Back when Viagra first was marketed, some sexual health experts suggested that it might work in women as well as men, providing a pharmacological aid for women with low levels of arousal (sometimes termed "female sexual dysfunction" or "female sexual arousal disorder").

But it hasn't worked that well in women, suggesting there's something about arousal in males versus females that differs physiologically. (It does help some women: A 2008 study, for example, showed women on antidepressants who had sagging libidos were helped some by the little blue pill.)

Now scientists at Pfizer, the company that discovered Viagra's sexual effects by chance while searching for a treatment for high blood pressure and angina, say they've taken an important step in finding such a drug.

You can read about their findings, published in the British Journal of Pharmacology, in a news release titled "Towards Treating Female Sexual Dysfunction: Research Reveals Secrets of Female Sexual Arousal."

Or if you need calming down after all this sizzling sex talk, check out the research paper "UK-414,495, a selective inhibitor of neutralendopeptidase, potentiates pelvic nerve-stimulated increases in female genital blood flow in the anesthetized rabbit."

The crux of what the scientists found seems to be this:

A drug called UK-414,495 enhanced blood flow to the vaginal region when the pelvic nerve of the rabbit was stimulated. This seems to work because the drug blocks the destruction of a key nerve chemical, VIP, that helps dilate blood vessels. So it hangs around for longer to do its job.

The scientists say that the research is still in its very early stages. But two things have them encouraged: The enhanced dilation of blood vessels didn't happen all over the body (you wouldn't want that; you want the effect to be somewhat specific), and it only happened when the pelvic nerve was stimulated.

Pfizer says this particular drug isn't suitable for development, but the finding may pave the way for other drugs.

One reason Viagra has only mixed results in women may be that nitric oxide, the chemical that's affected by Viagra and that is centrally involved in male erections, isn't as major a player as VIP.

The scientists also note that "the translation of results obtained in the rabbit to humans is currently unknown."

They add that there are some studies suggesting some women with arousal disorders are helped by enhanced blood flow to the genitals.

But in the case of the most-studied drug, Viagra, "normal sexual desire appears to be critical" for it to work.