Endorphins and other morphine-like substances known as
opioids, which are released during exercise, don't just
make you feel good -- they may also protect you from heart
attacks, according to University of Iowa researchers.
It has long been known that the so-called "runner's
high" is caused by natural opioids that are released
during exercise. However, a UI study, which is published
in the online edition of the American Journal of Physiology's
Heart and Circulatory Physiology, suggests that these
opioids may also be responsible for some of exercise's
Working with rats, UI researchers showed that blocking
the receptors that bind morphine, endorphins and other
opioids eliminates the cardiovascular benefits of exercise.
Moreover, the UI team showed that exercise was associated
with increased expression of several genes involved in
opioid pathways that appear to be critical in protecting
"This is the first evidence linking the natural
opioids produced during exercise to the cardio-protective
effects of exercise," said Eric Dickson, M.D., UI
associate professor and head of emergency medicine in
the Roy J. and Lucille A. Carver College of Medicine and
the study's lead investigator. "We have known for
a long time that exercise is great for the heart. This
study helps us better understand why."
Studies have shown that regular vigorous exercise reduces
the risk of having a heart attack and improves survival
rates following heart attack, even in people with cardiovascular
disease. In addition, exercise also decreases the risk
of atherosclerosis, stroke, osteoporosis and even depression.
However, despite these proven health benefits, much less
is understood about how exercise produces these benefits.
The UI study investigated the idea that the opioids produced
by exercise might have a direct role in cardio-protection.
The researchers compared rats that exercised with rats
that did not. As expected, exercised rats sustained significantly
less heart damage from a heart attack than non-exercised
rats. The researchers then showed that blocking opioid
receptors completely eliminated these cardio-protective
effects in exercising rats, suggesting that opioids are
responsible for some of the cardiac benefits of exercise.
The UI team also showed that exercise was associated
with transient increases in expression of several opioid
system genes in heart muscle, and changes in expression
of other genes that are involved in inflammation and cell
death. The researchers plan to investigate whether these
altered gene expression patterns reveal specific cardio-protective
A better understanding of how exercise protects the heart
may eventually allow scientists to harness these protective
effects for patients with decreased mobility.
"Hopefully this study will move us closer to developing
therapies that mimic the benefits of exercise," Dickson
said. "It also serves as a reminder of how important
it is to get out and exercise every day."