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

Abstract

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.

Keywords: Sildenafil; external sphincter function; lower urinary tract; mice; phosphodiesterase type 5.

Figure 1

Sildenafil increases bladder compliance, reduces voiding threshold and increases EUS bursting. (A) Representative recordings of bladder pressure and EUS‐EMG activity in the DAPM before and after administration of sildenafil (10 and 30 pm) to the perfusate. (B) Sildenafil significantly decreased the threshold pressure (P = 0.029) and increased bladder compliance (P = 0.011). Sildenafil significantly increased the number of bursts of EUS‐EMG activity per void compared with baseline (P = 0.023) and vehicle control recordings (at 30 pm, P = 0.033). Repeated measures anova with Dunnett's test for multiple comparison. *P < 0.05 compared to baseline; ^# P < 0.05 compared to vehicle, unpaired t‐test.

Figure 2

Peripheral actions of sildenafil. (A) Recordings of bladder pressure changes in response to saline infusion were made in the pithed DAPM. (B) Administration of sildenafil (30 pm) to the perfusate increased bladder compliance, which led to a consequent increase in the volume infused before the maximum pressure threshold was reached (15 mmHg). Repeated‐measures anova with Dunnett's test for multiple comparisons *P < 0.05: difference from baseline.

Figure 3

Sildenafil increases bladder afferent activity. (A) Pelvic nerve recording of afferent activity showed a ramping increase with bladder filling and this declined to a plateau during an isovolumetric storage phase. Sildenafil (10 and 30 pm) augmented afferent activity during both phases. (Bi) Sildenafil (10 and 30 pm) increased pelvic afferent activity during the filling phase referenced against bladder pressure. (Bii) Proportionate change in afferent firing across bladder pressures caused by sildenafil compared to vehicle control, in each case normalised to the baseline bladder fill‐evoked activity. (Ci) Sildenafil (10 and 30 pm) significantly increased pelvic afferent activity even after stopping saline infusion into the bladder and losing the dynamic component of bladder wall stretch (P = 0.002), and standardised values of afferent firing rate by baseline showed significant difference compared to vehicle group (Cii). *P < 0.05, **P < 0.01 difference from baseline, related‐samples Friedman's one‐way anova by ranks. ^# P < 0.05, ^## P < 0.01 difference from vehicle, Mann–Whitney U‐test.

Figure 4

Sildenafil increases EUS bursting in vivo, an effect not mediated by altered EUS contractility. (A) Representative recording of bladder pressure and EUS‐EMG activity in urethane‐anaesthetised mouse showing systemic (i.p.) administration of sildenafil 14 ng/kg (~30 pm) increasing the number of EUS bursts. (B) Pooled normalised data showing sildenafil significantly increased the EUS‐EMG activity during voiding compared to both baseline and to vehicle group. (C) Representative recording of tetanic contractions of whole EUS induced by EFS after administration of sildenafil (10 and 30 pm) and the NO donor, SNP (100 μm) to the perfusate. Note that sildenafil had no effect on contractility, whereas it was markedly reduced by SNP. (D) Plots of maximum amplitude and AUC of EFS‐induced contraction showed no change after sildenafil administration (10, 30 and 300 pm), and both were significantly reduced by SNP (100 μm). *P < 0.05, **P < 0.01 difference from baseline, related‐samples Friedman one‐way anova by ranks. ^# P < 0.05 difference from vehicle, Mann–Whitney U‐test.