Insulin, the hormone long linked to metabolism and metabolic disorders such as diabetes, is directly linked to core body temperature, scientists have discovered.
This is the first time the hormone has been associated with the fundamental process of temperature regulation.
A team led by scientists at The Scripps Research Institute found that when insulin was injected directly into a specific area of the brain in rodents, core body temperature rose, metabolism increased, and brown adipose (fat) tissue was activated to release heat.
The research team also found that these effects were dose-dependent-up to a point, the more insulin, the more these metabolic measures rose.
"Scientists have known for many years that insulin is involved in glucose regulation in tissues outside the brain. The connection to temperature regulation in the brain is new," said Scripps Research neurobiologist Manuel Sanchez-Alavez, who was first author of the new paper with Bartfai lab colleagues Iustin V. Tabarean and Olivia Osborn (now at the University of California, San Diego).
In addition to suggesting a fresh perspective on diseases such as diabetes that involve the disruption of insulin pathways, the study adds to the understanding of core body temperature-the temperature of those parts of the body containing vital organs, namely the trunk and the head.
Normally, core body temperature stays within a narrow range so that key enzymatic reactions can occur. When core body temperature goes outside this range for prolonged periods-higher as in fever, or lower as in hypothermia-the result is harm to the body.
More modest variations in core body temperature are associated with the daily 24-hour sleep-wake cycle, the female monthly hormonal cycle, and, intriguingly, the effects of severe calorie restriction.
Osborn said: "Our paper highlights the possibility that differences in core temperature may play a role in obesity and may represent a therapeutic area in future drug design."
The study was published recently in an advance, online issue of the journal Diabetes.