Epimedium viagra similarity

Like Viagra, icariin, the active compound in Epimedium, inhibits the activity of PDE-5. In vitro assays have demonstrated that icariin inhibits PDE-5 with an IC50 of around 1 micromolar, while Viagra has an IC50 of about 6.6 nanomolar (.0066 micromolar) and Levitra has an IC50 of about 0.7 nanomolar (.0007 micromolar). Measured differently, the EC50 of icariin is approximately 4.62 micromolar, while Viagra is .42 micromolar. Epimedium has been shown to up-regulate genes associated with nitric oxide production and changes in adenosine/guanine monophosphate balance in ways that other PDE5 inhibitors do not.

A phosphodiesterase type 5 inhibitor, often shortened to PDE5 inhibitor, is a drug used to block the degradative action of phosphodiesterase type 5 on cyclic GMP in the smooth muscle cells lining the blood vessels supplying the corpus cavernosum of the penis. These drugs are used in the treatment of erectile dysfunction. Because PDE5 is also present in the arterial wall smooth muscle within the lungs, PDE5 inhibitors have also been explored for the treatment of pulmonary hypertension, a disease in which blood vessels in the lungs become abnormally narrow.

Smooth muscle is fundamentally different from skeletal muscle and cardiac muscle in terms of structure and function.
Smooth muscle fibers are spindle shaped, and like all muscle, can contract and relax. In the relaxed state, each cell is spindle-shaped, 20-500 micrometers long and 5 micrometers wide.

Smooth muscle cells can be stimulated to contract or relax in many different ways. They may be directly stimulated by the autonomic nervous system ("involuntarily" control), but can also react on stimuli from neighbouring cells and on hormones.