Why Some Heart Attacks Are Painless: The Role of Natural Opioid Levels
Beta-endorphin levels spiked temporarily in painful heart attacks but stayed flat in painless ones, while met-enkephalin and dynorphin remained unchanged in both.
Quick Facts
What This Study Found
Transient plasma beta-endorphin elevation in painful AMI (Group II, n=16) that normalized when pain ceased. No changes in painless AMI (Group I, n=12). Met-enkephalin and dynorphin unchanged in both.
Key Numbers
How They Did This
Blood samples from AMI patients collected on admission (1-3 hours post-MI), at 7, 12, 24 hours, and at 2, 3, 4 days. Beta-endorphin, met-enkephalin, and dynorphin measured by immunoassay.
Why This Research Matters
This study separates the body's opioid response to pain from the heart damage itself. It also raises the question of whether the lack of a beta-endorphin response contributes to the phenomenon of silent heart attacks.
The Bigger Picture
Silent heart attacks are dangerous because people don't seek help. This study suggests the beta-endorphin response is linked to pain perception, not heart damage itself — which could help explain why some people have no warning signs during a heart attack.
What This Study Doesn't Tell Us
Observational study with relatively small groups. Blood opioid levels may not reflect brain or cardiac tissue levels. Cannot determine if opioid differences cause or result from painless MI.
Questions This Raises
- ?Do people who have silent heart attacks have a naturally higher opioid tone that masks pain?
- ?Could beta-endorphin levels be used as a pain biomarker in cardiac care?
Trust & Context
- Key Stat:
- 28 patients, 2 groups 12 painless vs 16 painful heart attacks tracked over 4 days — only beta-endorphin responded, and only to pain
- Evidence Grade:
- Moderate — a cross-sectional study with clear group comparisons and multiple time points, but small sample sizes and observational design limit causal conclusions.
- Study Age:
- Published in 1992 (34 years ago). The finding that beta-endorphin correlates with cardiac pain remains clinically relevant.
- Original Title:
- Plasma endogenous opioid levels in acute myocardial infarction patients, with and without pain.
- Published In:
- European heart journal, 13(8), 1074-9 (1992)
- Authors:
- Bernardi, P(8), Fontana, F(8), Pich, E M(4), Spampinato, S, Canossa, M
- Database ID:
- RPEP-00223
Evidence Hierarchy
A snapshot of a population at one point in time.
What do these levels mean? →Frequently Asked Questions
Why are some heart attacks painless?
This study suggests it may relate to differences in the body's natural opioid response. Patients with painful heart attacks had elevated beta-endorphin, while painless heart attack patients did not — possibly indicating their opioid system responded differently to cardiac injury.
What is beta-endorphin?
Beta-endorphin is one of the body's natural painkillers, released during stress and injury. In this study, it rose only in heart attack patients who felt pain, suggesting it's responding to the pain experience rather than the heart damage itself.
Read More on RethinkPeptides
Cite This Study
https://rethinkpeptides.com/research/RPEP-00223APA
Bernardi, P; Fontana, F; Pich, E M; Spampinato, S; Canossa, M. (1992). Plasma endogenous opioid levels in acute myocardial infarction patients, with and without pain.. European heart journal, 13(8), 1074-9.
MLA
Bernardi, P, et al. "Plasma endogenous opioid levels in acute myocardial infarction patients, with and without pain.." European heart journal, 1992.
RethinkPeptides
RethinkPeptides Research Database. "Plasma endogenous opioid levels in acute myocardial infarcti..." RPEP-00223. Retrieved from https://rethinkpeptides.com/research/bernardi-1992-plasma-endogenous-opioid-levels
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.