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CORVALLIS, Ore. - A natural compound found in Oregon grape and many other plants - as well as in many over-the-counter herbal remedies - is potentially dangerous for heart patients, a new study suggests.

The compound berberine has many natural sources, including a popular Chinese herb called huang lian. It slows heart cell contractions that keep the organ beating, said researcher Theresa Filtz, an associate professor of pharmaceutical sciences at Oregon State University and one of the authors on the study.

Used in over-the-counter herbal remedies for a variety of ailments, berberine acts directly on "muscarinic receptors" in cardiac cells to alter heart rate, her laboratory experiments revealed.

"Muscarines" are powerful cardiac depressants found in certain mushrooms. When these compounds are ingested, they activate the muscarinic receptors - proteins that help regulate heart rate. Berberine activates these same receptors, stimulating similar effects, found Filtz and lead author Satin Salehi, a Ph.D. graduate of the College of Pharmacy. These findings raise a red flag for consumers who use herbal remedies without a doctor's supervision, the researcher said.

"If you have congestive heart failure, for example, you don't want to be stimulating your muscarinic receptors," Filtz cautioned.

The Chinese herbal mixture huang lian, which contains berberine, is widely used as a home remedy to treat everything from aching legs, arthritis and carpal tunnel to mumps, pneumonia and tennis elbow. But given berberine's effects, using it to self-medicate is potentially harmful, particularly for people with serious heart disease, said Filtz.

"Just because compounds come from plants, they're not safe by default," she said. "They can have some very strong chemicals in them."

The berberine study, which will be published in an upcoming issue of Pharmacological Research, is a follow-up to another recent OSU investigation of the active compounds in hawthorn. Occurring naturally in the hawthorn tree, hawthorn extract is another natural substance that affects heart function.

Hawthorn extract, which has been used for centuries as an alternative therapy for cardiovascular disease, "has been shown to have various effects on heart rate," Filtz and her colleagues noted in the Journal of Natural Medicine in 2009.

Their studies to uncover the chemical mechanisms at work showed that, like berberine, hawthorn's effects on heart rate - including arrhythmia and hypotension in high doses - are consistent with muscarinic receptor activation. Their research on the compound is ongoing.