Orexin is a hormone in the brain named after its role in the appetite. The word is derived from the Greek term for "appetite." There are two types of orexin found in the brain, known as orexin-A and orexin-B; these compounds may also be referred to as hypocretins. Researchers are studying the role of these hormones in the body to learn more about them and to determine whether or not they have potential clinical and medical applications.
Researchers first began to identify these hormones in the 1990s, starting with finding the gene involved in their production in the brains of rats. Over time, they were able to find the hormone itself, along with receptors in the brain that are sensitized to it. This laid the groundwork for research that could be used to learn more about how it functions, how the body regulates production of the hormone, and what is involved in metabolizing this hormone to clear it from the body when it is no longer needed.
One key role of orexin in the brain involves the regulation of appetite. This hormone also determines wakefulness levels. Studies with monkeys showed that animals deprived of sleep and exposed to orexin could perform much like monkeys that had been well rested, establishing the possibility of using the drug to treat sleep disorders and as a supplement for people who do not sleep enough.
Other studies with rats have demonstrated that those with more orexin receptors in their brains tend to be slimmer. This suggests that the hormone also plays a role not just in regulating appetite, but in regulating weight and overall metabolism. It does so in conjunction with other hormones as part of a complex system that keeps the body functioning; thus, orexin should not be viewed as a potential quick fix for people who are attempting to lose weight and keep it off.
Like other hormones, orexin is chemically complex, and because it works in concert with other hormones, it can be difficult to tease out its precise functions and to study the way it interacts with other hormones in the body. Extensive research can provide scientists with tools for understanding which hormones orexin interacts with and how. This in turn can be used to learn more about what this hormone does in the body and how it could potentially be synthesized and used to treat specific medical issues such as narcolepsy and sleep deprivation.