PubMed · 10772598
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C G McMahon. 2000-02-21. Sildenafil.. https://doi.org/10.5694/j.1326-5377.2000.tb125557.x
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Phosphodiesterase-5 (PDE5) inhibitors (sildenafil, vardenafil, or tadalafil) or phosphorylation by cyclic nucleotide-dependent protein kinase causes an apparent conformational change in PDE5, as indicated by a shift in migration on non-denaturing PAGE gels and an altered pattern of tryptic digestion. Combination of cGMP and a PDE5 inhibitor or phosphorylation does not cause a further gel shift or change in tryptic digest. Phosphorylation of PDE5 is stimulated by inhibitors, and combination of cGMP and inhibitor does not cause further phosphorylation. Dephosphorylation of PDE5 by either purified phosphoprotein phosphatase-1 or -2A catalytic subunit or by a crude phosphatase mixture is not affected by cGMP or inhibitors, suggesting that phosphorylation itself maintains conformational exposure of the phosphorylation site. The combined results imply that cGMP binding to the catalytic site initiates negative feedback control of many cellular cGMP signaling pathways by directly stimulating phosphorylation and activation of PDE5; by exploiting this molecular mechanism, PDE5 inhibitors stimulate their own potencies.
The diagnosis and treatment of erectile dysfunction has changed dramatically since the availability of safe and effective oral therapies. Unfortunately, not all men can be adequately treated in this way, and might require more invasive testing to diagnose and treat the specific cause of their dysfunction. This review looks at the tests and strategies available for men who cannot be treated by oral therapy alone.
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