Effects of Sildenafil, a Phosphodiesterase Type 5 Inhibitor, on the Primary Single Afferent Activity of the Rat Bladder

Inhibition of PDE-4 isoenzyme attenuates frequency and overall contractility of agonist-evoked ureteral phasic contractions

The aim of this study was to investigate the functional role of phosphodiesterase enzymes (PDE) in the isolated porcine ureter. Distal ureteral strips were mounted in organ baths and pre-contracted with 5-HT (100 μM). Upon generation of stable phasic contractions, PDE-4 and PDE-5 inhibitors were added cumulatively to separate tissues. PDE-4 inhibitors, such as rolipram (10 nM and greater) and roflumilast (100 nM and greater), resulted in significant attenuation of ureteral contractile responses, while a higher concentration of piclamilast (1 μM and greater) was required to induce a significant depressant effect. The attenuation effect by rolipram was abolished by SQ22536 (100 μM). PDE-5 inhibitors, such as sildenafil and tadalafil, were not nearly as effective and were only able to suppress the 5-HT-induced contractions at higher concentrations of 1 μM. Rolipram significantly enhanced the depressant effect of forskolin, while sodium nitroprusside-induced attenuation of contractile responses remained unchanged in the presence of tadalafil. In summary, our study demonstrates that PDE-4 inhibitors are effective in attenuating 5-HT-induced contractility in porcine distal ureteral tissues, while PDE-5 inhibitors are less effective. These findings suggest that PDE-4 inhibitors, such as rolipram, may hold promise as potential therapeutic agents for the treatment of ureteral disorders attributable to increased intra-ureteral pressure.

Sildenafil corrects the increased contractility of rat detrusor muscle induced by alprostadil in vitro

BACKGROUND

Sildenafil (PDE5-inhibitor) and alprostadil (PGE₁) are used in combination clinically for the management of some cases of erectile dysfunction. Despite the roles of prostaglandins (PG) and nitric oxide (NO) pathways in contractility of bladder smooth muscle are frequently studied, the effect of sildenafil/alprostadil combination and the crosstalk between NO/cGMP and PG pathways on bladder activity is not documented.

METHODS

Organ-bath experiments were performed using isolated rat detrusor muscle. Direct and neurogenic contractions were induced using ACh and electric stimulation (EFS, 4Hz, 80V, 1ms), respectively. The contractile responses in absence and presence of the tested drugs at different concentrations were compared. Results are expressed as mean ± SEM (n = 5-7).

RESULTS

Alprostadil (0.01-10 μM) concentration-dependently potentiated ACh (100μM)- and EFS (4 Hz)- induced contraction. Maximum potentiation of ACh-contraction in presence of alprostadil was 40 ± 5%. Sildenafil potentiated ACh-induced contraction at low concentrations (0.01-1 μM), but inhibited it at higher ones (10-100 μM). IBMX (non-selective PDE-inhibitor, 0.01-100μM) and SNP (NO-donor, 1nM-1 mM) produced the same biphasic pattern. The potentiatory phase of sildenafil was inhibited by atropine (0.1μM), L-NAME (non-selective NOS-inhibitor, 100μM), N-PLA (nNOS-inhibitor, 30μM) or MB (nonselective GC-inhibitor, 10μM). In presence of sildenafil (0.1μM), the concentration-response curve of alprostadil (0.01-10μM) on both ACh and EFS-induced contraction was clearly shifted downward.

CONCLUSIONS

A crosstalk between PGE₁ and NO/cGMP pathways may exist. At low concentrations only, the effect of sildenafil on bladder contractility is dependent on NO/cGMP. cGMP intracellularly-elevated by sildenafil, may inhibit the activity of PLC and hence the cascade of EP₁-receptors, thus masking the hyperactivity of bladder caused by alprostadil, which adds to the advantages of this combination.

Sildenafil, a phosphodiesterase type 5 inhibitor, augments sphincter bursting and bladder afferent activity to enhance storage function and voiding efficiency in mice

Objectives

To investigate the influence of low‐dose sildenafil, a phosphodiesterase type 5 inhibitor (PDE5‐I), on the function of the mouse lower urinary tract (LUT).

Materials and Methods

Adult male mice were decerebrated and arterially perfused with a carbogenated Ringer's solution to establish the decerebrate arterially perfused mouse (DAPM). To allow distinction between central neural and peripheral actions of sildenafil, experiments were conducted in both the DAPM and in a ‘pithed’ DAPM, which has no functional brainstem or spinal cord. The action of systemic and intrathecal sildenafil on micturition was assessed in urethane‐anaesthetised mice.

Results

In the DAPM, systemic perfusion of sildenafil (30 pm) decreased the voiding threshold pressure [to a mean (sem) 84.7 (3.8)% of control] and increased bladder compliance [to a mean (sem) 140.2 (8.3)% of control, an effect replicated in the pithed DAPM]. Sildenafil was without effect on most voiding variables but significantly increased the number of bursts of the external urethral sphincter (EUS) per void in DAPM [to a mean (sem) 130.1 (6.9)% of control at 30 pm] and in urethane‐anaesthetised mice [to a mean (sem) 117.5 (5.8)% of control at 14 ng/kg]. Sildenafil (10 and 30 pm) increased pelvic afferent activity during both bladder filling and the isovolumetric phase [to a mean (sem) 205.4 (30.2)% of control at 30 pm]. Intrathecal application of sildenafil (5 μL of either 150 pm or 1.5 nm) did not alter cystometry and EUS‐electromyography variables in urethane‐anaesthetised mice.

Conclusions

Low‐dose sildenafil increases bladder compliance, increases pelvic nerve afferent activity, and augments the bursting activity of the EUS. We propose that the novel actions on afferent traffic and sphincter control may contribute to its beneficial actions to restore storage and voiding efficiency in LUT dysfunction.