Hormone may assist dieters


Published: Thursday, January 29, 2004 at 6:01 a.m.
Last Modified: Wednesday, January 28, 2004 at 10:51 p.m.

Need more motivation to eat better and get more exercise? Here's something to chew on.

A University of Florida study on rats suggests dieters who persevere long enough to lose a few pounds may be rewarded with help from a slimming hormone that's otherwise stifled by excess fat.

The study showed that adult rats fattened on a high-calorie diet returned to their original weights when scientists used gene therapy to produce that hormone, called leptin, in the rodents' brains.

Satya Kalra, a UF College of Medicine professor of neuroscience who led the study, notes that mammals - including people - produce the hormone in their fat cells.

Leptin helps regulate energy use by signaling the brain to reduce appetite and burn more calories, Kalra said.

There is no magic pill - including leptin - for weight loss, but the study could have implications for some of the 59 million Americans now classified as obese by the Centers for Disease Control and Prevention.

However, there's a caloric Catch-22 to the leptin study: Overweight mammals produce more leptin, so much that it impairs the very mechanism that should eliminate excess fat.

"For reasons unknown, when leptin levels are increased in the blood (leptin is) ineffective in performing its normal function - sometimes referred to as leptin resistance," Kalra said. "It increases more quickly if the animal consumes a diet that's very rich in calories."

Although the findings reported in the current issue of Obesity Research suggest leptin could eventually provide better weight-control methods, Kalra said they are primarily a reminder that unwanted pounds are best fought with persistence and prevention.

"The take-home message (of our study) is it's very important that we maintain a healthy lifestyle," said Kalra, a member of UF's McKnight Brain Institute. "That includes a lot of energy expenditure through exercise and tight control on calorie intake."

For several years, Kalra and his wife, Pushpa Kalra, a UF professor of physiology and functional genomics, have sought to overcome leptin resistance in rats and mice by delivering leptin-producing genes to the hypothalamus, an area of the brain that controls many basic body functions and contains receptors activated by leptin. The current study focused on a tiny subdivision of the hypothalamus called the paraventricular nucleus.

"Most of the data (from past studies) indicate that the paraventricular nucleus is one of the most important targets for the action of neurotransmitters that stimulate or inhibit appetite, and also the neural circuits that increase energy expenditure," Satya Kalra said.

Next, UF researchers hope to learn how long the paraventricular nucleus produces leptin after gene therapy is administered, Kalra said.

Because the procedure involves surgery, possible human applications are years away, but the researchers hope that knowledge gained through the rat studies may lead to noninvasive methods of overcoming leptin resistance.

Diane Chun can be reached at (352) 374-5041 or chund@gvillesun.com.

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