※ 引述《lyddite (苦味酸炸药)》之铭言： : 附带一下 : 在九三年的考古有出现 : 威而刚是何种ligand引起的 : 我发现我在p16并没有写 : 查了一下 : PDE 5增加海绵体平滑肌对氧化氮（Nitric oxide）的作用，使平滑肌放松 : 答案应该是NO 补一下.... The physiologic mechanism of erection of the penis involves release of nitric oxide (NO) in the corpus cavernosum during sexual stimulation. NO then activates the enzyme guanylate cyclase, which results in increased levels of cyclic gua-nosine monophosphate (cGMP), producing smooth muscle relaxation in the corpus cavernosum and allowing inflow of blood. Sildenafil has no direct relaxant effect on isolated human corpus cavernosum, but enhances the effect of nitric oxide (NO) by inhibiting phosphodiesterase type 5 (PDE5), which is responsible for degradation of cGMP in the corpus cavernosum. When sexual stimulation causes local release of NO, inhibition of PDE5 by sildenafil causes increased levels of cGMP in the corpus cavernosum, resulting in smooth muscle relaxation and inflow of blood to the corpus cavernosum. Sildenafil at recommended doses has no effect in the absence of sexual stimulation. 其实「那个」的时候会促进 NO 的释放 NO促进 soluble guanosine cyclase，使 GTP转成 cGMP 最後 cGMP 会被 PDE水解 sildenafil的作用是抑制 PDE5 ，增加 cGMP 的量而达到效果 --

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