Objentives : This study was aimed to evaluate the cavernosal relaxation effect of Crataegii fructus(CF) in the contracted rabbit penile corpus cavernosum by agonists.

Methods : In order to study the effect of CF on the vasoconstriction of rabbit penile corpus cavernosum, isolated rabbit penile corpus cavernosum tissues were used for the experiment using organ baths containing Krebs solution.
To investigate the cavernosal relaxation of CF, CF extract at 0.01 ～ 3.0 ㎎/㎖ was added after penile corpus cavernosum were contracted by norepinephrine(NE) 1 μM.
To analyze the mechanism of CF''s vasorelaxation, CF extract infused into contracted penile tissues by NE after each treatment of indomethacin(IM), Nω-nitro-L-arginine(L-NNA), methylene blue(MB), tetraethylammonium chloride(TEA).
To study the effect of CF on influx of extracellular calcium chloride(Ca2+) in penile tissues, in Ca2+-free krebs solution, Ca2+ 1 mM infused into contracted penile tissues by NE after pretreatment of CF.
Cytotoxic activity of CF on human umbilical vein endothelial cell(HUVEC) was measured by MTT assay, and nitric oxide(NO) prodution was measured by Griess reagent.

Results : CF relaxed cavernosal strip with endothelium contracted by NE, but in the strips without endothelium, CF-induced relaxation was significantly inhibited.
The pretreatment of L-NNA, MB, TEA decreased significantly on the cavernosal relaxation than not-treatment of them. But the pretreatment of IM had no significant effect on the cavernosal relaxation.
In Ca2+-free krebs solution, when Ca2+ infused into contracted penile tissues by NE, pretreatment of CF inhibit contraction induced by adding Ca2+.
NO production wasn''t increased by treatment of CF on HUVEC.

Conclusions : This findings showed that CF is effective for the relaxation of rabbit penile corpus cavernosum, and we suggest that CF relax rabbit corpus cavernosal smooth muscle through multiple action mechanisms that include increasing the release of nitric oxide from corporal sinusoidal endothelium, inhibition of Ca2+ mobilization into cytosol from the extracellular fluid, and maybe a hyperpolarizing action.