Inhibition of PDE-4 and PDE-5 Differentially Modulates Isolated Porcine Urethral Contractility

This study explores the role of phosphodiesterase (PDE) inhibitors (specifically PDE-4, PDE-5 and PDE-1) in modulating the contractility of the porcine urethral smooth muscle and mucosal layers.

Using an organ bath setup, the effects of PDE inhibitors rolipram, roflumilast, sildenafil, tadalafil and vinpocetine (0.1 nM to 10 μm) on isolated porcine urethral mucosa-intact smooth muscle, mucosa-denuded smooth muscle and mucosal layers were investigated.

Our results demonstrate that PDE-4 inhibitors (rolipram and roflumilast) significantly relaxed mucosa-intact urethral smooth muscle and reduced spontaneous contraction rates in the mucosal strips. Conversely, PDE-5 inhibitors (sildenafil and tadalafil) relaxed smooth muscle tissues denuded of mucosa but required exogenous source of nitric oxide (sodium nitroprusside) for effectiveness in relaxing the mucosa-intact tissues. PDE-1 inhibitor vinpocetine exhibited negligible effects.

The results from the study suggest a potential role of the cAMP pathway in modulating spontaneous contractions within the urethral mucosa, while the NO/cGMP pathway appears to be important in modulating urethral smooth muscle tonic contractions. These findings suggest differential roles of PDE isoenzymes in urethral tissues.