Maryland researchers who have been on a decade-long search for the chemical agent that causes hypertension and drugs to control it said yesterday they have found strong evidence the culprit is a hormone secreted by the adrenal gland.
Scientists at the University of Maryland Medical Center said that they observed that levels of the hormone ouabain (pronounced WAH-bane) rose as a patient's blood pressure rose and fell as the patient's pressure fell. In patients whose pressure was normal, ouabain levels did not fluctuate.
"Perhaps in a few years, people at cocktail parties may be talking about ouabain levels in the same way they talk about their cholesterol levels," Dr. Mordecai P. Blaustein, professor and chairman of physiology, said yesterday.
Hypertension, or high blood pressure, is a disorder that afflicts 60 million Americans. It is a leading cause of heart attack, stroke, and kidney failure.
Overproduction of ouabain by the adrenal glands appears to increase the concentration of calcium in cells that line blood vessels, causing them to constrict and heighten blood pressure, Dr. Blaustein said.
A recent study, first disclosed at last month's meeting of the Endocrine Society, involved nine patients with a peculiar form of hypertension and 11 patients without any blood pressure problem. The nine patients developed hypertension when they had their thyroid glands removed because of thyroid cancer. In those patients, ouabain levels increased when their blood pressure shot up and dropped as soon as the patient took a thyroid replacement drug that lowered his blood pressure.
Larger studies will be needed to prove that ouabain is the culprit behind hypertension, the scientists said. One now under way involves hundreds of patients with "essential hypertension," the type that afflicts more than 90 percent of all people with high blood pressure.
Admitting that it was speculative to talk about new treatments before any are found, scientistssaid isolating the agent that causes hypertension is crucial to developing better drugs to control it. Drugs now on the market lessen the symptoms but do not attack the cause.
And while the drugs keep many people alive, he said, they work unevenly from person to person and cause many side effects.
Dr. John Hamlyn, a physiologist who developed a blood test for ouabain, said he found extremely high concentrations of the hormone in the adrenal glands of cows, sheep, horses, rats, cats -- and people. "Basically, everything that seems to walk on four legs, even sea turtles," Dr. Hamlyn said.
A discussion of the animal study appeared in yesterday's issue of Proceedings of the National Academy of Sciences.
Ouabain is chemically indistinguishable from digitalis, a plant extract that has been given for two centuries to control heart ailments like congestive heart failure and certain abnormal heart rhythms, like the one that recently afflicted President Bush. Toxic levels also have been used to make poison darts in South America and Africa.