Bone may play more critical role in fight or flight response than adrenal gland

Many are familiar with the fight or flight response--heart rate goes up, blood is routed to muscle, airways and pupils dilate and so on. The sympathetic branch of the autonomic nervous system is needed to trigger this response. I teach physiology, and all the textbooks state that stimulation of the adrenal medulla by the SyNS triggers the release of a hormone called epinephrine (more popularly known as adrenaline), which is essential for initiating these responses in vertebrates. Indeed, the knowledge of adrenaline is so ubiquitous in pop culture that writers describe that "fight or flight" feeling as "the adrenaline coursing through a character's veins." Even when the novel is set in a time and place where no one knew about endocrinology at all (a point of view violation that is something of a writerly pet peeve of mine, but that's another issue).

Well, it appears that adrenaline needs to move over. A bone-derived hormone appears to be needed to initiate this response.

But a new study from Columbia researchers suggests that bony vertebrates can't muster this response to danger without the skeleton. The researchers found in mice and humans that almost immediately after the brain recognizes danger, it instructs the skeleton to flood the bloodstream with the bone-derived hormone osteocalcin, which is needed to turn on the fight or flight response.

"In bony vertebrates, the acute stress response is not possible without osteocalcin," says the study's senior investigator Gérard Karsenty, MD, Ph.D., chair of the Department of Genetics and Development at Columbia University Vagelos College of Physicians and Surgeons.

"It completely changes how we think about how acute stress responses occur."

"The view of bones as merely an assembly of calcified tubes is deeply entrenched in our biomedical culture," Karsenty says. But about a decade ago, his lab hypothesized and demonstrated that the skeleton has hidden influences on other organs.

The research revealed that the skeleton releases osteocalcin, which travels through the bloodstream to affect the functions of the biology of the pancreas, the brain, muscles, and other organs.

A series of studies since then have shown that osteocalcin helps regulate metabolism by increasing the ability of cells to take in glucose, improves memory, and helps animals run faster with greater endurance.

Click to expand...

https://phys.org/news/2019-09-bone-...YTQH6RgfiotCp8a1BAo5D08EfSgSJqr_JreoKigm1hH7w

We already knew, of course, that bone is a dynamic and physiological tissue and is more than a simple internal scaffolding for our bodies.

One caveat is that it is possible mice aren't typical of vertebrates in general, but there is no reason why they should be different in this particular element of their physiology when they aren't outliers in others. And it does explain a longstanding mystery: why people with adrenal insufficiency can still still initiate an acute fight or flight response.

Yet another hormone to add to the endocrine system chapter.