The new report was published online Aug. 9 and 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 says. "Erectile dysfunction drugs do not induce erections spontaneously, they enhance the response to sexual stimulation," he says. "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 he doesn't think his findings raise any significant safety issues related to Viagra use, he does think it provides strong rationale for studies of additional effects and new potential uses. "A big question raised by our study is, will sildenafil do the same thing to the nerve terminals that release oxytocin [in the brain]"" he says. The cells that supply oxytocin to the pituitary come from a brain structure called the hypothalamus, which also sends hormones throughout the brain.
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 famous blue pills could have other uses as well. Oxytocin has been linked to the ability to make strong social bonds, while sildenafil was recently shown to improve hamsters' abilities to adjust the timing of their internal clocks to overcome simulated jet lag. "This is one piece in a puzzle in which many pieces are still not available," Jackson says. "But it raises the possibility that erectile dysfunction drugs could be doing more than just affecting erectile dysfunction."
