NEW YORK (Reuters Health) - US researchers have identified a protein that seems to play a key role in regulating erections in rats. They hope that a compound that blocks the protein may lead to an alternative treatment for erectile dysfunction in humans.

The protein, called rho-kinase, is part of a biological chain-reaction that acts on muscle, ``keeping the penis flaccid--thereby preventing erections,'' co-author Dr. Christopher J. Wingard, of the Medical College of Georgia in Augusta, told Reuters Health.

After identifying the Rho-kinase pathway as one that helps to maintain the normal state of a flaccid penis, the researchers injected rats with a compound known to inhibit the protein's activity.

The result? The compound, dubbed Y-27632, blocked the reaction and caused the rats to have erections, Wingard said. His team reports their findings in detail in the January issue of Nature Medicine.

Achieving an erection relies on increased blood flow into two spongy chambers in the penis. But in some men--including about half of those over 40--arterial disease leads to reduced blood flow into the penis. Arterial disease is common in patients with heart disease and diabetes.

The naturally occurring chemical nitric oxide plays an important role in regulating this blood flow, Wingard explained.

``Most (impotence) treatments have been designed to manipulate the nitric oxide pathway. This is the method of action that the erectile dysfunction drug Viagra uses to help men with impotence,'' Wingard pointed out.

However, up to 40% of men with erectile dysfunction have not found Viagra to be beneficial, Wingard noted, and this is the group he and his colleagues hope to help.

As of now, Y-27632 has proven effective in rats only by way of direct injection into the penis, a procedure not expected to be popular with most men.

``Currently, we are looking at other ways of applying the compound either orally (in pill form) or perhaps topically,'' Wingard said.

SOURCE: Nature Medicine 2001;7:119-122.