Leptin helps regulate body weight and metabolism, but also can affect the heart and blood vessels. The Hopkins researchers studied leptin's effects in a mouse model of obesity that also develops left ventricular hypertrophy (LVH), a condition in which the main pumping chamber of the heart expands and stiffens, preventing proper blood flow to the body. Hypertrophy, which results from stress on the heart (for example, through high blood pressure or obesity), starts off as a compensatory mechanism but soon runs out of control, says lead study author Lili A. Barouch, M.D., an assistant professor of medicine. As the heart muscle is worked harder, it bulks up. But after too much strain, it can become stiff and cease contracting.

In their two-part study, Barouch and colleagues compared the hearts of three groups of mice at 2, 4, and 6 months old. One group lacked the gene for leptin, one group lacked the receptor for leptin, and the third was normal. Progressive obesity developed in the mice lacking leptin or its receptor, and by 6 months of age, researchers observed LVH in these mice but not in the controls. Individual heart cells also showed signs of enlargement.

Next, the Hopkins team divided the 6-month-old obese mice into three groups. Two groups were assigned to lose weight (one by leptin infusions and one by a calorie-restricted diet), while the third group continued to eat its regular diet. After four to six weeks, mice in both diet groups lost the same amount of weight. However, the mice who received leptin infusions had a complete reversal of LVH and a partial shrinkage of enlarged heart cells, whereas the mice on caloric restriction had no chan
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Contact: Karen Blum
kblum@jhmi.edu
410-955-1534
Johns Hopkins Medical Institutions
12-Aug-2003