January 11, 2012

Exercise Pill Protects Against Heat Sensitivity

(Ivanhoe Newswire) -- A young fit athlete who appears no different from the others on his football team dies suddenly during practice on a hot summer day. What could make this happen? According to new studies some physically fit young people could have a genetic mutation that makes them more sensitive to heat. Researchers led by those at Baylor College of Medicine may have identified a molecule that could reduce that threat.

Dr. Susan Hamilton chair of molecular physiology and biophysics at BCM, studies the ryanodine receptor 1(RyR1) which is linked to a deadly disorder called malignant hyperthermia. People with this disorder suffer a life-threatening rise of temperature when given a certain kind of general anesthesia. When mice with this mutation exercise in a hot room or are even exposed for a short time to the temperatures of a hot summer, they demonstrate all the symptoms of malignant hyperthermia before they die. New evidence suggests that this heat sensitivity is also found in humans with comparable RyR1 mutations.

In Hamilton's studies of muscle fatigue her and her colleagues studied a compound called AICAR which slows muscle fatigue and improve muscle endurance without exercise —known as "exercise in a pill," said Hamilton.

"When we gave AICAR to the (heat-sensitive) mice, it was 100 percent effective in preventing heat-induced deaths, even when we gave it no more than 10 minutes before the activity," Hamilton was quoted as saying.

Further experiments showed that one target of AICAR is the skeletal muscle calcium release channel, RyR1. "AICAR stops the feed forward cycle that triggers these sustained muscle contractions," Hamilton was quoted as saying.

"It also protects intracellular calcium stores from depletion and this contributes to the ability of this compound to slow muscle fatigue."

The finding gives hope for young athletes and soldiers with abnormal heat sensitivity, especially those who must wear heavy gear that does not allow them to expend the heat generated with exercise.

"We were attempting to identify an intervention, something that could be used prophylactically to protect these sensitive individuals without significant side effects," Hamilton was quoted as saying.

More research is needed before Hamilton can determine if AICAR is useable, but the studies in mice are encouraging.

SOURCE: Nature Medicine, January 8, 2012