Roanoke Times
                 Copyright (c) 1995, Landmark Communications, Inc.

DATE: SATURDAY, March 23, 1991                   TAG: 9103230070
SECTION: NATIONAL/INTERNATIONAL                    PAGE: A-2   EDITION: METRO 
SOURCE: Associated Press
DATELINE: NEW YORK                                LENGTH: Medium

BLOOD-CLOTTING PROTEIN FOUND

The protein binds to a natural substance called thrombin as the initial step in producing blood clots, which can cause heart attacks and strokes when they block blood vessels.

The discovery was reported Friday in the journal Cell by researchers at the University of California, San Francisco. Further research may lead to new medicines that block formation of blood clots without the side effects of current drugs, study co-author Dr. Shaun Coughlin said Friday.

The scientists reported that they had isolated the genetic material that lets cells produce the protein, called a thrombin receptor. The receptor sits on the surface of blood cells called platelets.

Thrombin, which is produced by blood vessels in response to injury, binds to this receptor. That makes platelets clump together, which is the initial step in clot formation, Coughlin said in a telephone interview.

The scientists showed that the newfound protein made cells respond to thrombin. They also deduced the chemical makeup of the protein.

Drugs that block the binding of thrombin to the receptor may be able to prevent formation of clots with fewer side effects that current thrombin-inhibiting medications, Coughlin said. That is because such drugs would not block beneficial effects of thrombin that do not require the receptor, he said.

Those effects include causing production of another protein that discourages clot formation, he said. Normally that anti-clot action appears to be important in regulating thrombin's effects, although its importance in blocking clots that lead to strokes and heart attacks is not known, he said.

The thrombin receptor also appears on smooth muscle cells that line blood vessels and play a role in atherosclerosis, a narrowing of the passageway for blood within arteries that sets the stage for heart attacks and strokes. Thrombin stimulates growth of the cells.

Doctors often treat atherosclerosis by removing the bumpy plaques on the inside of the blood vessels. But sometimes the arteries become narrowed again because of growth of the smooth muscle cells. The new finding may aid research into this process, Coughlin said.