New research shows that not only does Viagra help men overcome medical barriers to sex, it's also an aphrodisiac.

Researchers at the University of Wisconsin-Madison report this month that sildenafil, sold in the U.S. as Viagra, increases the amount of oxytocin released by the pituitary gland.

Sometimes called the "love hormone" or "cuddle chemical," oxytocin has been linked to sexual arousal and plays several important roles in social interactions and reproduction, including triggering uterine contractions and lactation. It is also released during orgasm.

The finding is the first indication that erectile dysfunction drugs like Viagra may have physical effects in addition to increasing blood flow to sexual organs, said study author Meyer Jackson, a physiology professor at the UW-Madison School of Medicine and Public Health, in a news release.

Oxytocin release is regulated by an enzyme that acts like a braking system, limiting hormone release by dampening neural excitation of the cells. This same enzyme, phosphodiesterase type 5, also limits blood flow by contracting the muscles around blood vessels.

In both places, sildenafil works by blocking this enzyme, essentially releasing the brakes put on the oxytocin, said Jackson.

"The same stimulation will produce more (oxytocin) release," he said. "I think this is a missing link in terms of trying to sort out the issues around whether there are additional effects of phosphodiesterase type 5 inhibitors," which include Viagra, Levitra and Cialis.

The new report was published online Aug. 9, appears in an upcoming issue of the Journal of Physiology.

In the study, the scientists measured oxytocin released from rat pituitaries in response to neural stimulation. When the pituitaries were treated with sildenafil, they responded to the stimulation by releasing three times as much oxytocin as they did without the drug.

Importantly, the drug had little if any effect on hormone release in the absence of stimulation, Jackson said.

"Erectile dysfunction drugs do not induce erections spontaneously, they enhance the response to sexual stimulation," he said. "The same thing is happening in the posterior pituitary - Viagra will not induce the release of oxytocin on its own, but it will enhance the amount of release you get in response to electrical stimulation."

Though sildenafil's effects on these pathways are still unknown, work by other researchers has shown that oxytocin-sensitive cells in the brain play a role in the neural control of erectile responses, suggesting that Viagra and its kin may work through multiple channels.

The study, said Jackson, shows that blue pills could have other uses as well. Oxytocin has been linked to the ability to make strong social bonds. Another recent study showed that sildenafil helped hamsters overcome jetlag.

"This is one piece in a puzzle in which many pieces are still not available," Jackson added. "But it raises the possibility that erectile dysfunction drugs could be doing more than just affecting erectile dysfunction."