Blood pressure is the force exerted by blood on the walls of the arteries. When the pressure is too high, the heart is working harder than it should, and the blood vessels are overstressed. High blood pressure, or hypertension, can range from mild to severe. Physicians knew for a long time that very high blood pressure was harmful, but it took the results of a long-term study of the residents of Framingham, Massachusetts, to convince doctors in the early 1960s that all hypertension was dangerous. It can lead to heart attack, stroke, and kidney failure. Researchers also announced in 1998 that high blood pressure could mean a higher risk of developing dementia. Hypertension affects sixty million, or nearly one out of four, Americans.

Attempts to find effective ways to treat hypertension led researchers to uncover the methods by which the body regulates blood pressure; knowledge of that process is...