Effect of periurethral denervation on function of the female urethra

Effects of vaginal conjugated equine estrogens and ospemifene on the rat vaginal wall and lower urinary tract

Although the positive effects of vaginal estrogens and the selective estrogen receptor modulator, ospemifene (OS), on the vaginal epithelium are well recognized, less is known regarding the effects of these therapies on the lower urinary tract or vaginal muscularis. Clinical evidence suggests that vaginally administered estrogen may improve overactive bladder-related symptoms. The objective of this study was to compare the effects of OS, vaginal conjugated equine estrogens (CEE), or both on the vaginal wall and lower urinary tract in a rat model of menopause. Contractile force of the bladder neck, dome, and external urethral sphincter at optimal field stimulation did not differ significantly among treatment groups. Pharmacologic responses to atropine, carbachol, and potassium chloride were similar among groups. Vaginal epithelial thickness and differentiation were differentially regulated by CEE or OS. Ospemifene altered epithelial differentiation pathways in vaginal epithelium in a unique way, and these effects were additive with local CEE. Unless contraindicated, the beneficial effects of vaginal CEE on the vaginal wall outweigh those of OS.

Nitrergic relaxations and phenylephrine contractions are not compromised in isolated urethra in a rat model of diabetes

In vivo experiments in a diabetic rat model revealed compromised nitrergic urethral relaxations and increased sensitivity to adrenergic agonists. This study evaluated contractile and relaxation properties of urethral smooth muscle after streptozotocin (STZ)-induced diabetes, in vitro, with the aim of determining whether in vivo deficiencies are related to smooth muscle dysfunction. Urethral tissue was collected from adult female Sprague-Dawley rats naive, STZ-treated, vehicle-treated and sucrose-fed at 9-12 week post treatment. Strips from proximal, mid, and distal urethra were placed in tissue baths and stimulated using electric field stimulation (EFS) and pharmacological agents. nNOS staining was evaluated using immunohistochemistry. Phenylephrine (PE, 10μM) contracted all urethral strips with the highest amplitude in mid urethra, in all treatment groups. Likewise, EFS-induced relaxation amplitudes were larger and were observed more frequently in mid urethra. Relaxations were inhibited by the NOS inhibitor, L-NAME (1-100μM). Sodium nitroprusside (0.01-1μM), an NO donor, reversed PE-induced contractions. No statistical differences were observed between treatment groups with respect to any parameters. Qualitative immunohistochemistry showed no differences in the urethral nNOS innervation patterns across the treatment groups. In summary, nitrergic relaxations and adrenergic-induced contractions in the isolated diabetic rat urethra display similar properties to controls, suggesting no dysfunction on the nitrergic or alpha1 adrenergic receptor function in the smooth muscle. This further implies that compromised urethral relaxation and increased adrenergic agonist sensitivity observed in vivo in this model may be due to the disruption of neural signaling between the urethra and the spinal cord, or within the CNS.

Recovery of the injured external anal sphincter after injection of local or intravenous mesenchymal stem cells

OBJECTIVES

To understand the endogenous process of wound healing after anal sphincter injury and to determine possible mechanisms by which mesenchymal stem cells (MSCs) exert their regenerative potential.

METHODS

Virginal female rats (n=204) underwent anal sphincter laceration and repair. Thereafter, animals were randomly assigned to control injection, injection with intravenous MSCs, or direct injection of MSCs into the injured sphincter. Twenty uninjured animals served as baseline controls. Sphincters were analyzed for contractile function and parameters of wound healing 24 hours, 48 hours, 7 days, and 21 days after injury.

RESULTS

Direct injection of MSCs into the injured anal sphincter resulted in improved contractile function 21 days after injury compared with controls. Although expression of both proinflammatory (cyclooxygenase-2 and interleukin-6) and anti-inflammatory (interleukin-10 and tumor necrosis factor-α-stimulated gene-6) genes were increased dramatically and transiently after injury, MSCs did not alter this response. In contrast, transforming growth factor (TFG)-β1 (an important mediator of matrix deposition by mesenchymal cells) and lysyl oxidase (an enzyme important for synthesis of collagen and elastin) expression increased dramatically at earlier time points in the direct MSC injection group compared with controls. Increased expression of TFG-β1 and lysyl oxidase in directly injected sphincters was associated with increased collagen deposition and engraftment of MSCs in the sphincter.

CONCLUSION

In this preclinical animal model, direct, but not intravenous, injection of MSCs into the injured anal sphincter at the time of repair resulted in improved contractile function of the sphincter after injury, increased matrix deposition in the external anal sphincter, and increased expression of TFG-β1 and lysyl oxidase in the acute phase after injury.

Comparison of the contractile properties, oxidative capacities and fibre type profiles of the voluntary sphincters of continence in the rat

The external urethral sphincter (EUS) and external anal sphincter (EAS) are the principal voluntary striated muscles that sustain continence of urine and faeces. In light of their common embryological origin, shared tonic sphincteric action and synchronized electrical activity in vivo, it was expected that they would exhibit similar physiological and structural properties. However, the findings of this study using paired observations of both sphincters isolated from the rat show clearly that this is not the case. The anal sphincter is much more fatigable than the urethral sphincter. On completion of a fatigue protocol, the amplitude of the last twitch of the EAS had declined to 42 +/- 3% of the first twitch, whereas the last twitch of the EUS was almost identical to that of the first (95 +/- 3%). Immunocytochemical detection of myosin heavy-chain isoforms showed that this difference was not due to the presence of more slow-twitch oxidative type 1 fibres in the EUS compared with the EAS (areal densities 4 +/- 1% and 5 +/- 1%, respectively; P = 0.35). In addition, the fatigue difference was not explained by a greater contribution to force production by fast oxidative type 2A fibres in the urethral sphincter. In fact, the anal sphincter contained a higher areal density of type 2A fibres (56 +/- 5% vs. 37 +/- 4% in the EUS, P = 0.017). The higher oxidative capacity of the EUS, measured histochemically, explained its fatigue resistance. These results were surprising because the fatigue-resistant urethral muscle exhibited faster single-twitch contraction times compared with the anal sphincter (56 +/- 0.87 ms vs. 72.5 +/- 1.16 ms, P < 0.001). Neither sphincter expressed the type 2X myosin isoform but the fast-twitch isoform type 2B was found exclusively in the EUS (areal density 16 +/- 2%). The type 2B fibres of the EUS were small (diameter 19.5 +/- 0.4 mum) in comparison to typical type 2B fibres of other muscles. As a whole the EUS is a more oxidative than glycolytic muscle. In conclusion, analysis of the twitch mechanics and fatigue of two sphincters showed that the EUS contained more fatigue-resistant muscle fibres compared with the EAS.

Effect of myogenic stem cells on contractile properties of the repaired and unrepaired transected external anal sphincter in an animal model

OBJECTIVE

To estimate the effect of myogenic stem cells on contractile function of the external anal sphincter after transection with or without repair in an animal model.

METHODS

One hundred twenty virginal female rats were randomly assigned to repair (n=60) or no repair (n=60) after anal sphincter transection. Animals were further divided into two groups: 40-microliter injection at the transection site with either phosphate-buffered solution (control) or myogenic stem cells (3.2x10 cells). Animals were killed at 7, 21, or 90 days, and the anal sphincter complex dissected and analyzed for contractile function.

RESULTS

Contractile function of the external anal sphincter was severely impaired 7 days after sphincter transection with or without repair. Twitch tension, maximal tetanic contraction, and maximal contractile force in response to electrical field stimulation improved significantly with time after sphincter repair. Injection of myogenic stem cells in the anal sphincter at the time of repair resulted in superior contractile function at both 7 days and 90 days compared with controls. Interestingly, contractile function of the nonrepaired external anal sphincter did not improve with time with or without myogenic stem cells. Indicators of denervation (fatigue and twitch or tetany ratios) did not change among groups.

CONCLUSION

In this animal model, injection of myogenic stem cells at the time of external anal sphincter repair resulted in enhanced contractile function at 90 days compared with repair alone. Without repair, function of the external anal sphincter was not improved by stem cell therapy at any time point. These results suggest that addition of myogenic stem cells improves both acute and long-term function of the external anal sphincter after mechanical injury.

Contractile properties of the denervated external anal sphincter

OBJECTIVE

The purpose of this study was to evaluate the effect of denervation on contractile properties of the external anal sphincter (EAS) of the female rat.

STUDY DESIGN

Sham operation, pudendal nerve transection, pelvic neurectomy, or combined pudendal nerve transection/pelvic neurectomy was performed in young female rats. Contractile function of the EAS was determined after 2 weeks.

RESULTS

Maximal force-generating capacity of the EAS was not impaired by bilateral pudendal denervation or pelvic neurectomy. Twitch tension, however, was decreased, and fatigability increased after pelvic neurectomy. Combined bilateral pudendal nerve-transection plus pelvic neurectomy resulted in compromised force-generating capacity, decreased twitch tension, and increased fatigability of the anal sphincter.

CONCLUSION

Subtle changes in EAS function are detectable after pelvic neurectomy, but not pudendal denervation. In contrast, combination pudendal and pelvic neurectomy resulted in severe compromise of EAS function. These data suggest that EAS function is relatively preserved unless injury occurs to > 1 source of innervation.

Physiologic role of nitric oxide and nitric oxide synthase in female lower urinary tract

PURPOSE OF REVIEW

In recent years nitric oxide (NO) has gained increasing recognition as an important neurotransmitter and cell signaling molecule with a broad range of functions in the lower urinary tract. This review discusses recently published data related to the physiologic and pathophysiologic roles of NO and nitric oxide synthase (NOS) in the female lower urinary tract.

RECENT FINDINGS

Expression of three isoforms of NOS, namely endothelial NOS, neuronal NOS and inducible NOS, has been identified in various tissues of the lower urinary tract in animals and humans. In addition to its relaxation effects on bladder and urethra, NO also serves as a neurotransmitter in the lower urinary tract. The physiologic roles of NO in overactive bladder, bladder outlet obstruction, diabetic cystopathy, interstitial cystitis, and bladder inflammation have been demonstrated.

SUMMARY

NO plays an important role in the micturition process and in disorders of the lower urinary tract. Improved understanding of the pathophysiologic role of NO/NOS system and of the L-arginine-NO-cGMP pathway may allow us to identify suitable therapeutic targets for lower urinary tract disorders. However, there is a need for further investigation to determine the precise function of NO in human lower urinary tract because most work thus far has been done in animal models.

Effect of periurethral denervation on smooth muscles of the lower urinary tract

OBJECTIVE

This study was undertaken to determine the effect of periurethral denervation on contractile function of the smooth muscle of the lower urinary tract of the female rat.

STUDY DESIGN

Periurethral nerve transection or sham operation was performed in 35 young female rats. Contractile function of the bladder dome and base was determined as a function of time after surgery. Statistical analysis was conducted by Student t test.

RESULTS

Periurethral denervation resulted in impaired contractile responses to electrical field stimulation in the bladder base (nerve-transected 45 +/- 11 g/cm 2 ; sham 84 +/- 10 g/cm 2 , P < .05) and dome (nerve-transected 179 +/- 16 g/cm 2 ; sham 334 +/- 29 g/cm 2 , P < .05) 2 weeks after nerve transection. The ability to respond to potassium chloride and the muscarinic agonist, carbachol, and the rates of contraction and relaxation, however, remained intact. Baseline phasic contractile activity was increased significantly in bladders from nerve-transected animals. Maximal field-stimulated contractions of the longitudinal urethra smooth muscle were not altered by periurethral denervation (sham 21 +/- 6 g/cm 2 , nerve-transected 19 +/- 5 g/cm 2 , P = .4). Compromised nerve-mediated contractions of the bladder dome and base improved significantly by 21 days.

CONCLUSION

Periurethral nerve transection results in transient impairment of neurogenic contractile responses in the bladder base and dome, though the intrinsic ability of the bladder to contract remains intact. This compromised response of the dome, in conjunction with previous results demonstrating impaired urethral smooth muscle relaxation, suggests that transection of periurethral neurons may have complex effects on the entire lower urinary tract.