The body knows how to be young. It had no trouble being young X years ago. Now the body is choosing to be old, slowing down its repair and re-building functions, gradually destroying itself with inflammation, eliminating nerve and muscle cells via apoptosis. In doing this, the body is following hormonal signals that circulate in the blood. If the hormonal signals say, “old”, then the body is old; and if the hormonal signals say “young”, then the body will respond appropriately.
This is my premise about what aging is, how it works, and how it can be addressed medically. (Not everyone thinks this way ─ but you already know that.) I call it the “epigenetic theory of aging”, and I’ve blogged about it here and written more technicallyhere. Last summer, I listed some of the hormones that we don’t have enough of in old age, and some that we have too much of.
Oxytocin is a Stem Cell Signal
Oxytocin levels decline with age, and this summer, there was an article in Naturesuggesting that it may be one of those signals that help to keep us young. Aging mice with extra oxytocin retained muscle mass that was lost by mice of similar age as their oxytocin naturally declined. Oxytocin signals the muscle stem cells (aka satellite cells) to actively divide and make more muscle cells. The study’s authors note, however, that the satellite cell receptor for oxytocin also declines with age, so that the problem of muscle loss is really compounded, and may need to be addressed at both ends.
The reduction in muscle mass in humans starts in the third decade of life and accelerates after the fifth decade, resulting in a decrease in strength and agility. Muscle ageing is characterized by a deficiency in muscle regeneration after injury and by muscle atrophy associated with altered muscle function, defined as sarcopenia. The limiting step in muscle regeneration after injury is the activation of the muscle stem cells, or satellite cells…Satellite cells from old muscle are intrinsically able to repair damaged muscle, but are reversibly inhibited by the aged niche, yet can be quickly rescued for productive tissue repair by a number of experimental methods, including heterochronic parabiosis. While the rejuvenating effects of heterochronic parabiosis have been observed in several tissues such as muscle, brain, liver, pancreas and heart the molecular mechanisms are not fully understood and…to date, few circulating molecules decreasing with age have been identified to be responsible for skeletal muscle ageing.
Other roles of oxytocin
Oxytocin is known for several other functions. It suppresses our fear and protectiveness. Delivered intraveinously to women in labor (as Pitocin) it helps to strengthen contractions. It is also thought to be related to bonding between parent and child, between lover and lover. In popular literature, it is referred to as “the love hormone”, with some justification. But it doesn’t necessarily make us feel good or improve our judgment; rather it shifts our feelings in the direction of more trusting, less self-protectiveness, more caring, with results that can be good or bad depending on circumstances.
Oxytocin is released in the body in response to physical touching and especially during sexual orgasm. Massage often triggers oxytocin.
What is “heterochronic parabiosis”?
The research comes from the lab of Irina and Mike Conboy, who have pioneered work in “heterochronic parabiosis”. This is an experimental setup in which an old mouse and a young mouse are joined surgically, like Siamese twins. It has been noted that the admixture of young blood promotes wound healing and nerve growth in the older mouse. This raises the promise of a possible path toward rejuvenation, but the experimental technique must be refined in order to answer the obvious questions
- Can the old mouse be rejuvenated in general, systemic ways?
- Is its life expectancy affected by addition of young blood?
- What are the blood factors reponsible for the effect?
The Conboys are already well into the next phase,
- designing ways to infuse blood into a mouse without the trauma of Siamese surgery, and
- separating different hormones in the blood so they can be tested individually and in combination.
They and other researchers have concluded that it is not the red blood cells or the white blood cells, but rather the blood plasma that carries the benefit. Blood plasma contains many dissolved hormones, sourced from all the body’s internal secretion organs. Some are up-regulated with age, and some are down-regulated. The hypothesis is that there is not one magic hormone that makes us young, but rather it is the quantitative balance of various hormones that signals the age state of the body.
You heard it first on the Aging Matters blog
I’m going to go out on a limb and suggest a theoretical hypothesis that might help to inspire and direct future research: It is well-established that social connectivity is a predictor of longevity in humans. But the mechanism is unknown by which social factors affect individual life span. Perhaps oxytocin plays an intermediary role, signaling the body in response to social connection, and promoting longevity.
There is a whole branch of aging literature relating social factors to aging and mortality. People who are more connected have lower death rates. Sexual activity, too, has been linked to longevity, especially in men. Married women and especially men have lower mortality rates than un-married or divorced people. People with regular volunteer activities have lower mortality rates than people who devote all their energy to pleasing themselves, after adjusting for health and mobility factors. More money is associated with longer life, and independently, careers with more responsibility lend to longevity [British Whitehall Study].
In all these areas, it is especially difficult to disentangle cause from effect. You can’t very well randomly assign people to two groups and ask the first group to make passionate love with a standardized partner twice a week, while the second group gets equivalent exercise from walking. Even more difficult would be to conceal from the experimental subjects (until the experiment was over) to which group they had been assigned.
In this context, understanding biochemical mediators can help to guide research and design experiments. We should be working toward an integrated view of human health that looks upon chemistry and behavior as two lenses for viewing one underlying reality.
Oxytocin’s uses, present and future
Here is Dr Sahelian’s page on oxytocin.
Oxytocin has long been available as an intravenous medication used for women in labor. More recently, there is a nasal spray that is finding intriguing applications for autism. Experimental use of oxytocin for enhanced intimacy or sexual experience has had mixed results. Whether it can find a role in longevity treatment is something we should know within a few years.
We look forward to the day when we can self-administer convenient doses of oxytocin and maybe enhance oxy-receptors as well. Until then, I guess we’ll just have to make do with massages and orgasms.
This article originally appeared in Josh’s blog here: http://joshmitteldorf.scienceblog.com/2014/08/09/love-death-and-oxytocin/