FRIDAY, Sept. 30 (HealthDay News) — Efforts to develop a new class of chronic arthritis medications using a painkiller compound naturally produced by the body have fallen short, researchers say.

A new animal-based study has shown that endomorphin, the morphine-like pain control agent in question, does not have any “observable effect” on reducing the sensitivity of arthritic joint nerves in the long run.

The therapy did, however, provoke a dramatic reduction — upwards of 75 percent — in short-term joint hypersensitivity.

“I don’t think it’s all negative news,” said study co-author Jason J. McDougall, an associate professor in the department of physiology and biophysics at the University of Calgary in Alberta, Canada. “We were able to block pain responses in normal joints and also in the early stages of arthritis. But clearly arthritis is a chronic long-term disease, so we were obviously disappointed that we weren’t able to block the pain of long-term inflammation.”

The mixed findings come against the backdrop of last year’s ban by the U.S. Food and Drug Administration on sales of the popular cox-2 inhibitors Vioxx and Bextra due to an increased risk for cardiovascular complications associated with long-term use. The removal of the drugs has limited pain management options for millions of Americans, although a third cox-2 drug — Celebrex — has been allowed to remain on the market with new packaging that highlights potential risks.

In this context, the authors described the excitement that has recently greeted the identification of two forms of endomorphin, a painkiller, or analgesic, naturally produced by the body.

Scientists student loan calculator have agreed that endomorphins are, theoretically, at least as powerful a tool for pain management as morphine, a problematic narcotic derived from the opium poppy.

The authors stressed that morphine is notoriously difficult to administer with precision — provoking a wide range of side-effects like cardio-respiratory depression, severe constipation, nausea, and a manic-depressive disorder known as dysphoria.

On the other hand, researchers have previously found that endomorphins are able to sidestep such concerns by virtue of their hard-wired relationship to the body’s own pain control receptors. Such receptors, known as u-opioids, appear to be highly sensitized to endomorphins, selectively drawing the natural analgesic to their target spots throughout the peripheral tissue of joints.

In the October issue of Arthritis and Rheumatism, the researchers say these findings have raised hopes that the body’s home-made painkiller might be the most beneficial means for helping the one-third of the world’s adult population who suffer from some form of arthritic pain.

To explore their potential, McDougall and his colleagues looked at the effect of “endomorphin 1” — the most common and potent of the two known endomorphins– on both acute and chronic arthritis in male lab rats.

After inducing inflammation in their right knee joints, the researchers treated the rats with endomorphin 1 at various points following the onset of knee arthritis — either 48 hours post-inflammation during the acute stage of joint pain, or at the one-week or three-week point during the chronic stage.

At all stages of treatment, the authors measured the electrical activity, or firings, of knee nerve-endings in response to an exaggerated rotation of the joint. Nerve-ending readings were also taken among rats that did not have arthritic knees but were nonetheless also treated with endomorphin.

The researchers found that endomorphin treatment caused nerve activity — and presumably any related pain — to drop off by approximately 75 percent in both normal rats and those with acute arthritis of the knee.

However, when injected one or three weeks after the onset of arthritis, endomorphi