Researchers at the University of California, Berkeley, found that oxytocin is indispensable for healthy muscle maintenance and repair, and that in mice, it declines with age.
The findings present oxytocin as the latest treatment target for age-related muscle wasting, or sarcopenia, researchers said.
A few other biochemical factors in blood have been connected to ageing and disease in recent years, but oxytocin is the first anti-ageing molecule identified that is approved by the US Food and Drug Administration for clinical use in humans, the researchers said.
"Unfortunately, most of the molecules discovered so far to boost tissue regeneration are also associated with cancer, limiting their potential as treatments for humans," said study principal investigator Irina Conboy, associate professor of bioengineering.
"Our quest is to find a molecule that not only rejuvenates old muscle and other tissue, but that can do so sustainably long-term without increasing the risk of cancer," she said.
Conboy and her research team said that oxytocin, secreted into the blood by the brain's pituitary gland, is a good candidate because it is a broad range hormone that reaches every organ, and it is not known to be associated with tumours or to interfere with the immune system.
The researchers pointed out that while oxytocin is found in both young boys and girls, it is not yet known when levels of the hormone start to decline in humans, and what levels are necessary for maintaining healthy tissues.
The new study determined that in mice, blood levels of oxytocin declined with age. They also showed that there are fewer receptors for oxytocin in muscle stem cells in old versus young mice.
To tease out oxytocin's role in muscle repair, the researchers injected the hormone under the skin of old mice for four days, and then for five days more after the muscles were injured.
After the nine-day treatment, they found that the muscles of the mice that had received oxytocin injections healed far better than those of a control group of mice without oxytocin.
"The action of oxytocin was fast. The repair of muscle in the old mice was at about 80 per cent of what we saw in the young mice," said Christian Elabd, senior scientist in Conboy's lab, and co-lead author on the study.
Giving young mice an extra boost of oxytocin did not seem to cause a significant change in muscle regeneration.
The researchers also found that blocking the effects of oxytocin in young mice rapidly compromised their ability to repair muscle, which resembled old tissue after an injury.
The study was published in the journal Nature Communications.