Friedman notes the hypothalamus, the part of the brain that coordinates basic bodily functions such as food intake, is likely to receive leptin's signal, either directly or indirectly. Obesity, defined as being more than 20 percent over an ideal weight, is a major risk factor for diabetes, heart disease, high blood pressure, stroke, sleep apnea, gallstonesas well as some cancers and forms of arthritis. In the last 10 years, the number of overweight Americans has increased from 25 to 34 percent. The researchers measured the amounts of leptin in mouse blood and found that mice with a defective ob gene do not make the hormone. The db mice are thought to have a defective leptin receptor.
Receptors are specialized proteins that receive cellular signals.
The investigators also found leptin in the blood of six lean humans. In a four-week mouse study, the investigators gave sets of 10 ob , db and normal mice daily injections of mouse leptin, made in the laboratory by inserting the ob gene into bacteria. Each of the mice received 5 milligrams leptin per kilogram of body weight. For comparison, control mice received either injections of a salt solution or no treatment. After two weeks of treatment with leptin, the ob mice lost 30 percent of their body weight without side effects.