A Hazard of Some Pregnancies Becomes Clearer to Scientists

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The discovery of a relationship between oxygen and a hormone has brought researchers closer to understanding why some pregnant women develop pre-eclampsia, a potentially fatal condition marked by high blood pressure and excess protein in the urine.

Pre-eclampsia occurs when the placenta doesn't form properly during pregnancy, leading to an overabundance of destructive free radicals in the blood, according to the University of Nottingham in Great Britain.

The new study by Fiona Broughton Pipkin and her fellow researchers at Nottingham shows that once the free radicals provoke changes in oxygen levels in the bloodstream, it spurs an increase in levels of the protein that triggers the production of angiotensin. Angiotensin is a blood-pressure-increasing hormone.

Free radical link

"Most pregnant women produce antioxidants that beat off the excess radicals," Broughton Pipkin, who works in the university's Department of Obstetrics and Gynecology, told MyHealthNewsDaily. "But some women, for genetic reasons or other reasons, can't make enough of the mechanisms that beat these free radicals normally."

Researchers from the University of Cambridge previously had found, in a test-tube experiment, that angiotensin responds to changes in blood oxygen levels. Nottingham researchers looked for this effect in humans.

Researchers examined the blood of 12 women with pre-eclampsia and 12 other pregnant women. They found that blood levels of the protein needed to make angiotensin were four times higher in pre-eclamptic women than in healthy women.

"That's a lot, and that could be a factor in the high blood pressure," Broughton Pipkin said. "It isn't fair to say this is the cause, but it is to say this is a very new way of looking at the very early origins of pre-eclampsia."

The researchers linked the elevated levels of this protein to a higher number of free radicals in the blood.

Pre-eclampsia, which occurs in 6 percent to 8 percent of pregnancies, is the leading cause of fetal complications, according to the National Heart Lung and Blood Institute, one of the U.S. National Institutes of Health. Chronic hypertension, diabetes, kidney disease or obesity presents a high risk for the condition. Pregnant women younger than 20 or older than 40 also are at high risk.

Women at risk of developing pre-eclampsia should eat a lot of fruits and vegetables with high levels of antioxidants, which fight free radicals in the blood, Broughton Pipkin said.

Next, she hopes to look at tissue samples from women who have had repeated miscarriages, because those women also become at high risk for pre-eclampsia. Research into the mechanisms behind increased blood pressure brings scientists closer to a treatment for the condition, Broughton Pipkin said.

Not just in pregnant women

The oxygen-hormone link could be a factor in high blood pressure in people besides pregnant women, though more research is needed before that association can be made, she said.

Currently, millions of people with high blood pressure take drugs called angiotensin-converting enzyme inhibitors, or ACE inhibitors, to block the production or action of angiotensin.

The study was published today (Oct. 6) in the journal Nature.

Amanda Chan
Amanda Chan was a staff writer for Live Science Health. She holds a bachelor's degree in journalism and mass communication from the Walter Cronkite School of Journalism and Mass Communication at Arizona State University, and a master's degree in journalism from Columbia University.