Potent inhibition of human phosphodiesterase PDE-5 Icariin derivatives
During sexual stimulation, nitric oxide is released into the corpus cavernosum causing an erection. Nitric acid activates an enzyme (guanylate cyclase) which increases levels of cyclic guanosine monophosphate (cGMP). Cyclic GMP leads to smooth muscle relaxation in blood vessels supplying the corpus cavernosum resulting in increased blood flow and erection.
Pressure from the expanding penis compresses the veins that drain blood from the penis, trapping blood in the corpus cavernosum and sustaining the erection. The erection is reversed when cGMP levels in the corpus cavernosum fall causing the smooth muscle of the corpus cavernosum to contract, stopping the inflow of blood and opening veins that drain blood away from the penis. Levels of cGMP fall because it is destroyed by phosphodiesterase-5 (PDE-5).
Of the four plant extracts traditionally used for male impotence; (Tribulus terrestris, Epimedium brevicornum (Horny goat Weed), Ferula hemonis, Cinnamomum cassia) only the Epimedium brevicornum extract Icariin was active in inhibiting phosphodiesterase-5A1 (PDE5-A1). Acting as a PDE-5 inhibitor icariin blocks the degradation of phosphodiesterase-5 on cGMP in smooth muscle cells lining the blood vessels leading to the corpus cavernosum thus sustaining the erection.
Tribulus terrestris may work by relaxing smooth muscles and increasing blood flow to the corpus cavernosum. This relaxant effect is likely due to increased release of nitric oxide from nerve endings and skin cells in the penis. Studies in Bulgaria and Russia indicate that tribulus increases blood levels of testosterone, DHEA (a hormone building block), and estrogen. Additionally, Tribulus terrestris contains protodiocin which is also believed to boost the production of libido producing hormones such as testosterone.
Ferula hemonis has been prescribed by Arab physicians as an aphrodisiac for both men and women for centuries. It is believed to function as a restorative tonic to strengthen the overall health of the being, to improve impotence and increase desire.
The constituents feroline and ferutinine are believed to increase the production of testosterone and balance estrogen levels. Ferutinine alone has been found to improve luteinizing hormone (LH). In men, LH stimulates the testicles to produce greater levels of testosterone which increases sex drive, motivation, mood and general wellbeing.
This study demonstrates that the active constituent of Horny goat Weed, Icariin, potently inhibits phospohodisesterase-5A1 as effectively as sildenafil. Resulting in increased duration of erections with less cellular toxicity.