The nitric oxide diffuses into the nearby smooth muscle cells, and activates guanylate cyclase, which converts GTP molecules to cGMP.

一氧化氮扩散到附近的平滑肌细胞，激活鸟苷酸环化酶，将GTP分子转化为cGMP。

These medications inhibit the PDE-5 enzyme in endothelial cells which normally breaks down cGMP, leading to higher levels of cGMP.

这些药物抑制内皮细胞中的PDE-5酶，而PDE-5酶通常用来降解cGMP；药物作用下，细胞内cGMP水平升高。