ATHENS, Ohio -- Scientists have long known that people with high blood pressure and those at risk of developing the disorder have a decreased sensitivity to pain. But just how the higher tolerance relates to the onset of hypertension has been a mystery -- one researchers at Ohio University hope to solve during a new four-year study launched this summer.
More than 400 people at three sites will be enrolled in this international project, which is supported by a $1.3 million National Institutes of Health grant. The study could pinpoint one of several possible causes of high blood pressure, information that could give doctors another tool in the prevention of hypertension and may even lead to a new drug to treat some people with the disorder.
The project is being led by Ohio University health psychologist Christopher France, who has examined pain responses in hundreds of people with a family history of high blood pressure. His studies found that participants had an unusually high tolerance for pain, something also seen in hypertensive patients. The problem, France suspects, may be a faulty switch in a part of the brain that controls pain. The fact that this part of the brain, the hypothalamus, also controls blood pressure prompted France to propose this new study.
The first step, he says, is to figure out what causes the decreased pain sensitivity. When the body is hurt, the brain releases chemicals called opioids to dull the sensation of pain. The brain then turns off opioid release. But in people with or at risk for high blood pressure, France suspects the chemical production continues, leading to the decreased pain sensitivity he's noted in his earlier studies.
To confirm this, researchers plan to enroll 144 people at each of three sites: Ohio University, the University of Minnesota and the University of Birmingham in England. Studies in Ohio and Minnesota will examine people who have a parent with hypertension. The third site will study people recently diagnosed with high blood pressure at a clinic in England.
Researchers will temporarily block the activity of these naturally occurring opioids with a drug called naltrexone, then measure participants' responses to electrical impulses. The testing takes about half an hour, and patients will be closely monitored for several hours after receiving the medication and longer if necessary, said John Brose, an Ohio University professor of family medicine who will coordinate physical examinations of study participants at the Athens site before and after testing.
If study participants who felt little or no pain from electronic stimuli before receiving naltrexone report feeling pain when their opioid production is halted, France says they will have identified the pain perception problem.
The next step will come during the three-year follow up portion of the study. France and his collaborators will monitor changes in pain perception alongside changes in blood pressure in study participants throughout the three-year period, looking for a correlation between the two.
"It's possible that what causes decreased pain sensitivity is also involved in the onset of hypertension," suggests France, an associate professor of psychology. "It may be that elevated opioid levels are a common mechanism responsible for high blood pressure."
France hopes the study will help doctors identify which of these high-risk patients may be more likely to develop high blood pressure later in life. A family history is just one of many risk factors for hypertension, and not all people with a family tie to the disorder will experience problems themselves.
"This study is designed to see whether we can find those who are most likely to develop hypertension among a subset of those who are at higher risk," France says. "If we can do that, doctors could prescribe nonpharmacological interventions for those patients early on, such as stress management, diet modification and exercise."
Such advice is healthy for anyone, France admits, as lack of exercise or bad eating habits increases the risk of high blood pressure. "But if you can pinpoint with greater accuracy that a particular individual is more likely to develop this problem, they become more motivated to follow a healthy regimen, and their doctor can follow them more closely for cardiovascular problems."
It's also possible the study's findings could help identify what exactly goes wrong with the hypothalamus' control of opioid production. And if it's discovered that this problem also triggers rising blood pressure, a drug could be developed to target the problem area, France says.
In addition to his physician's role in the project, Brose hopes to use information revealed in the study in other research on hypertension under way through the clinical research program in Ohio University's College of Osteopathic Medicine, which Brose directs.
France and Brose hold appointments in the College of Arts and Sciences and College of Osteopathic Medicine, respectively.
Written by Kelli Whitlock.
Contact: Christopher France, 740-593-1079; france@ohio.edu