Sperm kinematics of normozoospermic specimens after stimulation by varying concentrations of a specific inhibitor of CGMP phosphodiesterase type-5 (Sildenafil)

Abstract

Objectives: Cyclic nucleotides (cAMP and cGMP) are involved in sperm motility, capacitation, and in the acrosome reaction of many animal species. It is known that human sperm motility can be enhanced by cyclic adenosine monophosphate (cAMP) phosphodiesterase (PDE) inhibitors. This study investigated whether the direct addition of sildenafil, a specific inhibitor of cGMP PDE type-5, to the ejaculates of normal men can enhance sperm kinematics.Design: Semen specimens were divided into four equal aliquots: the first received no treatment (control) and the others were incubated with 0.001microM, 0.01microM and 0.1microM of sildenafil (Pfizer, Sandwich, UK) for 1 hour. After treatment, all aliquots were processed by the swim-up technique and underwent further in vitro incubation for 3 hours.Materials and Methods: IRB approval was obtained for this study. Semen samples were obtained from 21 healthy subjects with proven fertility. Each specimen was split and treated as described above. Each aliquot was evaluated for percent motility, curvilinear velocity (VCL), straight-line velocity (VSL), average path velocity (VAP), amplitude of lateral head displacement (ALH) and hyperactivation (HYPER) using a computer assisted semen analyzer (CASA). Sperm kinematics was assessed immediately after sildenafil treatment and after swim-up and in vitro incubation. Analysis of variance (ANOVA) was used to test for statistical differences in sperm motion characteristics.Results: All motion parameters, except VSL and percent motility, were significantly increased after sperm treatment by sildenafil at the concentration of 0.01microM (P<0.03). Curvilinear velocity, ALH and HYPER were also significantly increased at the concentration of 0.1 microM (P<0.03). No effects were observed at the sildenafil concentration of 0.001microM. A dose-dependent effect of the type-5 PDE inhibitor on sperm motion characteristics was not observed. Sperm motion parameters were not statistically different between treated and control aliquots after swim-up and in vitro incubation.Conclusions: This study suggests that direct addition of sildenafil, a specific cGMP PDE type-5 inhibitor, to ejaculates of normal men enhances sperm motion characteristics. The concentration of 0.01microM seems to be optimum to improve motility, which is lower than the one found in the human ejaculate after acute administration of 100mg oral sildenafil. Our results indicate that sildenafil was not able to maintain the initial motility improvement over time after removal of the seminal plasma by swim-up in normal sperm. Objectives: Cyclic nucleotides (cAMP and cGMP) are involved in sperm motility, capacitation, and in the acrosome reaction of many animal species. It is known that human sperm motility can be enhanced by cyclic adenosine monophosphate (cAMP) phosphodiesterase (PDE) inhibitors. This study investigated whether the direct addition of sildenafil, a specific inhibitor of cGMP PDE type-5, to the ejaculates of normal men can enhance sperm kinematics. Design: Semen specimens were divided into four equal aliquots: the first received no treatment (control) and the others were incubated with 0.001microM, 0.01microM and 0.1microM of sildenafil (Pfizer, Sandwich, UK) for 1 hour. After treatment, all aliquots were processed by the swim-up technique and underwent further in vitro incubation for 3 hours. Materials and Methods: IRB approval was obtained for this study. Semen samples were obtained from 21 healthy subjects with proven fertility. Each specimen was split and treated as described above. Each aliquot was evaluated for percent motility, curvilinear velocity (VCL), straight-line velocity (VSL), average path velocity (VAP), amplitude of lateral head displacement (ALH) and hyperactivation (HYPER) using a computer assisted semen analyzer (CASA). Sperm kinematics was assessed immediately after sildenafil treatment and after swim-up and in vitro incubation. Analysis of variance (ANOVA) was used to test for statistical differences in sperm motion characteristics. Results: All motion parameters, except VSL and percent motility, were significantly increased after sperm treatment by sildenafil at the concentration of 0.01microM (P<0.03). Curvilinear velocity, ALH and HYPER were also significantly increased at the concentration of 0.1 microM (P<0.03). No effects were observed at the sildenafil concentration of 0.001microM. A dose-dependent effect of the type-5 PDE inhibitor on sperm motion characteristics was not observed. Sperm motion parameters were not statistically different between treated and control aliquots after swim-up and in vitro incubation. Conclusions: This study suggests that direct addition of sildenafil, a specific cGMP PDE type-5 inhibitor, to ejaculates of normal men enhances sperm motion characteristics. The concentration of 0.01microM seems to be optimum to improve motility, which is lower than the one found in the human ejaculate after acute administration of 100mg oral sildenafil. Our results indicate that sildenafil was not able to maintain the initial motility improvement over time after removal of the seminal plasma by swim-up in normal sperm.