Powerful hormones secreted by the heart may be good candidates for drugs to treat hypertension, congestive heart failure and kidney disease afflicting about 27 million Americans, researchers say.
Scientists at the University of California, San Francisco, said last week that a hormone called rat auriculin has been shown to help animals with high blood pressure, but they cautioned that it is too early to tell whether it can benefit humans.
The hormone belongs to a class of hormones known as atrial natriuretic factors or ANF, the only known hormones produced and secreted by the heart. Discovered just four years ago, they have been the subject of intense research because of their suspected importance in controlling blood pressure.
The UC scientists reported their finding of how the rat auriculin hormone works in the Journal of Clinical Investigation.
The ANF hormones are secreted naturally only by cells in the atrium of the heart when the heart stretches to accommodate an increase in blood volume.
The hormones relax the arteries and allow them to stretch, a process called vasodilation. They also increase the excretion of salt and water in the urine--known as natriuresis and diuresis, respectively--as the body attempts to bring blood volume and pressure down to normal.
"These hormones appear to be potent vasodilators and diuretics," said Dr. Martin Cogan, assistant professor of medicine at UC, San Francisco, and head of the research team. "We believe synthetic versions of these hormones could be useful in treating various ailments."
Vasodilators, which include such drugs as betablockers, and diuretics often are used to treat heart problems because they decrease blood pressure, thereby relieving stress on the heart.
'Getting Rid of Salt'
In experiments with rats, the researchers found ANF to be "a unique way of getting rid of salt," Cogan said. "In addition, it combines the properties of both a vasodilator and diuretic, and it does not decrease kidney function as do many other vasodilators and diuretics."
Rather, he said, it increases kidney function.
"These qualities could make it very useful in treating hypertension, kidney and heart problems," he said.
National Center for Health Statistics officials in Hyattsville, Md., report that 25.5 million Americans suffer from high blood pressure, 955,993 from kidney disease and 439,000 from congestive heart failure.
"Until ANF was discovered, the only known cardiac response to increased blood volume was a sympathetic nervous system response, leading to a relaxation of blood vessels and increased fluid excretion," Cogan said.
"Now there appears to be a hormonal as well as a nervous system response by the heart to changes in blood volume."
These systems seem to act in parallel, perhaps independently, to do the same thing, he said. However, many questions remain about the hormone system and how it interacts with the neural system.
"We don't yet know if ANF is involved in the pathogenesis of diseases like hypertension or congestive heart failure," he said. "And although the hormone has been shown to help hypertensive animals, no one yet knows if it will be effective in humans."