| Premature ejaculation is a very common male sexual disturbance, next to erectile dysfunction. Currently, behaviour therapy, topical anaesthetics, tricyclic antidepressants, selective serotonin reuptake inhibitors (SSRIs) are used to cure PE. However, an approved treatment does not exist. Many studies found that selective phosphodiesterase (PDE)-5 inhibitor Sildenafil (Sil) , which is mainly used in the treatment of ED, can achieve potential effectiveness in the treatment of PE. But the exact mechanisms are not illuminated. It is supposed that PDE5 exists in vas deferens, prostate, seminal vesicle,post urethra. A hypothesis considered that the possible mechanisms involved in Sildenafil for the treatment of PE might relate to the NO-cGMP signal pathway, relaxing the smooth muscle of vas deferens, prolonging the duration of erection.In this paper, the mechanisms of Sil in the treatment of PE have been elucidated from isolated organ, tissues and molecular levels, aim to provide clinical evidences.1. The relaxant effects of Sil on the rat vas deferens and its mechanismTo investigate the relaxant effects of Sil on the rat vas deferens, the changes of tension of isolated smooth muscle strips were recorded. The results showed that(1) Sildenafil (Sil) could concentration-dependently relax the smooth muscle of vas deferens contracted by electrical field stimulation(EFS) or KCl(80 mmol·L-1). Their EC50 was 9.82μmol·L-1 and 46.9μmol·L-1. But the NO donors Sodium nitroprusside (SNP) and L-argine could not affect the contraction either by EFS nor by KCl.(2) L-NAME(0.1mmol·L-1), a nitric oxide synthase (NOS) inhibitor, could attenuate the relaxation by Sil on the species which were stimulated by EFS or KCl: the maximum effect was decreased from (87.27±1.91)% to (68.02±2.29)% (p<0.05),and (87.46±3.87)% to (72.99±4.23)%(p<0.05) respectively; EC50 was increased to (45.7μmol·L-1)(p<0.05) and (63.2μmol·L-1)(p<0.05) respectively.(3) Sil (10 - 4 mol·L-1) could shift the concentration-effect curve to the right noncompetitively. The maximum effect decreased from ( 279.47±16.43 ) mg to (160.45±10.82)mg.It is suggested that Sildenafil could relax the smooth muscle of rat vas deferens directly and its mechanisms related to the NO-cGMP pathway, and also involved NO-independent way.2. Effects of Sil on cyclic GMP in the rat vas deferens in vitroTo investigate further mechanisms of action of Sil, the cGMP concentrations in the rat vas deferens were measured by 125I radioimmunoassay. The results showed that Sil increased basal cGMP concentration directly (p<0.05) and this action could be completely inhibited by L-NAME (p<0.05). In the presence of sodium nitrosside (SNP), a stimulatory agent of cGMP, Sil could increased cGMP significantly (p<0.05). It is suggested the mechanisms of treating PE of Sil involved NO-cGMP signal transduction pathway, with increasing cGMP levels, relaxing vas deferens smooth muscle .3. Effects of Sil on the mRNA expression of cGMP-binding cGMP-specific phosphodiesterase(PDE5) in rat vas deferensTo elucidate the molecular mechanism of Sildenafil, the expression of two isoforms of specific cGMP-binding phosphodiesterase 5, PDE5A1 and PDE5A2, mRNA in rat vas deferens were detected by reverse transcription-polymerase chain reaction (RT-PCR). Effects of Sil on PDE5 mRNA level were also observed. The primers used for RT-PCR were as follows. PDE5A1(345bp), upstream sequence 5ˊ- TGA TCA CCG GGA CTT TAC CT-3ˊ ; PDE5A2(327bp), upstream sequence 5ˊ- TGC TAT GTT GCC CTT TGG AG -3ˊ . Their common downstream sequence was 5ˊ- GAG CAC TGG TCC CCT TCA -3ˊ .β-actin(368bp), upstream sequence was 5ˊ- TCT ACA ATG AGC TGC GTG TG -3ˊ and downstream sequence 5ˊ- AAT GTC ACG CAC GAT TTC CC -3ˊ . After incubating with Sil for 1.5h or 3h respectively, the levels of PDE5 mRNA were examined by RT-PCR. The results showed that there were both PDE5A1 and PDE5A2 mRNA expression in rat vas deferens. Sil could obviously inhibit these two isoforms mRNA expression in rat vas deferens. The inhibitory effect of Sil on PDE5 mRNA might account for its molecular mechanisms for treating PE.ConclusionVas deferens could be relaxed by Sil and this effect might be involved about the NO-cGMP pathway and the NO-cGMP independent way. |
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