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Tuesday, January 09, 2007

Leptin: The Weight-Loss Hormone

Despite day-to-day variations in food intake and physical activity, a healthy individual maintains a constant body weight and energy reserves of fat over long periods. Clearly, long-term negative feedback mechanisms are at work, but until recently scientists did not understand them. With the discovery of the hormone Leptin ( from the Greek word leptos, meaning thin), researchers have been able to piece together one long adypocytes, the cells in adipose tissue. Fat storage that occurs when food intake exceeds the body's demands stimulates adipocytes to release more leptin into the bloodstream. Centers in the hypotalamus respond to the increased leptin by decreasing food intake and increasing food intake and increasing energy expenditure, which result in weight loss. If this feedback mechanism is disrupted, obesity wil result. For example, mice with a genetic mutation that prevents them from making leptin are obese. Injecting the mice with leptin causes them to lose weight.
After discovering leptin and demonstrating that it could reverse obesity in genetically obese mice, researchers hoped that leptin cold be used to treat obesity in humans. It is now known that unlike genetically obese mice, the vast majority of obese humans are able to make leptib. Human obesity appears to be caused by an inability of the hypotalamus to respond to leptin, rather than our inability to make the hormone.


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