A hormone released by muscles during exercise can be used to prevent complications from surgery, research in mice suggests. Surgical procedures often need to restrict blood flow to organs to make them easier to operate on. But this can cause long-lasting organ damage because it cuts off oxygen and nutrients. One way to limit this damage is to place a blood pressure cuff around the patients arm before the operation and repeatedly squeeze and release it. Cutting off blood supply to the periphery of the body seems to train it to cope better when the same is done during surgery to the central organs, although the reasons for this have been unclear until now. Chunyu Zeng at the Third Military Medical University in China and his colleagues have found that this preconditioning process works by stimulating muscles to release a hormone called irisin. This hormone seems to counteract oxidative stress caused by low blood flow, travelling in the blood to areas of need. Zengs team found that irisin levels tripled in the bloodstreams of mice when their thigh circulation was temporarily cut off. This reduced damage to their lungs when they subsequently underwent surgery that disrupted their lungs blood supply. The same effect was also achieved simply by injecting irisin intravenously before surgery it reduced cell death, inflammation and swelling in lungs when their blood supply was restricted, and improved the survival rates of the mice from 0 to 50 per cent.
Microscope studies revealed that the hormone prevented tissue damage by blocking the release of harmful reactive oxygen species and by preserving mitochondria the energy factories inside cells. Zeng believes that irisin could one day be administered before operations to limit damage to vital organs like the lungs, heart and kidneys. Injections may work better than the blood pressure cuff method because they can achieve higher irisin levels, but this will need to be verified by clinical trials, he says. Jianjie Ma at Ohio State University in the US, who worked with Zeng on the experiments, believes irisin injections might also potentially be used to improve exercise performance. Research has already found that squeezing and releasing blood pressure cuffs on the thighs before cycling improves power output, possibly because it stimulates irisin release. Irisin was discovered relatively recently, in 2012. Since then, researchers have found that it is released by muscles during exercise, and plays a role in many of the health benefits of physical activity including faster metabolism, lower blood pressure, and reduced diabetes risk. However, we still dont know why muscles release irisin during exercise, Ma says.
New Scientist, 29 November 2017 ; http://www.newscientist.com/