The herbal supplement St. John's wort may help control pain linked to hypersensitive bladder disorders such as interstitial cystitis (IC), according to a new study involving rats.

Bladder hyperactivity -- characterized by frequent contractions -- is a significant cause of bladder irritation and pain.

In the study, researchers at the University of Pittsburgh Medical Center injected a formulation of St. John's wort called DP015 into the abdomens of rats with bladder inflammation.

They found that the treatment resulted in longer intervals between bladder contractions. The findings were expected to be presented Tuesday at the American Urological Association annual meeting, in Atlanta.

Prior research found that neural control of the lower urinary tract is controlled by serotonin- and norepinephrine-emitting neurons. These are similar to neurons that play a role in anxiety and depression.

"St. John's Wort is an herbal supplement that has been used for years to treat symptoms of mild depression, while urologists often use antidepressants to treat interstitial cysts," researcher Dr. Michael B. Chancellor, a professor of urology and gynecology, said in a prepared statement.

"Given that the supplement and the drug work on the same systems, it makes sense that St. John's wort could help treat this painful disease," Chancellor said.

IC affects an estimated 700,000 Americans (90 percent of them women), according to the U.S. National Institute of Diabetes and Digestive and Kidney Diseases.