Sildenafil (Viagra) is used to treat erectile dysfunction in men. It is also used to improve the ability to exercise in adults with pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the lungs). Sildenafil treats PAH by relaxing the blood vessels in the lungs to allow blood to flow easily and it treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation. Sildenafil works by promoting nitric oxide dependent smooth muscle relaxation.
The NOS3 gene encodes endothelial nitric oxide synthase. This enzyme produces nitric oxide, which is involved in vascular smooth muscle relaxation. Variations in this gene are also associated with susceptibility to coronary spasm.
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