To inherit your mother's dimples or father's blue eyes may be considered genetic luck. But not all hereditary traits are desirable. Just ask any of the more than 500 college students interviewed by health psychologist Christopher France over the last few years. Everyone in this group has at least one parent with high blood pressure, meaning they are twice as likely to develop the condition themselves. 

France's studies have focused on a shared trait between people who have hypertension and their kids who don't. Scientists have long known that high blood pressure patients have a decreased pain sensitivity, a condition they assumed was a side effect of hypertension. But in his studies of the offspring of hypertensives, France found that some people in this high-risk group also are less sensitive to pain, suggesting that this symptom isn't a result of hypertension - instead, it may indicate the onset of the disorder. ("On the Trail of a Silent Killer," Perspectives, Autumn/Winter 1997) 

France has been conducting research in this area for more than a decade, with much of his research support coming from the American Heart Association. A new, four-year $1.3 million award from the National Institutes of Health will allow him to test the hypothesis he's conceived from his earlier studies. This international project is designed to figure out what causes the decreased sensitivity to pain. 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.

When the body is hurt, the brain releases chemicals called opioids to dull the sensation of pain. When enough chemicals are in the blood, 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 involve people who have a parent with hypertension. The third site will include people recently diagnosed with high blood pressure who are receiving treatment 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 or more after receiving the medication, says 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 the researchers will have identified the pain perception problem. 

France and his collaborators will monitor changes in pain perception alongside changes in blood pressure in study participants throughout the following three years, 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. 

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."

Kelli Whitlock is the editor of Perspectives.

For more information about this project, e-mail Christopher France.