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When an animal faces a predator or a sudden danger, the heart rate increases, breathing becomes faster and fuel in the form of glucose is pumped throughout the body to prepare the animal to fight or to flee.
It is thought that these physiological changes, which constitute the "fight or flight" response, are caused in part by the release of the hormone adrenaline.
But a new study by researchers in Colombia suggests that bone vertebrates can not muster this response to danger without the skeleton. The researchers found in mice and humans that, almost immediately after the brain had identified a danger, it ordered the skeleton to ingest the blood with osteocalcin, a hormone of bone origin, necessary to trigger the fight or flight response.
"In bone vertebrates, the response to acute stress is not possible without osteocalcin," says Gerard Karsenty, principal investigator of the study, director of the Department of Genetics and Development at Columbia University's College of Physicians and Surgeons. Vagelos.
"It completely changes the way we think about how responses to acute stress occur."
Why bones?
"Bone vision as a simple assembly of calcified tubes is deeply rooted in our biomedical culture," says Karsenty. But about a decade ago, his lab hypothesized and demonstrated that the skeleton had hidden influences on other organs.
Research has revealed that the skeleton releases osteocalcin, which travels through the blood to affect the functions of the biology of the pancreas, brain, muscles, and other organs.
A series of studies conducted since then has shown that osteocalcin helps regulate metabolism by increasing the cells' ability to absorb glucose, improves memory, and helps animals run faster with greater endurance. .
Why do bones all have these seemingly unrelated effects on other organs?
"If you think the bone has evolved to protect the body from danger – the skull protects the brain from trauma, the skeleton allows vertebrates to escape predators, and even the bones of the body." 39 ear advise us of imminent danger – the hormonal functions of osteocalcin begin to make sense, "says Karsenty.If the bone evolved to escape danger, Karsenty hypothesized that the Skeleton should also be involved in the response to acute stress, which is activated in the presence of danger.
Osteocalcin needed to react to danger
If osteocalcin contributes to the response to acute stress, it must act quickly within the first few minutes after the hazard is detected.
In the new study, researchers presented mice with predator urine and other stressors and looked for changes in the bloodstream. In less than two or three minutes, they saw their osteocalcin levels increase.
Similarly, the researchers found that osteocalcin also increased in people under stress from public speaking or cross-examination.
As osteocalcin levels increased, heart rate, body temperature, and blood glucose levels in mice also increased as the response to combat or flight became effective.
In contrast, genetically modified mice, unable to manufacture osteocalcin or its receptor, were totally indifferent to the stressor. Said Karsenty. "Without osteocalcin, they did not react strongly to the perceived danger," says Karsenty. "In the wild, they would have a short day."
In the final test, the researchers were able to elicit an acute stress response in unstressed mice, simply by injecting large amounts of osteocalcin.
Adrenaline is not necessary for fight or flight
The results could also explain why animals without adrenal glands and insufficient adrenal patients – with no way to produce adrenaline or other adrenal hormones – can develop an acute stress response.
In mice, this ability disappeared when the mice were unable to produce large amounts of osteocalcin.
"This shows us that circulating levels of osteocalcin are enough to stimulate the response to acute stress," says Karsenty.
Physiology: new frontier of biology
Physiology may seem to be an old-fashioned biology, but new genetic techniques developed over the past 15 years have established it as a new frontier of science.
The ability to inactivate unique genes in specific cells within an animal and at specific times has led to the identification of many new inter-organ relationships. The skeleton is only one example. the heart and muscles also exert an influence on the other organs.
"I have no doubt that there are many more new inter-organ signals to discover," says Karsenty, "and these interactions can be as important as those discovered in the early twentieth century."
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