|Thursday September 21 5:54 PM ET |
Insulin receptors tied to appetite, weight gain
By Amy Norton
NEW YORK (Reuters Health) - In a study that suggests the brain could be a prime target in treating obesity and type 2 diabetes, researchers have found that insulin receptors in the brains of mice are involved in appetite, weight gain and fertility.
When researchers ``knocked out'' insulin receptors in the brains of genetically altered mice, they discovered that the animals ate more, put on fat, had fertility problems, and developed insulin resistance throughout the body--a precursor to diabetes in humans.
Their findings are published in the September 22nd issue of Science.
Insulin is a key hormone in metabolism, and its levels rise in tandem with body fat. Because obese people have chronically high insulin levels, they often become resistant to the hormone and eventually develop diabetes. While tissue such as muscle and fat are known to become insulin resistant, conventional wisdom has held that the brain is not sensitive to insulin.
The current study, however, confirms earlier evidence that insulin receptors in the brain help control food intake and body weight. Whether insulin resistance in the brain triggers obesity or results from it remains unclear, said Dr. C. Ronald Kahn of the Joslin Diabetes Center and Harvard Medical School (news - web sites) in Boston, Massachusetts.
Research such as this, Kahn told Reuters Health, lays the groundwork for developing new treatments for obesity and diabetes drugs that, for example, improve insulin sensitivity in the brain so that people ``feel more full'' from food.
The fact that knocking out the brain's insulin receptors triggered infertility in the mice was something of a surprise, Kahn said. However, he noted that obesity and diabetes are linked to reproductive problems.
The mice showed increased levels of the ``obesity hormone'' leptin, as well. Leptin is believed to help the body regulate fat, perhaps through triggering feelings of satiety.
Leptin resistance has also been linked to obesity. Kahn said it is possible that insulin resistance and leptin resistance act together in the onset of obesity and diabetes.
SOURCE: Science 2000;289:2122-2125.