A kind of bone hormone helps human escape

Adrenaline is a synonym for anything that makes our blood boil - whether it's meeting a rattlesnake or watching the latest horror movie But a new study suggests that when our bodies respond to stress, adrenaline may not be as important as another hormone, a substance that seeps out of our bones Gerard Karsenty, a geneticist at Columbia University, said: 'our bones are not just a rigid scaffold for our bodies Human bones can secrete a protein called osteocalcin, which was discovered in the 1970s and can reconstruct bones In 2007, Karsenty and his colleagues found that the protein, as a hormone, controls blood sugar levels and burns fat Later, his team proved that the hormone is essential for maintaining brain function and physical health, restoring memory in old mice, and improving the performance of old mice and humans in sports These findings led Karsenty to assume that animals evolved skeletons to avoid danger This new study further supports this view Karsenty and his colleagues exposed mice to several stress factors, including a mild foot shock and a stink of fox urine, an odor that triggers a natural fear response The researchers then measured the blood osteocalcin levels of rodents The results showed that the level of osteocalcin in mice increased fourfold within two to three minutes of exposure to a stress source A typical stress factor has a similar effect on people - when researchers asked volunteers to speak in front of some audience, their osteocalcin levels soared The team reported the findings in the September 12 issue of cell metabolism Next, Karsenty's team began to determine whether osteocalcin was necessary to trigger a pattern of fight or flight, or whether it was an unconscious physiological response to a threat This pattern includes a faster heart rate, more breathing, and higher blood sugar; the response provides the body with extra energy to prepare for a quick escape When the team exposed genetically engineered mice that did not produce osteocalcin to the same stress factors as non genetically engineered mice, there was little response In normal mice, a single dose of osteocalcin was enough to trigger a flight or fight response, even without a single stressor By studying the neural connections between rodent brains and their bones, the team found how osteocalcin triggers fight or flight patterns The researchers found that when danger was detected in an area of the brain called the amygdala, it indicated that osteoblasts released osteocalcin into the blood Osteocalcin, in turn, inhibits the activity of the parasympathetic nervous system, a nerve fiber that slows heart rate and respiration Karsenty said this eventually causes the sympathetic nervous system to stop working and release the body's stress response, including the release of adrenaline Karsenty says the results show that osteocalcin, not adrenaline, is the gatekeeper who determines when the body enters combat or escape mode The findings also help explain why rodents that have had their adrenals removed, and those who are not able to produce too much adrenaline for health reasons, are still able to have a strong physiological response to risk Patricia buckendahl, a bone physiologist at Rutgers University in New Brunswick, N.J., who was not involved in the study, said the study was "absolutely newsworthy" and supported the hypothesis that bone evolution was designed to help animals escape predators and other threats Buckendahl presented the first evidence of osteocalcin as a stress hormone in rats 20 years ago, but no one took this idea seriously at that time "I always thought bones weren't just a place to store calcium," she said