A recent article in Science News (reg req’d) summarizes several areas of medical research in which PDE-5 inhibitors are being used to treat problems relating to poor blood circulation. PDE-5 (phosphodiesterase-5) is an enzyme that causes blood vessels to constrict, thus reducing flow. Viagra and other drugs such as Cialis increase blood flow to a man’s sexual organ by inhibiting the enzyme’s effects.

The Science News article lists the following areas in which sildenafil citrate (Viagra) is showing promise:

• Pulmonary hypertension (high blood pressure in the lungs)—Dr. Tilman Humpl found that sildenafil citrate enabled children with this disease to be more active and to live longer.
• Chronic Heart Failure—Dr. Marco Guazzi found that sildenafil enabled patients with this disease to metabolize more oxygen during exercise.
• Cardiac Pressure Overload—Researchers artificially constricted the main artery leading out of a mouse’s heart, which usually causes the heart to significantly grow in size (hypertrophy) and also reduces the amount of blood pumped out with each heartbeat. Mice treated with sildenafil had no reduction in volume pumped nor did their hearts enlarge.
• Chemotherapy—The anti-cancer drug doxorubicin damages heart cells, but the damage was prevented in mice that were given both doxorubicin and sildenafil.
• Liver Disease—Problems with the liver can lead to elevated levels of ammonia in the blood, which causes impaired mental abilities. Rats with this problem were given sildenafil and later outperformed non-treated rats in maze navigation.
• Kidney Disease—Sildenafil relieved the symptoms of a rare kidney disease known as nephrogenic diabetes insipidus, in rats.
• Preeclampsia (not enough blood to uterus)—A research team found that sildenafil treatment for pregnant rats with preeclampsia-like symptoms produced healthier pups and improved uterine blood vessel growth.
• Fetal Growth Restriction (not enough blood to uterus)—Sildenafil caused restricted blood vessels to widen in pregnant women with FGR.
• Heart Attacks—Sildenafil reduced the amount of heart damage by half in rabbits with simulated heart attacks. This would be useful during heart surgery, where it’s possible that blood flow to the heart may be interrupted.

Sildenafil is well on its way to becoming a miracle drug of sorts, and it definitely shows promise in quite a few areas. It is not, however, approved by the FDA for use other than erectile dysfunction and pulmonary hypertension. Of especial importance is that we don’t know the long-term effects of taking sildenfal on a daily basis. Viagra is not intended to be taken continuously and was not tested for day-by-day use.