A University study conducted in the Exercise and Environmental Physiology Laboratories has found that histamine receptors may be tied to post-exercise fainting, even among highly trained athletes. Now scientists are following up with long-running research that could give allergy medicine new purpose.
Principal researcher John Halliwill, a human physiology professor at the University, said he has been investigating the connection between exercise and blood pressure since 1993, but “in just the last few years we’ve had some major breakthroughs.”
A 2006 study funded by the American Heart Association revealed that some people who are less hypertensive than normal – that is, they have lower blood pressure – overactivate two histamine receptors usually associated with allergies and acid reflux when they exercise.
“Usually we think about histamine as being related to allergic reactions,” said University Health Center Medical Director Ben Douglas. “This is a new way to look at it.”
While the hypertensive population usually enjoys a positive reaction to exercise, Halliwill explained, those with lower blood pressure “go out and run and get light headed or possibly faint,” even if they are otherwise healthy. Halliwill found that histamine, one of the regular blood pressure mediators, overacts in these people, “serving the need to increase blood flow, which results in a reduction in blood pressure.”
When researchers gave people with low blood pressure allergy antihistamines prior to exercise, their usual post-exertion low blood pressure improved by an average of 80 percent.
“We’ve got something really unique here,” Halliwill said. “We’ve learned how that system behaves, but we’ve actually got a tool to change how the system behaves.”
Halliwill is in the process of conducting a new study in which he pushes his subjects toward loss of consciousness to see if antihistamines still work against low blood pressure.
“We set out to see if we created the worst-case scenario, with dehydration or trying to exercise without moving for a lengthy period of time, to see if it still tips the scale back,” Halliwill said.
Douglas said further research on the topic might allow doctors to prescribe antihistamines to people who faint during exercise.
“Antihistamines as a group are generally very safe medications,” Douglas said. “Some have a history with feeling groggy when they take them, and a small set of people feel more awake … I don’t think there’s a significant consequence for taking them.”
Halliwill said he would be hesitant to let people with lower blood pressure take antihistamines before cardiovascular exercise.
“This normal response that’s there in everybody may be beneficial to us,” Halliwill said. “It may be there for a reason. Currently, we’re trying to understand what that might be.”
Students who wish to volunteer to be subjects in exercise physiology studies should contact the Exercise and Environmental Physiology Laboratories at 541-346-5527.
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