ATLANTA -- ACE inhibitors can keep high blood pressure under control if life is running smoothly, but they don't prevent it from rising when things get tense -- like when the bottom drops out of the stock market. That's when a person needs a friend.
And if a human friend isn't available, the four-legged variety will do nicely, a study of responses to stress in a group of hypertensive New York City stockbrokers conducted by University at Buffalo researchers, has shown.
Findings were presented here today (Nov. 7) at the American Heart Association annual meeting.
Karen Allen, Ph.D., UB research assistant professor of medicine, assessed the effect of social support on heart rate, blood pressure and renin reactivity in response to mental stress in a group of 48 stockbrokers, all of whom were being treated with lisinopril, an angiotensin converting enzyme (ACE) inhibitor used to treat hypertension.
She found that in 24 participants selected at random to add a dog or cat to their treatment regimen, these cardiovascular measures remained significantly more stable during stressful situations than in 24 participants in the non-pet-owner group, who served as controls.
"When we told the group that didn't have pets about the findings, many went out and got them," Allen said. "Social support is what I'm interested in," she added. "This study shows that if you have high blood pressure, a pet is very good for you when you're under stress, and pet ownership is especially good for you if you have a limited support system." All of the study participants had lived alone for more than five years.
Allen has shown in previous studies that a loved pet can exert a calming influence on blood pressure and heart rate when the owner is performing standard tasks designed to induce mental and physical stress. Her research also has shown that pet ownership can substitute for human companionship and provide physiological benefits similar to that of friends for older women who live alone, often in isolation.
Those earlier studies compared existing pet owners with non-pet owners. This is the first study to assess hypertensive subjects before and after acquiring a pet, and to assign participants randomly to pet ownership or to a control group.
The study group was composed of 24 male and 24 female stockbrokers in New York City who had pre-treatment blood-pressure readings higher than 140/90 hg/ml. All were non-smoking college graduates with no other medical conditions, lived alone and had not owned a pet in the previous five years. All participants had to be willing to acquire their choice of a dog or a cat if assigned to the control group.
Blood pressure, heart rate and activity of plasma renin -- an enzyme that increases in response to stress -- were measured in all subjects before drug therapy began, and six months later when all were taking ACE inhibitors and those in the test group had acquired their pets. Measurements were taken in a physician's office after 15 minutes of rest and in participants' homes.
The home measurements were taken after an initial 15-minute rest period, once a minute during each of two five-minute stress tests and after a 15-minute rest period between tests. Stress tests involved performing mental arithmetic and giving a speech. Participants assigned to pet ownership had their dog or cat with them during the tests.
Results showed that before treatment with ACE inhibitors, the average resting blood pressure was 160/104. ACE-inhibitor therapy lowered it to an average of 123/83. Before treatment, the stress tests created, on average, the following increases: heart rate -- 21 beats per minute; systolic blood pressure -- 18 mm/Hg; diastolic blood pressure -- 18mm/Hg, and renin of 3.9 nanograms/ml/hr.
Six months later, when all participants were receiving ACE inhibitors, during stress the non-pet-owners' heart rate, blood pressure and renin increased nearly to pre-treatment levels. Pet owners, in contrast, showed increases in heart rate of 10 beats per minute; systolic blood pressure of 8 mm/Hg; diastolic blood pressure of 9 mm/Hg and renin activity of 1.6ng/ml/hr.
Joseph L. Izzo, Jr., M.D., UB professor of medicine, and Barbara E. Shykoff, Ph.D., research assistant professor of medicine, also contributed to this study. Allen conducted the research as a Waltham Research Fellow, funded by the Waltham Research Center for Pet Nutrition located near London, England.
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