Beta-endorphin levels spiked temporarily in painful heart attacks but stayed flat in painless ones, while met-enkephalin and dynorphin remained unchanged in both.
28 patients, 2 groups12 painless vs 16 painful heart attacks tracked over 4 days — only beta-endorphin responded, and only to pain
What the researchers 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.
Why it 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.
How the study worked
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.
What this study cannot 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.
How to read the evidence
Moderate — a cross-sectional study with clear group comparisons and multiple time points, but small sample sizes and observational design limit causal conclusions.
When this study was published
Published in 1992 (34 years ago). The finding that beta-endorphin correlates with cardiac pain remains clinically relevant.
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.
Questions still open
- 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?
Common questions
Why are some heart attacks painless?
What is beta-endorphin?
Read the original research
Plasma endogenous opioid levels in acute myocardial infarction patients, with and without pain.
European heart journal, 13(8), 1074-9
Citation
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.