20 April 2009

Male impotence drugs beneficial for some women with sexual dysfunction

by Kate Melville

The main drugs used to treat male impotence appear to also benefit around 40 percent of women who report sexual dysfunction, suggesting that the medical community should perhaps take a second look at their potential as a viable treatment for women. In a study into the effect of the PDE5 drugs Viagra, Levitra and Cialis on the pudendal arteries that supply the penis, vagina and clitoris with blood, Medical College of Georgia (MCG) researchers showed the drugs relax the arteries in both male and female rats.

"It shows the drugs need to be investigated more for women and small alterations could make these compounds more effective for women living with these disorders," said MCG's Dr. Kyan J. Allahdadi, who presented the findings at the 122nd Annual Meeting of the American Physiological Society.

Early clinical trials with PDE5 drugs found essentially no response in women, but MCG researchers decided to look again, first giving a drug to constrict the internal pudendal arteries in male and female rats - as they would be in a non-erect state - then giving doses of each impotency drug to see the impact.

The arteries from male rats displayed a relatively standard concentration-dependent relaxation - the more drug they got, the more they relaxed - while in females arteries, there was an initial relaxation then an unusual oscillation between relaxation and contraction with subsequent dosing.

While the researchers don't fully understand the female swing, they speculate that it may be the smooth muscle cells in the internal pudendal arteries of females communicating and agreeing to contract and relax, while male smooth muscle cells make independent decisions to just relax. Interestingly, they found one other distinction: females were more sensitive to Viagra (sildenafil), while males were most sensitive to Levitra (vardenafil).

The researchers noted that previous studies on the effectiveness of PD5 drugs focused on the cavernosal tissue, or penis. The internal pudendal artery actually feeds the penile artery which is buried deep in the penis where numerous caverns enable it to be flaccid when not engorged with blood. Physical stimulation of the area causes the tissue, endothelial cells and nerves to release nitric oxide, a powerful dilator of blood vessels. The system works much the same way in the vagina and clitoris.

"[PDE5 drugs] may be useful in the treatment of female sexual dysfunction caused by inadequate blood supply through the internal pudendal artery. The significant difference in how male and female pudendal arteries react to PDE5 inhibitors merits further study," said Dr. Allahdadi. The study team is now exploring the different relaxation profile observed between female and male rat internal pudendal arteries as well as functional abnormalities in internal pudendal arteries from diabetic rats.

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Source: Medical College of Georgia