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Muscles Love Oxytocin: So-Called "Hug Hormone" Important In Muscle Regeneration

Science Sushi
By Christie Wilcox
Jun 28, 2014 6:34 AMNov 20, 2019 5:16 AM


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The 'love drug'? More like the muscle rejuvenator! I've written before about the most lovable molecule on the planet, oxytocin, and how it isn't the warm and fuzzy chemical it's purported to be. Though you'll often hear it referred to as the 'love hormone' or the 'trust molecule', oxytocin has a wide variety of effects in our bodies. For the most part, though, scientists (and especially the media) have focused on how it affects our behavior—how sniffing oxytocin changes how so-and-so group of people act when doing such-and-such. But this month, scientists from University of California Berkley reported on a completely different effect of oxytocin—one that has nothing to do with love, trust, or how we behave—and it's one that might just make the most overhyped molecule on the planet deserve a little bit of the love it gets. Oxytocin is made in our brain's hypothalamus, but receptors for the hormone can be found in tissues all over the body. There has been some investigation into oxytocin's bodily effects—previous studies have found that oxytocin is important in regulating lactation and giving birth, for example—but the bulk of oxytocin research has focused on how it affects our minds. Recently, scientists have begun to investigate how oxytocin affects the body as a whole, noting that a lack of it leads to obesity while an abundance of it helps fight against osteoperosis and ischemic injury during a heart attack. All of these results suggest that oxytocin plays an important role outside our brains—but the pathway by which oxytocin has these effects has thus far remained shrouded in mystery. The UC Berkley team decided to test the effects of oxytocin using animal models. They first investigated how oxytocin levels change with age, and discovered that oxytocin levels drop in older mice. Similarly, the expression of oxytocin receptors in muscle satellite cells was markedly lower in older animals, suggesting that oxytocin might act as an hormonal indicator of youth. Which made the team wonder: could oxytocin help reverse age-related problems? As we get older, our bodies stop working as well as they once did. Our bodies become weaker and more frail because our innate systems of tissue regeneration begin to slow or fail. Our bones, for example, become less dense—a condition known as osteopenia—which can lead to osteoperosis. But our bones aren't the only body parts that degrade with age. Our muscles, too, become weaker because our bodies are unable to regenerate muscle fibers at the same rate. Previous studies have found that there's something in young blood that stimulates our bones and muscles to grow, but so far, isolating exactly which factors contribute to growth stimulation has been difficult. So when the UC team saw that oxytocin levels in the blood decreased with age, it piqued their interest. Maybe, they thought, oxytocin helps reverse the effects of aging on our bodies. To test their hypothesis, the team injured muscles in young and old mice, then injected some of the muscles with oxytocin. Overall, the muscles in the young mice regenerated faster than the muscles in the older ones, as we would expect. But when the older mice were given an oxytocin boost, their muscles regenerated faster, bringing their regeneration rate up to the speed of youth. The young mice, on the other hand, received no added benefit from an extra shot of oxytocin, but their muscle regeneration was dramatically hampered when injected with an oxytocin receptor inhibitor. When the team looked closely at what was happening in the regenerating muscle cells, they found that oxytocin turns on a well-known cellular cascade that triggers growth and proliferation: the MAPK/ERK signaling pathway. "Our results demonstrate that oxytocin is one of the key age-specific systemic regulators of muscle maintenance and repair," write the authors in their conclusions. However, they're quick to note that it's probably not the only one. "It is unlikely that only one circulating molecule accounts for systemic aging or rejuvenation." Still, any molecule that helps combat the effects of aging is a good find, especially this one—because, so far, negative side effects from oxytocin use are few and far between. What's most exciting about this research is that oxytocin is already an FDA-approved drug, thus this work may have uncovered a novel and safe way to combat the deterioration of muscle mass, strength and agility in the elderly. As the authors explain, "the potent positive effects of oxytocin on muscle tissue homeostasis and repair that were uncovered in this study are thus promising for developing an effective and safe new clinical strategy." Now that's a good reason to <3 the so-called love hormone! Citation:

Elabd C., Cousin W., Upadhyayula P., Chen R.Y., Chooljian M.S., Li J., Kung S., Jiang K.P. & Conboy I.M. (2014). Oxytocin is an age-specific circulating hormone that is necessary for muscle maintenance and regeneration., Nature communications, PMID: http://www.ncbi.nlm.nih.gov/pubmed/24915299

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