Newswise — A new study in rats is giving researchers hope that more aggressive treatment of hypothyroidism and borderline hypothyroidism will result in a reduction of heart disease in human beings. Because roughly 10 percent of the U.S. population suffers from hypothyroidism or borderline hypothyroidism, the insufficient production of thyroid hormones, the team's discovery could potentially lead to improvement in patients with heart disease.

While further research is needed, results from a recent study entitled, "Low Thyroid Function Leads to Cardiac Atrophy with Chamber Dilation, Impaired Myocardial Blood Flow, Loss of Arterioles, and Severe Systolic Dysfunction," suggest that low thyroid function has the potential to cause heart failure. The study was conducted by the Cardiovascular Research Institute-South Dakota Health Research Foundation, Sioux Valley Health System and The University of South Dakota School of Medicine.

"We provided strong evidence that low thyroid function alone induced in rats eventually can cause heart failure," said Dr. A Martin Gerdes, director of the Cardiovascular Research Institute and co-author of the study. "We also discovered that low thyroid function severely impaired cardiac blood flow due to a dramatic loss of the hearts small blood vessels (arterioles). Within six weeks after inducing low thyroid function in rats, half of the hearts small arterioles were gone."

The effects of hypothyroidism were studied in rats on a short-term (6 weeks) and long-term (1 year) basis. What the research team learned is that hypothyroidism led to severe, progressive contractile dysfunction, chamber enlargement, and ventricular wall thinning despite a reduction in cardiac mass. Hypothyroidism induced in the rats also resulted in impaired myocardial blood flow due to a dramatic loss of arterioles. As a result, the team identified two new mechanisms by which low thyroid function may lead to heart failure.

The study is particularly significant because it was not clear previously if low thyroid function alone can actually cause heart failure or was just another risk factor. "While human data are not yet available, the link between low thyroid function and increased heart disease suggests that something like this could also be occurring in humans," Gerdes said. "Since the rats in this study had relatively mild hypothyroidism, the results suggest that individuals with borderline hypothyroidism may also have similar cardiac changes. Clearly more research is needed to determine if these detrimental cardiac changes occur in humans and if treatment of heart patients with borderline hypothyroidism will lead to improved outcomes." In the absence of further research, however, Gerdes says some caution should be exercised since over treatment with thyroid hormones is known to cause adverse effects.

The Cardiovascular Research Institute (CRI) study is published in the Nov. 15 issue of Circulation, the journal of the American Heart Association. The study can be viewed online at:

About the Research Team and Project Funding

The research was conducted by Yi-Da Tang, M.D., Ph.D., James A Kuzman, Ph.D., Suleman Said, M.S., Brent E. Anderson, B.S., Xuejun Wang, M.D., Ph.D. and A. Martin Gerdes, Ph.D., of the Cardiovascular Research Institute-South Dakota Health Research Foundation and The University of South Dakota School of Medicine.

The Cardiovascular Research Institute is supported by the South Dakota Health Research Foundation, a partnership between The University of South Dakota School of Medicine and Sioux Valley Health System.

This research was supported by grants from the National Center for Research Resources (NCRR) and the National Heart Lung and Blood Institute (NHLBI), two components of the National Institutes of Health (NIH). The research is also supported by the South Dakota 2010 Program.

About The University of South Dakota

Founded in 1862, The University of South Dakota is designated as the only public liberal arts university in the state and is home to a large College of Arts and Sciences, a School of Education and the state's only School of Law, School of Medicine, accredited School of Business and College of Fine Arts. It has an enrollment of approximately 8,600 students taught by 400 faculty members. More information is available at

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Circulation, Nov. 15, 2005 (15-Nov-2005)