New mechanism for the beneficial effect of sildenafil on erectile function: H2S.

It has been extensively demonstrated that hydrogen sulfyde (H2S) is implicated is several physiological and pathological conditions (J Mol Med, 2012 Mar;90(3):255-63). In particular, it has been shown that H2S causes relaxation in human penile tissues (Proc Natl Acad Sci USA, 2009 Mar 17;106(11):4513-8) and inhibits phosphodiesterase (PDE) activity in vessels (ATVB 2010, Oct;30(10):1998-2004). Beside sildenafil increases H2S generation in human bladder (Eur Urol. 2012 Dec;62(6):1174-80) and tadalafil in myocardial tissues (Circulation 2009, 120:S31-S36). Therefore, our aim was to demonstrate the link between H2S and PDE-5 in mice corpus cavernosum tissues. Thus, we investigated the effects of sildenafil (10 μM, 0.5h); PDE-5 inhibitor, on H2S production as well as the H2S -induced relaxations in mice penile tissues. Penile tissues from CD1 mouse corpus cavernosum (MCC) were used. Functional studies were performed by myograph in Krebs solution. Western blot analysis was performed in order to evaluate CBS and CSE expression and methylene blue assay for measurement of H2S levels. In order to investigate functional significance of H2S on sildenafil-induced augmentation of endothelial relaxation in MCC the sildenafil effect was evaluated on acetylcholine (ACh; 10-9-10-4M), L-cysteine (10-6-10-3M) and NaHS-induced relaxations in presence or not of CSE enzyme inhibitor PPG (10 μM, 0.5h). In order to achieve this issue the H2S production in MCC tissues was also evaluated by incubating the penile tissue with sildenafil in presence or absence of the CSE inhibitor PPG (10 μM, 0.5h) Both CBS and CSE were expressed in MCC and the enzymes efficiently converted L-cysteine into H2S. Further we showed that sildenafil caused a significant increase in H2S production and this augmentation was reversed by CSE inhibition. We found that sildenafil induced an increase in both ACh and L-cysteine-induced relaxations and these augmentations reversed by CSE inhibitor PPG in MCC pre-contracted with phenylephrine (3.10-5M). Beside sildenafil did not significantly increase the NaHS -induced relaxations. Therefore we suggest that both gaseous transmitters NO and H2S affect sildenafil action. In particular our results demonstrate that sildenafil effect is partially mediated by H2S pathway. Thus, H2S signaling may represent a new mechanism involved in the effect of sildenafil on erectile dysfunction.