Functional responses of isolated human seminal vesicle tissue to selective phosphodiesterase inhibitors

OBJECTIVES To further elucidate the significance of the cyclic nucleotide-mediated signal transduction, we examined the in vitro functional responses of isolated seminal vesicle (SV) smooth muscle tissue to selective phosphodiesterase (PDE) inhibitors. METHODS Using the organ bath technique, the effects of increasing concentrations (1 nM to 10 AM) of the PDE inhibitors vinpocetine (PDE1 inhibitor), rolipram PDE4 inhibitor), and sildenafil and vardenafil (PDE5 inhibitors) on the tension induced by 10 AM of norepinephrine on SV tissue strips were investigated. To examine the drug effects on the tissue levels of cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP), the SV strips were exposed to different concentrations of the compounds (0.1, 1, and 10 AM). After freezing, homogenization, and extraction of cyclic nucleotides, cAMP and cGMP were measured using radioimmunoassays. In the experiments, sodium nitroprusside and forskolin were used as reference compounds. RESULTS The norepinephrine-induced tension was reversed by the drugs in a dose-dependent manner. The rank order of efficacy was rolipram greater than sildenafil greater than vardenafil greater than or equal to vinpocetine greater than sodium nitroprusside greater than forskolin. The reversion of the norepinephrine-induced tension at maximum drug concentration ranged from 79% (rolipram) to 32% (forskolin). Only rolipram and sildenafil reached a median effective concentration. The effects of the PDE inhibitors were paralleled by a 1.7-fold to 173-fold increase in tissue cGMP or cAMP. CONCLUSIONS Our results have demonstrated that PDE inhibitors can reverse the adrenergic tension of human SV tissue and increase levels of cyclic nucleotides. This outlines the potential significance of cAMP and cGMP in the control of SV smooth muscle function. These findings might be of importance with regard to the pharmacologic treatment of premature ejaculation.