"In a relatively short-term study, we've shown that this drug has a significant effect on the stiffness of the most central of blood vessels--the aorta--which is the biggest artery in your body," says lead author Gary F. Mitchell, M.D.

"Up to 50 million people in the United States have high blood pressure and over 90 percent of those people have elevated systolic pressures, which is predominantly due to increased stiffness of the larger arteries. Furthermore, only 25 percent of all patients have their blood pressure controlled with currently available medication," says Mitchell.

"Up to this time, we've only had limited understanding of how various blood pressure lowering drugs affect arterial stiffness," he adds. "Large artery stiffening was thought to be a natural irreversible part of aging. This study clearly demonstrates that the stiffness in large arteries can be reduced and that the reduction in stiffness is beyond what would be seen using drugs that lower blood pressure by other mechanisms."

Researchers studied 167 patients with moderate hypertension in a 12-week double-blind trial called Conduit Hemodynamics of Omapatrilat International Research Study (CHOIRS). Participants were randomly assigned to treatment with enalapril or the investigational drug omapatrilat, a vasopeptidase inhibitor.

Like an angiotensin converting enzyme inhibitor, the omapatrilat molecule blocks production of angiotensin II. In addition, omapatrilat also blocks breakdown hormones that cause vessels--especially large arteries--to dilate, becoming less stiff, Mitchell explains.

The researchers used pulse pressure to compare the two treatments. Elevated pulse pressure is one indication of stiffening of the large central vessels, Mitchell says, adding that studies by his group and others have shown that increased pulse pressure strongly predicts myocardial infarction, congestive heart failure, stroke and cardiovascular mortality.

As a reference, normal blood pressure, which is 120/80 millimeters of mercury (mm Hg), translates to a pulse pressure of 40 mm Hg. In the current study, the researchers first measured blood pressure in the arm. Omapatrilat reduced such peripheral pulse pressures by 8.2 mm Hg, whereas enalapril reduced pressures by 4 mm Hg. Omapatrilat was even more effective at reducing aortic pulse pressure: a drop of 10.2 mm Hg versus a 3.2 mm Hg. Investigators demonstrated that the reductions in pulse pressure were attributable to a reduction in central aortic stiffness.

patrilat reduced central pulse pressure pretty remarkably," says Mitchell. The two compounds had similar side effect rates, the researchers report.