Viagra's Effect on Nerve Activity - Brief Article

The drug sildenafil citrate--better known as Viagra--causes a dramatic increase in the nerve activity associated with cardiovascular function, especially during physical and mental stress, bolstering recommendations that men with severe cardiovascular disease use caution when taking the drug. This finding comes from researchers at the University of Iowa Cardiovascular Research Center, Iowa City.
"Little is known about Viagra's effect on the cardiovascular system, particularly during situations when the cardiovascular system is under stress, as it is during sexual activity," notes Bradley G. Phillips, assistant professor in the university's College of Pharmacy. "Recent concern and reports of heart attacks, arrhythmias, and even deaths temporally related to Viagra use in patients with heart failure initially raised questions about the drug's effect on the cardiovascular system."
Researchers studied 14 healthy men, ages 25 to 39, who were given a 100mm dose of Viagra or a placebo on two separate days. Men who received Viagra on the first visit were given the placebo on their second visit and vice-versa. Neither the participants nor the researchers knew which drugs were being administered on either of the study days.
The researchers took baseline measurements of subjects' blood pressure and heart rates, noradrenaline levels, and sympathetic nerveactivity (nerve activity that causes blood vessels to constrict). The investigators took similar measurements 30 and 60 minutes after administering Viagra and the placebo while subjects rested. Immediately following the 60-minute "rest" period, each participant's cardiovascular response was evaluated during stressful conditions, including exercise, mental stress, and cold exposure.



Compared to the placebo, the researchers found that Viagra resulted in more than a doubling of sympathetic nerve activity and a 30% increase in blood levels of noradrenaline. Moreover, sympathetic nerve activity after taking Viagra increased even more dramatically during stressful conditions.
"It is well-recognized that sympathetic nerve activity is already increased in patients with cardiovascular diseases like heart failure and that this high sympathetic activity is detrimental over the long term," Phillips indicates. "Our study showed that Viagra increases this type of nerve activity at rest and even further during stressful situations. For people with unstable cardiovascular disease, this could be a problem."

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