The erectile dysfunction drug sildenafil, better known as Viagra, seems to increase the pituitary gland's production of the hormone oxytocin, report researchers from the University of Wisconsin-Madison. Known as the "love hormone" or "cuddle chemical," oxytocin plays several important roles in social interactions and reproduction, including triggering uterine contractions and lactation. It is also released during orgasm and has been linked to sexual arousal.
The finding is the first indication of a chemical mechanism through which erectile dysfunction drugs like Viagra may have physical effects besides increasing blood flow to sexual organs, says study author Meyer Jackson, a physiology professor at UW-Madison.
Sildenafil seems to boost oxytocin by increasing blood flow to the posterior pituitary. "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 [Viagra, Levitra and Cialis]," said Jackson.
The new study, appearing in the Journal of Physiology, involved measuring 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 doesn't think his findings raise any significant safety issues related to Viagra use, but 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 noted. 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 little 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. "It raises the possibility that erectile dysfunction drugs could be doing more than just affecting erectile dysfunction," mused Jackson.
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Source: University of Wisconsin-Madison
