Viagra may relieve stomach problems.

Viagra for Diabetics?

Viagra may soon find a daytime job. A new mouse study suggests it may help relieve one of the miseries of diabetes, a chronic condition in which the stomach fails to empty after a meal. Up to 75% of all diabetics suffer from gastroparesis, a complication that can lead to bloating, nausea, and vomiting. Viagra, already a blockbuster, could find a huge new market if it performs as well in these patients as it did in diabetic mice.

It's not entirely clear why diabetics' stomachs are unable to release food into the gut, but one theory is that the sphincter muscle at the stomach's lower end won't relax properly. One reason for this might be a deficit of the gaseous neurotransmitter nitric oxide, a powerful muscle relaxant. Indeed, mice engineered to lack nitric oxide have bloated stomachs, just like diabetics. So neurobiologist and gastroenterologist Christopher Ferris and his colleagues at Johns Hopkins University set out to test whether diabetic mice also suffered from gastroparesis and, if so, whether a nitric oxide defect was the cause.

The team used mice in which the insulin-producing cells in the pancreas had been destroyed, leading to a diabetes-like condition. Compared to normal mice, the diabetics retained food in their stomachs about twice as long. What's more, the usually abundant nitric oxide-producing enzyme was virtually gone in the nerve cells innervating the intestine. But the team could completely reverse the drop in nitric oxide secretion--and restore normal food processing--by giving the mice insulin.

Human diabetics, however, often suffer from gastroparesis even if they take insulin. "We asked ourselves: How else could we treat this condition?" recalls Ferris. An obvious candidate for treating the condition was Viagra, which enhances nitric oxide signaling in blood vessels. Sure enough, diabetic mice on Viagra showed a stomach emptying rate that was indistinguishable from healthy mice, the team reports in the August issue of The Journal of Clinical Investigation. Clinical trials with Viagra in diabetes patients should start next year, Ferris says.

"The real advance of the study," says gastroenterologist Raj Goyal of the West Roxbury Veterans Affairs Medical Center and Harvard Medical School, is that it shows that diabetic mice--and possibly humans--have a deficiency in nitric oxide signaling. It would also be worth testing whether nitric oxide deficiency may be involved in stomach problems in otherwise healthy individuals, says Goyal.

Related sites
Gastroparesis and Diabetes; information from the National Institutes of Health
The Journal of Clinical Investigation

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