Skin, the largest organ, typically covering two square metres in humans, plays a surprising role in regulating blood pressure and heart rate, scientists have found in a study on mice.
When it comes to high blood pressure, a lack of exercise and a poor diet are often the primary suspects. But the new findings revealed that the skin helps regulate hypertension and heart rate in response to changes in the amount of oxygen available in the environment.
By studying mice, researchers from the United Kingdom and Sweden found that the skin responds to levels of oxygen in the environment, which influences blood pressure levels.
High blood pressure, the risk factor for heart attack and stroke, is often caused as a result of the reduced flow of blood through small blood vessels in the skin and other parts of the body to the heart.
''Given that skin is the largest organ in our body, it perhaps shouldn't be too surprising that it plays a role in regulating such a fundamental mechanism as blood pressure,'' said co-author Prof Randall Johnson of the University of Cambridge.
When the heart tissue is starved of oxygen - as can happen in areas of high altitude, or in response to pollution, smoking or obesity - blood flow to that tissue will increase. In such situations, the increase in blood flow is controlled in part by the 'HIF' family of proteins.
For the study, published in the journal eLife, the team exposed genetically modified mice to such low-oxygen conditions. The mice, which lacked in one of two proteins in the skin (HIF-1a or HIF-2a) showed an effect on the heart rate, blood pressure, skin temperature and general levels of activity.
''These findings suggest that our skin's response to low levels of oxygen may have substantial effects on the how the heart pumps blood around the body,'' said first author of the study Prof Andrew Cowburn, senior research associate at the university.
Prior studies have revealed that blood pressure is regulated by the brain, by blood vessels, or by the kidney. However, the study ''suggests that we may need to take a look at other organs and tissues in the body and see how they, too, are implicated'', in controlling blood pressure. Here are High BP can cause organ damage in teenagers too.
Being overweight, not partaking in physical activity, and eating a poor diet are major risk factors for high blood pressure, but according to Prof Johnson and team, many hypertension cases arise with no known cause.
''Most research in this area,'' says Prof. Johnson, ''tends to look at the role played by organs such as the brain, heart and kidneys, and so we know very little about what role other tissue and organs play.''
The study also revealed some interesting findings regarding the body's response to low oxygen in healthy mice. The researchers found that blood pressure and heart rate began to rise in the healthy rodents within 10 minutes of hypoxia, before falling to below normal levels for up to 36 hours.
By 48 hours after exposure to low-oxygen conditions, the blood pressure and heart rate of the healthy rodents returned to normal.
The scientists note that a lack of HIF proteins, as well as other proteins associated with hypoxia, in the skin affected the point at which heart rate and blood pressure started to rise, as well as how long they were increased.
Given that the skin is the body's largest organ, Prof Johnson notes that perhaps its role in blood pressure regulation should not come as a surprise.
''But this suggests to us that we may need to take a look at other organs and tissues in the body and see how they, too, are implicated,'' he concludes.