Insulin Receptors Influence Hunger
October 01, 2000
Insulin receptors in the brains of mice are involved in appetite,
weight gain and fertility, new research has shown.
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.
Insulin is a key hormone in metabolism,
and its levels rise as levels of body fat rise.
Although obese people often have chronically high insulin levels,
they often become or are already resistant to the hormone and eventually
While it is well known that tissue such as muscle and fat can become
insulin resistant, it had been assumed previously that the brain
is not sensitive to insulin.
This study, however, confirms earlier evidence that insulin receptors
in the brain help control food intake and body weight.
The fact that knocking out the brain's insulin receptors triggered
infertility in the mice was something of a surprise finding to many.
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, as noted in another article this week.
One researcher proposed that it is possible
that insulin resistance and leptin resistance act together in the
onset of obesity and diabetes.
Science September 22, 2000;289:2122-2125.