The American Heart Association estimates 50 million Americans have metabolic syndrome. The syndrome is diagnosed when a patient has at least three out of five following medical conditions: abdominal obesity ( "apple" shape rather than "pear" shape), elevated triglyceride levels, low HDL levels (the "good" type of cholesterol), high blood pressure and elevated fasting blood sugar (glucose) levels.

The metabolic syndrome is associated with an accumulation of plaque on the inner walls of the arteries. Thus, patients with the syndrome are at increased risk for heart disease, stroke and other medical complications.

The Metabolic Syndrome, Type 2 Diabetes and PCOS

Two conditions associated with the metabolic syndrome are type 2 diabetes and Polycystic Ovary Syndrome (PCOS). Type 2 diabetes leads to elevated blood sugar levels. It occurs when the pancreas doesn't produce enough insulin or isn't able to make effective use of insulin. The cells of the body need glucose for fuel. Insulin acts like a key to open up the cell walls and allow them to use glucose. When insulin levels are inadequate, glucose doesn't get absorbed. Instead, high levels of the sugar circulate in the blood and the cells are starved for fuel. Over time, this can damage the blood vessel walls and increase the risk for atherosclerosis, organ and tissue damage, nerve disease, blindness and many other complications. Type 2 diabetes is the most common form of diabetes. According to the American Diabetes Association, it affects more than 13 million people in the U.S.

PCOS is a condition characterized by the formation of many small cysts (fluid-filled sacs) on the ovaries. The condition is associated with high levels of androgens (male hormones), menstrual irregularities, acne, infertility and increased hair growth on the face, chest, stomach or back. Women with PCOS are at greater risk for the metabolic syndrome because they tend to gain abdominal weight and have insulin resistance (or type 2 diabetes), high blood pressure and high cholesterol. The Polycystic Ovarian Syndrome Association estimates PCOS may affect 6 to 10 percent of American women.

Studying Metabolic Syndrome: The Power of the Pig

Researchers often use animal models to study human diseases and the effects of potential treatments. Although many different types of animals may be used, pigs are often preferred for metabolic disease research because they are similar to humans in anatomy and physiology.

Scientists at Purdue University are using a breed of pigs called the Ossabaw Island Hogs. These animals come from a small island off the coast of Georgia and are believed to be descendants of Spanish pigs brought to the New World more than 400 years ago. The Island pigs remained isolated from domestic pigs, producing a genetically "pure" strain of hog.

The Ossabaw hogs are unique because they adapted to the island food cycle, having plenty to eat during the fall and facing starvation in the winter. As a result, they learned to overeat in the fall months to store enough fat to carry them over the lean winter months. The adaptive eating behaviors led to the development of low-grade non-insulin resistant (type 2) diabetes in the animals.

In laboratory conditions, Ossabaw hogs that are fed a high-fat, high cholesterol diet respond like humans following a similar diet. The hogs become obese and develop high glucose, high blood pressure and high triglyceride levels. Thus they are an ideal animal model for studying metabolic syndrome.

Rebecca Krisher, Ph.D., Reproductive Physiologist, is studying the Ossabaw hogs as a model for PCOS. She has found the animals fed a high-fat diet gained weight very rapidly, developed abdominal obesity and signs of cysts on their ovaries. Further studies will examine levels of the hormones, estrogen and progesterone to see if they match those in humans with PCOS. Eventually, Krisher is hopeful her research will lead to a better understanding of human PCOS and potential treatments for women with the condition.

Physiologist, Mike Sturek, Ph.D., is using the Ossabaw hogs to study how diabetes and the metabolic syndrome lead to coronary artery disease and other types of vascular disease. He says researchers can test interventional procedures, like angioplasty and stent placement, in the animals and see how they recover. One important discovery is that, compared to humans, the Ossabaw pigs have a propensity to develop restenosis (re-narrowing) of an artery after placement of a stent. This may help scientists understand why humans develop restenosis and test treatments to prevent the problem. Sturek has also found that exercise can decrease the risk of restenosis in the hogs. This suggests that exercise may be beneficial for humans who have received coronary stents as well.

For information about the metabolic syndrome:

American Heart Association

National Heart, Lung and Blood Institute

For information on type 2 diabetes:

American Diabetes Association

National Institute of Diabetes and Digestive and Kidney Diseases

For information on Polycystic Ovary Syndrome:

Polycystic Ovarian Syndrome Association

U.S. Department of Health and Human Services, Office on Women's Health

For general information about animals in research:

The American Physiological Society