Fighting obesity: How does orexin get to leptin?
Increased sensitivity to the "satiety hormone" stopped the weight gain of miceOne of the neurohormones of the pituitary gland, orexin, is able to increase the sensitivity of the brain to the "satiety hormone" leptin and thereby help to cope with obesity.
However, orexin will have to be injected into the brain through a hole in the skull: orexin cannot pass into the brain from the blood through the blood-brain barrier.
Scientists from the University of Texas Southwestern Medical Center, led by Masashi Yanagisawa, have shown that mice whose brains are injected with additional amounts of orexin or who are genetically programmed to increase its production do not gain weight even on a fatty diet.
With a normal diet, an excess of orexin did not affect weight gain in any way in comparison with control mice, however, on a fat mouse, ordinary mice gained weight much faster than mice with an excess of orexin in the brain. As the researchers showed, orexin accelerated energy metabolism by about 20% – probably due to increased sensitivity to leptin. The corresponding work (Hiromasa Funato et al., Enhanced Orexin Receptor-2 Signaling Prevents Diet-Induced Obesity and Improves Leptin Sensitivity) is published in Cell Metabolism.
At the same time, the mice did not show violations of the sleep-wake cycle, despite the fact that a lack of orexin leads to narcolepsy among both mice and humans.
Scientists hope that orexin will help to cope with the epidemic of obesity that has engulfed developed countries. Most people who are overweight have more than normal levels of leptin, which signals to the brain about satiety, but for some reason the brain does not respond to it, and continues to feel hungry.
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