"Our findings suggest that, in individuals with diabetes, the ability of insulin to lower blood sugar involves the brain," said senior author of the study, Michael Schwartz of the University of Washington at Seattle. "This effect is not trivial; the brain makes a substantial contribution to insulin response."

The findings in rats suggest that therapies that boost the brain response to insulin in patients with diabetes might improve blood sugar control while lowering the required dose of the hormone, the researchers said. That advance, in turn, might help to reduce side effects of insulin treatment, such as weight gain, they added.

Insulin normally allows body tissues, such as the muscles, to take up the blood sugar glucose, the body's prime energy source. In those with diabetes due to a lack of normal insulin or insulin resistance, blood sugar rises, a condition that can lead to tissue damage.

Scientists once thought that insulin's effects were limited to peripheral body tissues that respond to the hormone by importing glucose. However, more recent studies have revealed that insulin receptors in the brain also play an important role in normal blood sugar control.

To extend those findings to the disease state in the current study, the researchers examined the brain's effect on insulin sensitivity in rats with diabetes due to a lack of so-called pancreatic beta cells, which normally secrete insulin. The rats' condition mimics type I, or juvenile, diabetes, a form of the disease that begins in childhood most often due to autoimmune destruction of cells in the pancreas, which leave the organ unable to produce insulin.

The researchers infused the brains of the diabetic rats with a chemical that limits the function of an enzyme involved in the normal
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Contact: Heidi Hardman
hhardman@cell.com
617-397-2879
Cell Press
10-Jan-2006