), 851-8 (1988)
- Authors:
- Crum, R L, Brown, M R
- Database ID:
- RPEP-00068
Evidence Hierarchy
Tests effects in animals (usually mice or rats), not humans.
What do these levels mean? →Frequently Asked Questions
What is ANP?
Atrial natriuretic peptide — a hormone released by the heart when it is stretched (high blood volume). It lowers blood pressure by promoting salt and water excretion and relaxing blood vessels.
Why does brain opioid stimulation affect the heart?
The brain controls heart function through the autonomic nervous system. Opioid receptors in the brain can trigger signals that change heart rate, blood vessel tone, and ANP release.
Read More on RethinkPeptides
Cite This Study
https://rethinkpeptides.com/research/RPEP-00068APA
Crum, R L; Brown, M R. (1988). Effects of morphine and opioid peptides on plasma levels of atrial natriuretic peptide.. Life sciences, 43(10), 851-8.
MLA
Crum, R L, et al. "Effects of morphine and opioid peptides on plasma levels of atrial natriuretic peptide.." Life sciences, 1988.
RethinkPeptides
RethinkPeptides Research Database. "Effects of morphine and opioid peptides on plasma levels of ..." RPEP-00068. Retrieved from https://rethinkpeptides.com/research/crum-1988-effects-of-morphine-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.