Magazine article Science News

Hormone May Directly Trim Fat from Cells

Magazine article Science News

Hormone May Directly Trim Fat from Cells

Article excerpt

Leptin, a hormone secreted by fat cells, burst into the spotlight in 1995, when investigators found that injections of it could dramatically slim obese and even normal mice (SN: 7/29/95, p. 68).

The simple model proposed at the time was that leptin circulates into the brain and helps regulate food intake. If an animal put on too many pounds, the theory went, its fat cells simply secreted more leptin to reduce the appetite.

Simplicity rarely lasts long in biology.

Leptin is now seen as a versatile hormone that probably has roles both inside and outside the brain. This week, scientists report that leptin may govern mechanisms that prevent cells from storing fat. As a result, the hormone may offer protection against some forms of diabetes.

The new findings emerged from studies of rats with unusually high concentrations of leptin in their blood, explains Roger H. Unger of the University of Texas Southwestern Medical Center in Dallas. To create the animals, he and his colleagues added the human leptin gene to rats.

Like other scientists, Unger's team noticed that almost all fat disappeared from the animals. The slimming was so dramatic that the group suspected more than appetite suppression was involved.

Following up on that suspicion, Unger and his colleagues found that cellular concentrations of triglycerides, commonly known as fat, are significantly lower in rats with extra leptin than in normal rats. Most cells synthesize triglycerides for long-term energy storage.

The researchers then conducted test tube studies in which they exposed rat pancreatic beta islet cells to leptin. …

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