※ 引述《lyddite (苦味酸炸藥)》之銘言： : 附帶一下 : 在九三年的考古有出現 : 威而剛是何種ligand引起的 : 我發現我在p16並沒有寫 : 查了一下 : PDE 5增加海綿體平滑肌對氧化氮（Nitric oxide）的作用，使平滑肌放鬆 : 答案應該是NO 補一下.... 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. 其實「那個」的時候會促進 NO 的釋放 NO促進 soluble guanosine cyclase，使 GTP轉成 cGMP 最後 cGMP 會被 PDE水解 sildenafil的作用是抑制 PDE5 ，增加 cGMP 的量而達到效果 --

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