Obesity drug takes a different strategy.

A compound that helps the body burn fat may one day become a drug to treat obesity. The compound raises the metabolic rate in rodents by 10 to 30 percent, which would translate into a weight loss of about a half pound per week in humans, says Robert L. Dow of Pfizer in Groton, Conn.

The compound stimulates the beta-3-adrenergic receptor, a protein on fat cells that signals them to break down fat molecules, generating heat (SN: 8/12/95, p. 103). Compounds that work similarly have shown promise in animals but have failed to trigger weight loss in humans. Moreover, those compounds caused unwanted side effects by stimulating two other kinds of beta-adrenergic receptors, one that raises heart rate and another that dilates blood vessels (SN: 5/7/94, p. 303).

The Pfizer scientists shaped the new compound specifically for the beta-3 receptor, reducing its ability to bind to the other two beta receptors. This greater selectivity should also improve the compound's effectiveness in humans, the researchers say.

Unlike weight loss drugs that work by decreasing appetite, a drug that stimulates the beta-3 receptor would get around a problem that afflicts many dieters: The body's metabolism adapts to the lower intake of calories, making it more difficult to lose weight.