Effects of intravesical prostaglandin E2 on bladder function are preserved in capsaicin-desensitized rats

Early Sacral Neuromodulation Prevented Detrusor Overactivity in Rats With Spinal Cord Injury

OBJECTIVES

Sacral neuromodulation (SNM) has been shown to alleviate bladder dysfunction in patients with overactive bladder and nonobstructive urinary retention. However, the therapeutic effect and mechanism of SNM in neurogenic bladder dysfunction are still not fully understood. Using a rat model of spinal cord injury (SCI), this study aims to investigate the therapeutic effect of early SNM in the bladder-areflexia phase on neurogenic bladder dysfunction and evaluate its possible mechanism.

MATERIALS AND METHODS

Basic physiological parameters such as body/bladder weight, blood pressure, and electrocardiogram results were measured to evaluate the safety of SNM. Enzyme-linked immunosorbent assays and quantitative real-time polymerase chain reaction were used to examine the expression of proinflammatory factors. Hematoxylin and eosin and Masson's trichrome staining were used to observe morphological changes, and cystometry was used to evaluate urodynamic changes after SNM treatment. Western blotting and immunofluorescence staining were used to measure the levels of transient receptor potential vanilloid 1 (TRPV1) and calcitonin gene-related peptide (CGRP) in the L6-S1 dorsal root ganglia (DRGs) and bladder. Capsaicin desensitization was used to investigate whether inhibiting TRPV1 could prevent detrusor overactivity in SCI rats.

RESULTS

Early SNM did not affect the body/bladder weight, heart rate, blood pressure, or the expression of proinflammatory cytokines (PGE2, IL-1, IL-2, IL-6, TGF-β, or TNF-α) in the bladders of SCI rats. Morphologically, early SNM prevented urothelial edema (p = 0.0248) but did not influence collagen/smooth muscle in the bladder. Compared with untreated rats with SCI, the rats treated with SNM exhibited increased bladder capacity (p = 0.0132) and voiding efficiency (p = 0.0179), and decreased nonvoiding contraction (NVC) frequency (p = 0.0240). The maximum pressure, basal pressure, postvoid residual, and NVC amplitude did not change significantly. After the SNM treatment, the expression of TRPV1 in the bladder and CGRP in L6-S1 DRGs weredecreased (L6, p = 0.0160; S1, p = 0.0024) in SCI rats. In capsaicin-desensitized SCI rats, urodynamic results showed an increase in bladder capacity (p = 0.0116) and voiding efficiency (p = 0.0048), and diminished NVC frequency (p = 0.0116), while other parameters did not change significantly.

CONCLUSIONS

Early SNM prevented urothelial edema morphologically and detrusor overactivity in SCI rats. Inhibition of TRPV1 in the bladder and DRGs may be one of the potential mechanisms for preventing detrusor overactivity by SNM.

The mast cell stimulator compound 48/80 causes urothelium-dependent increases in murine urinary bladder contractility

Mast cells and degranulation of preformed inflammatory mediators contribute to lower urinary tract symptoms. This study investigated pathways by which the mast cell stimulator compound 48/80 alters urinary bladder smooth muscle contractility via mast cell activation. We hypothesized that 1) mast cell degranulation causes spontaneous urinary bladder smooth muscle contractions and 2) these contractions are caused by urothelium-derived PGE2. Urothelium-intact and -denuded urinary bladder strips were collected from mast cell-sufficient (C57Bl/6) and mast cell-deficient (B6.Cg-Kitw-sh) mice to determine if compound 48/80 altered urinary bladder smooth muscle (UBSM) contractility. Electrical field stimulation was used to assess the effects of compound 48/80 on nerve-evoked contractions. Antagonists/inhibitors were used to identify prostanoid signaling pathways activated or if direct activation of nerves was involved. Compound 48/80 caused slow-developing contractions, increased phasic activity, and augmented nerve-evoked responses in both mast cell-sufficient and -deficient mice. Nerve blockade had no effect on these responses; however, they were eliminated by removing the urothelium. Blockade of P2 purinoreceptors, cyclooxygenases, or G protein signaling abolished compound 48/80 responses. However, only combined blockade of PGE2 (EP1), PGF2α (FP), and thromboxane A2 (TP) receptors inhibited compound 48/80-induced responses. Thus, the effects of compound 48/80 are urothelium dependent but independent of mast cells. Furthermore, these effects are mediated by druggable inflammatory pathways that may be used to manage inflammatory nonneurogenic bladder hyperactivity. Finally, these data strongly suggest that great care must be taken when using compound 48/80 to determine mast cell-dependent responses in the urinary bladder.NEW & NOTEWORTHY Urothelial cells are first responders to noxious contents of the urine. Our study demonstrates that the urothelium is not only a barrier but also a modulator of urinary bladder smooth muscle phasic activity and contractility independent of immune cell recruitment in response to an inflammatory insult.