If you regularly read this blog, you may know that the research questions that physiologists ask relate to wide range of topics—cells, tissues and organs, insects and animals, and how the environment influences all of these things. Nowhere is this more apparent than at the annual Experimental Biology meeting. This year, thousands of physiology-based research abstracts were presented over five days. Read on to learn about two research studies on extreme sports that caught our eye.
Credit: Ram Barkai
Ice swimming is growing in popularity, with hundreds of athletes worldwide giving this chilly sport a try. Human performance in water this cold—swims must take place in water that’s 5 degrees Celsius or colder—has not been well-studied. In a study presented at the EB meeting, researchers looked at how age, gender and environmental factors such as wind chill affected athletes during one-mile ice swims. Among other results, they found that age doesn’t have a large effect on swim times, suggesting that athletes can be competitive in the sport well into their 30s and 40s. This is significantly older than the average age of the athletes on the most recent U.S. Winter Olympic team (26 years old), giving hope to older athletes as the sport is being considered as a new Winter Olympics event.
Fifty kilometer (~31 mile) mountain ultramarathons test athletes aerobic and anaerobic fitness through changes in elevation, terrain and weather. Aerobic fitness refers to how the body uses energy when there is enough oxygen, such as the energy burn that occurs when running at a comfortable pace. Anaerobic fitness refers to the body’s ability to exercise when there’s not enough oxygen, such as during a sprint to the finish line at the end of a race. While it may seem that aerobic fitness would be a better predictor of how fast a person would finish an ultramarathon, researchers found that competitors with the best anaerobic fitness finished faster. That’s why exercises that build anaerobic endurance, such as uphill sprints, would be a worthwhile addition to the training regimen of anyone preparing for this type of race.
These studies were just the tip of the iceberg. Read more physiology research highlights from the EB meeting:
How exercise to protect the blood vessels from stress
Why a high-salt and high-sugar diet is a fast track to high blood pressure
The benefits of gastric bypass surgery that occur before the weight comes off
Elephant seals that protect themselves with CO2
What tobacco hornworms can tell us about fat metabolism
How an inhaler could protect against life-threatening accumulation of fluid in the lungs
Credit: Getty Images
Much of what we know about human health and disease comes from studies in male animals. However, researchers are finding that for blood pressure control, what’s true for male animals is not necessarily true for females. One in three adults in the U.S. has high blood pressure (hypertension) and of those, only half have their hypertension under control, according to the Centers for Disease Control and Prevention. Understanding sex differences in the way the disease develops and behaves is important to improve hypertension care for both men and women.
Here are some of the newest findings on hypertension-related sex differences, presented in November at the American Physiological Society’s Physiology and Gender conference:
Women’s kidneys maintain the body’s salt levels differently than men’s. The kidneys are very important organs in the control of blood pressure. They do this by managing levels of sodium (salt) and potassium. Luciana Veiras, PhD, of the University of Southern California showed that female rats that were put on a fast and then fed a diet high in potassium had higher levels of sodium in their urine than their male counterparts did. This demonstrates that female and male kidneys respond differently to increases in blood potassium and suggests that blood pressure control also differs between men and women.
Different hormones may drive obesity-related high blood pressure in men and women. Research has shown that obesity causes hypertension. Fat cells create a hormone called leptin that stimulates the brain to increase blood pressure. However, the reason it increases blood pressure has primarily been studied only in male animals. It was unknown if the same was true for obese female animals. Eric Belin de Chantemele, PhD, of Georgia Regents University, presented findings suggesting that another hormone contributed to obesity-induced high blood pressure in females: aldosterone.
The immune cells that cause hypertension in men may not be the same in women. Studies in male research animals show that inflammation-promoting immune cells are involved in the development of high blood pressure. Jennifer Sullivan, PhD, of Georgia Regents University, presented work suggesting that the immune system actions in cardiovascular disease are not the same in men and women. She found that hypertensive female rats have more anti-inflammatory immune cells. Additionally, the immune cells that cause high blood pressure in male animals aren’t as common in female animals with high blood pressure.
As research studies continue to include more gender diversity, science will uncover more ways that men and women differ in health and disease, making personalized medicine and therapies better for both male and female patients.
Jessica Faulkner, PhD, is a postdoctoral fellow at Augusta University.
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One in three adults in the U.S. has high blood pressure (hypertension). Although men and women are just as likely to develop hypertension during their lifetimes, men younger than 45 have hypertension more often than women that age do. Scientists wondered if this difference is because the male hormone testosterone affects physiological processes differently than the female hormone estrogen does. In the case of hypertension, the suspicion was correct, but it wasn’t the entire story. Recent studies have shown that the gene that gives men the physiological traits to produce testosterone—the SRY gene—may influence blood pressure, too.
Called the sex-determining region of the Y chromosome, SRY is found only on the Y chromosome and carries out its main job after conception when the embryo is developing. SRY turns on the genes involved in the development of male sex organs, triggering the testes to develop and produce the male hormone testosterone. Females don’t have a Y chromosome, nor the SRY gene. Instead, they develop ovaries and produce the female hormone estrogen.
SRY is part of a family of genes whose job is to turn other genes on or off. It is directly related to another gene found on the X chromosome, SOX3. Men have both SRY and SOX3, while women only have SOX3. However, because SRY and SOX3 are from the same family, they control the same genes. In a new study in Physiological Genomics, researchers wanted to know if SRY and SOX3 controlled the genes involved in blood pressure regulation in the same way: Did both of them turn on the genes or did one turn off and the other turn on the genes?
The researchers found that SRY and SOX3 had the same effects on several blood pressure genes except for one gene that produced renin, a protein that raises blood pressure. SRY turned renin production on, while SOX3 turned it off. SRY’s protein was also found in male rats’ kidneys, where renin is made, while SOX3’s was not. This led researchers to believe that renin is only controlled by SRY in males and that blood pressure is controlled differently in men, offering an explanation for why hypertension risks are different between the sexes.
Eat less salt. It’s advice often recommended as a way to reduce blood pressure, but why? And if the body needs sodium (salt) to work properly, how does eating too much of it become unhealthy? In the cardiovascular system, excess sodium changes the body’s physiological processes to encourage high blood pressure, or hypertension. Sodium affects blood volume and the way two key organs—the kidneys and the heart—do their jobs.
Blood is made up of blood cells suspended in plasma—water containing proteins, nutrients, dissolved minerals and cellular waste. The kidneys purify blood by moving the water and everything in it, besides the proteins, out of the bloodstream into its ducts. The nutrients and minerals the body uses, including sodium, are then moved back into the bloodstream. Water is attracted to salt, so it follows sodium back into the bloodstream. The extra minerals and water left behind are filtered out, joined with waste products and excreted as urine.
Eating salt raises the sodium level in the plasma. As a result, more water gets reabsorbed into the blood and the total volume of the blood increases. The heart senses blood volume through how much its chambers are filled. When more blood is present, the heart contracts with greater force and pumps more blood out to the body. This increase in output causes blood pressure to rise.
The kidneys are eventually able to filter out excess sodium into the urine. However, constantly eating a lot of sodium maintains the elevated plasma sodium concentration, slowing down the return to normal blood volume levels and keeping already high blood pressure high.
Limiting dietary salt breaks this cycle. Blood volume decreases, the heart does not pump as strongly and blood pressure falls towards a healthy range. This is why “eat less salt” is heart-healthy advice to remember during American Heart Month and beyond.
– Maggie Kuo, PhD
Reviewed by Barbara E. Goodman, PhD
Correction (3/16/15): An earlier version had said “The kidneys purify blood by moving plasma and everything in it out of the bloodstream into its duct.” Protein actually remains in the blood vessels and do not filter into the kidneys’ ducts. The text has been edited accordingly.