Preeclampsia Tied to Lack of Nitric Oxide
Finding implicates vitamin C deficiency
THURSDAY, June 7, 2001 (HealthDayNews) -- A deadly pregnancy condition that clamps a woman's blood vessels appears to be linked to a dearth of a gas that keeps the vessels relaxed, a new study says.
Compared with normal women, pregnant women with preeclampsia have significantly higher concentrations of blood markers that reflect abnormal hoarding of nitric oxide, which is vital to vessel health. Nitric oxide is released by cells lining the walls of vessels, relaxing the tissue and lowering blood pressure.
Preeclampsia is a blood pressure abnormality that causes 75,000 maternal deaths each year worldwide. It is a leading reason for premature deliveries to save the lives of the mothers. The problem for a mother ends after the baby is born.
The hike in blood pressure results from a clamping of the vessels throughout the body, threatening a woman's organs.
Although scientists aren't sure what causes preeclampsia, which affects about 5 percent of pregnancies in this country, obese women and those in their first pregnancy are more prone to the disorder. In developing countries, poor nutrition may play a role. Studies also have pointed to a genetic factor in the condition.
Researchers have known for some time that women with preeclampsia have about half as much ascorbate, or vitamin C, in their blood as healthy mothers. Vitamin C is a key player in the release of nitric oxide from its reservoirs in proteins called S-nitrosothiols. Chief among these is albumin, which turns the gas into S-nitrosoalbumin.
That suggests the vitamin deficiency may trigger hoarding of nitric oxide, which in turn brings on the harmful vessel constriction.
In the latest study, reported in the June 8 issue of Circulation Research, Valerian Kagan and his colleagues at the University of Pittsburgh compared markers of nitrogen activity in 42 pregnant women, half of whom had preeclampsia, as well as a dozen women who weren't pregnant.
When measured as a fraction of blood, preeclamptic women had about 18 percent more S-nitrosothiols than normal women. The difference was even greater when calculated as a percentage of total protein, with preeclamptic women having nearly twice as much nitrogen-holding protein as healthy women.
Preeclamptic women also had markedly higher S-nitrosoalbumin, averaging roughly two and three times more than healthy pregnant and non-pregnant women, respectively.
Kagan says the obvious implication of the findings is that treating preeclamptic women with vitamin C might unlock nitric oxide and uncramp their blood vessels. "There are other ways, but vitamin C is a natural compound. You don't want to give chemicals and drugs to pregnant women."
In fact, a British study published in 1999 hinted that giving women vitamin C and vitamin E, another powerful antioxidant, may cut the risk of the disorder.
Bridget Brosnihan, a preeclampsia expert at Wake Forest University in North Carolina, says the new study fits with her own work showing that healthy mothers have elevated levels of a group of molecules, called angiotensins, that help blood vessels dilate by releasing nitric oxide. Those with the blood-pressure condition don't have this increase, but they do have more of a different form of angiotensin that keeps vessels constricted.
Dr. Alberto Nasjletti, a pharmacologist at New York Medical College in Valhalla and a spokesman for the American Heart Association, calls the findings "intriguing" and says they may have "a great deal of potential importance."
If the researchers are correct, "then you can correct the disturbance by giving back what is lacking, and what is lacking, according to their hypothesis, is vitamin C."
However, Nasjletti says it's unlikely that the study is the last word in the preeclampsia story.
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