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Effects of icariin on cGMP-specific PDE5 and cAMP-specific PDE4 activities.

AIM
To clarify the mechanism of the therapeutic action of icariin on erectile dysfunction (ED).


METHODS
PDE5 was isolated from the human platelet and PDE4 from the rat liver tissue using the FPLC system (Pharmacia, Milton Keynes, UK) and the Mono Q column. The inhibitory effects of icariin on PDE5 and PDE4 activities were investigated by the two-step radioisotope procedure with [(3)H]-cGMP/[(3)H]-cAMP. Papaverine served as the control drug.


RESULTS
Icariin and papaverine showed dose-dependent inhibitory effects on PDE5 and PDE4 activities. The IC(50) of Icariin and papaverine on PDE5 were 0.432 micromol/L and 0.680 micromol/L, respectively and those on PDE4, 73.50 micromol/L and 3.07 micromol/L, respectively. The potencies of selectivity of icariin and papaverine on PDE5 (PDE4/PDE5 of IC(50)) were 167.67 times and 4.54 times, respectively.


CONCLUSION
Icariin is a cGMP-specific PDE5 inhibitor that may be developed into an oral effective agent for the treatment of ED.