Spinal and peripheral mechanisms contributing to hyperactive voiding in spontaneously hypertensive rats

Discovery of Diphenyl Ether Derivatives as Novel BKCa Channel Activators: Structure-Activity Relationship, Cryo-EM Complex Structures, and In Vivo Animal Studies

The BKCa channel, a large-conductance calcium-activated potassium channel, plays a crucial role in maintaining the homeostasis of the micturition cycle and airway-related functions. In this study, we optimized a novel BKCa channel activator, 4d, with a diphenyl ether structure identified from library screening. This led to the discovery of potent activators, 10b (EC50 = 0.12 μM, cell-based assay) and 51b, an orally bioavailable derivative. Compound 10b demonstrated potent in vivo efficacy in a spontaneous hypertensive rat (SHR) of urinary incontinence model, while compound 51b showed dose-dependent cough suppression efficacy with an ED50 of 11.8 mg/kg in a citric acid-induced cough model. Furthermore, we reported the cryo-electron microscopy (cryo-EM) structures of the BKCa channel in complex with 10b and 51b at resolutions of 2.8 and 3.4 Å. Based on structural analyses, we determined the binding sites and key interaction residues of 51b, which were validated via mutation studies.

Association of diabetes, hypertension, and their combination with basal symptoms and treatment responses in overactive bladder patients

Introduction: Pelvic hypoperfusion caused by atherosclerosis has been proposed as a cause of lower urinary tract dysfunction including overactive bladder syndrome (OAB). Limited data indicate that OAB patients with concomitant diabetes or hypertension, known risk factors of atherosclerosis, may exhibit greater baseline OAB symptoms and slightly smaller therapeutic responses to treatment, but the impact of a combined presence of diabetes and hypertension has not been reported. Therefore, we have explored whether the combined presence of both comorbidities is associated with greater baseline OAB symptoms than that of either comorbidity alone. Secondary questions were exploration of the impact of either comorbidity on baseline symptoms, and of the impact of either comorbidity alone and their combination on therapeutic responses.

Methods: Data from two non-interventional studies applying treatment with propiverine ER 30 or 45 mg/d for 12 weeks were analyzed.

Results: Number of urgency episodes in the combination group was greater than with each comorbidity alone. The impact of comorbidities on baseline intensity of incontinence, frequency or nocturia or Patient Perception of Bladder Condition was less consistent or absent. Either comorbidity alone was associated with a smaller % improvement of symptoms, and their combination had a greater effect than either alone. However, all attenuations associated with comorbidity were small relative to the overall improvement.

Conclusions: We conclude that comorbidities of diabetes and hypertension have detectable effects on OAB symptoms and treatment responses, but the small magnitude of these alterations does not justify changing existing paradigms for the clinical management of OAB.

Weak association between arterial hypertension and overactive bladder baseline symptoms and treatment responses

While animal studies have suggested an association between the presence of hypertension and the presence and/or severity of overactive bladder syndrome (OAB) symptoms, little clinical data is available. We have conducted a pre-specified secondary analysis of a non-interventional study involving 4450 OAB patients being treated with solifenacin to explore the existence of an association between OAB and hypertension using three parallel and overlapping definitions of hypertension to enhance robustness of analysis. Regardless of definition, patients with hypertension were older and had greater OAB symptom severity in univariate analyses. In multiple regression models including age as explanatory covariate, most relationships held up but effect sizes of concomitant hypertension on OAB severity were small (odds ratios <1.35 in all cases) and were deemed to be unlikely of clinical relevance. % Changes in symptom severity were somewhat smaller in univariate analysis, but effect sizes were small. We conclude that OAB and arterial hypertension are associated but effect sizes are too small to justify adaptation of clinical practice for OAB patients with concomitant hypertension.

Protective effects of hydrogen sulfide pretreatment on cyclophosphamide-induced bladder dysfunction in rats via suppression of bladder afferent nerves

Cyclophosphamide (CYP), a broad-spectrum anticancer drug, causes serious side effects, such as haemorrhagic cystitis (HC). Hydrogen sulfide (H₂S), an endogenous gasotransmitter, has physiological properties, including anti-inflammation, anti-oxidation, and neuromodulation. In this study, we investigated the effects of NaHS (H₂S donor) pretreatment on bladder dysfunction in CYP-treated rats. Male Wistar rats were intraperitoneally pretreated with NaHS (3 or 10 μmol/kg) or vehicle once daily for 7 days before cystometry, and CYP (150 mg/kg) or saline was intraperitoneally administered 2 days before cystometry. After cystometry, the bladder tissues were collected for haematoxylin and eosin staining. In some rats, capsaicin (CAP), which can desensitise CAP-sensitive afferent nerves, was subcutaneously injected at 125 mg/kg 4 days before cystometry. CYP reduced intercontraction intervals (ICI) and bladder compliance (Comp) and increased the number of non-voiding contractions (NVCs) compared with the saline-treated control group. NaHS pretreatment dose-dependently improved the CYP-induced these changes. In bladder tissues, CYP increased histological scores of neutrophil infiltration, haemorrhage, and oedema, while NaHS had no effect on these CYP-induced changes. CAP showed a tendency to suppress CYP-induced changes in ICI. NaHS-induced improvement in CYP-induced changes in urodynamic parameters were not detected in CAP-treated rats. These findings suggest that NaHS pretreatment prevented bladder dysfunction in CYP-treated rats by suppressing CAP-sensitive bladder afferent nerves, but not by suppressing bladder inflammation. Therefore, H₂S represents a new candidate as a protective drug for bladder dysfunction induced by HC, a side effect of CYP chemotherapy.

l-Theanine Protects Bladder Function by Suppressing Chronic Sympathetic Hyperactivity in Spontaneously Hypertensive Rat

Chronic sympathetic hyperactivity is known to affect metabolism and cause various organ damage including bladder dysfunction. In this study, we evaluated whether l-theanine, a major amino acid found in green tea, ameliorates bladder dysfunction induced by chronic sympathetic hyperactivity as a dietary component for daily consumption. Spontaneously hypertensive rats (SHRs), as an animal model of bladder dysfunction, were divided into SHR-water and SHR-theanine groups. After 6 weeks of oral administration, the sympathetic nervous system, bladder function, and oxidative stress of bladder tissue were evaluated. The mean blood pressure, serum noradrenaline level, and media-to-lumen ratio of small arteries in the suburothelium were significantly lower in the SHR-theanine than in the SHR-water group. Micturition interval was significantly longer, and bladder capacity was significantly higher in the SHR-theanine than in the SHR-water group. Bladder strip contractility was also higher in the SHR-theanine than in the SHR-water group. Western blotting of bladder showed that expression of malondialdehyde was significantly lower in the SHR-theanine than in the SHR-water group. These results suggested that orally administered l-theanine may contribute at least partly to the prevention of bladder dysfunctions by inhibiting chronic sympathetic hyperactivity and protecting bladder contractility.

Voiding behavior in awake unrestrained untethered spontaneously hypertensive and Wistar control rats

The spontaneously hypertensive rat (SHR), a genetic model of high blood pressure, has also been studied as a potential model of overactive bladder. In vivo studies have confirmed the presence of surrogate markers of overactive bladder, including detrusor overactivity, increased urinary frequency, decreased bladder capacity and voided volume (VV), and afferent hypersensitivity to bladder irritation. However, these observations were during awake cystometry using implanted bladder catheters tethered to an infusion pump and artificially filled. We conducted experiments in awake unrestrained untethered age-matched female SHRs and Wistar rats to quantify naïve consumption and voiding behavior and the effect of capsaicin desensitization on consumption and voiding behavior. Food and water consumption, body weight, voiding frequency, and VV were recorded. Rats were placed in metabolism cages for 24 h, up to twice a week, from 17 to 37 wk of age. Compared with Wistar rats, SHRs exhibited decrease in VV and did not exhibit diurnal variation in VV between light and dark periods, suggesting that SHRs may have bladder hypersensitivity. Furthermore, SHRs may also have smaller bladder capacities, as they consumed less water, voided less volume (regardless of light cycle), and had equal urinary frequencies compared with age-matched Wistar rats. We detected no change in SHR voiding behavior following capsaicin desensitization, which was in contrast to a prior awake in vivo cystometry study describing increased VV and micturition interval in SHRs and suggests that C-fiber activity may not contribute to bladder hypersensitivity in SHRs.NEW & NOTEWORTHY We characterized the long-term (20 wk) voiding, defecation, and consumption behavior of age-matched spontaneously hypertensive and Wistar rats without the influence of anesthesia or catheters. Spontaneously hypertensive rats exhibited bladder hypersensitiviy that persisted for the 20-wk duration and was unaffected by capsacin desensitization.

Age-related differences in responses to hydrogen sulfide in the bladder of spontaneously hypertensive rats

OBJECTIVES

To investigate whether a response to hydrogen sulfide donors (GYY4137 and sodium hydrosulfide) and the endogenous hydrogen sulfide system (hydrogen sulfide level and expression of cysteine aminotransferase, cystathionine β-synthase, cystathionine γ-lyase, and 3-mercaptopyruvate sulfurtransferase) in the spontaneously hypertensive rat bladder differ with age, we compared the responses of hydrogen sulfide donors to micturition and bladder relaxation, and the endogenous hydrogen sulfide system in the bladder of 18-week versus 12-week-old spontaneously hypertensive rats.

METHODS

GYY4137 was intravesically administered and cystometry was performed in anesthetized rats. The responses of sodium hydrosulfide were evaluated in carbachol-mediated precontracted bladder strips. Bladder hydrogen sulfide levels and expression levels of each enzyme were investigated using the methylene blue method and Western blotting, respectively.

RESULTS

GYY4137 treatment significantly prolonged intercontraction intervals only in 12-week-old rats. Sodium hydrosulfide-induced bladder relaxation was significantly attenuated in the strips of 18-week-old rats compared with that in 12-week-old rats. In the bladder dome, significant increases in hydrogen sulfide levels and in the expression of cystathionine β-synthase, 3-mercaptopyruvate sulfurtransferase, and cysteine aminotransferase were observed in 18-week-old rats compared with 12-week-old rats. However, cystathionine γ-lyase bands were not detected in bladder tissues of either group.

CONCLUSIONS

Bladder relaxation induced by hydrogen sulfide may be attenuated in spontaneously hypertensive rats in an age-dependent manner.

Silodosin improves functional consequences of lower urinary tract obstruction secondary to benign prostate hypertrophy, a proof of concept study in the spontaneously hypertensive rat supplemented with testosterone

Background

The main purpose of this study is to investigate the effect of silodosin on the urodynamic consequences in a previously established model of lower urinary tract symptoms associated with benign prostate hyperplasia, the spontaneously hypertensive rats (SHR) supplemented with testosterone.

Methods

Three groups of animals (8-week-old; n = 10/group) were considered: Wistar Kyoto (control) rats (WKY), SHR supplemented with testosterone at 3 mg/kg/day and treated with either vehicle (SHR-T, n = 10) or silodosin at 0.1 mg/kg/day (SHR-T + silodosin, n = 10) by oral gavage for 6 weeks. Cystometry experiments were performed. The bladder was harvested, weighed and paraffin-embedded for morphometric analysis. The prostate was also harvested and weighed.

Results

The number of animals included in the analysis were n = 10/10 for WKY and n = 7–8/10 for each SHR rats supplemented with testosterone group. SHR-T displayed a significant decrease in the intercontraction interval, infused volume and mean flow rate whereas the frequency of non-voiding contractions was increased. Silodosin improved the voiding behavior of SHR-T by significantly increasing the intercontraction interval, the infused volume and the mean flow rate and decreasing the number of non-voiding contractions. SHR-T displayed a significant increase in prostate and bladder weights and a 15% increase in the detrusor wall area compared to WKY.

Conclusions

Chronic silodosin treatment relieved storage symptoms in SHR supplemented with testosterone and decreased the frequency of non-voiding detrusor contractions during the filling phase.

Urodynamic Parameters in Spinal Cord Injury-Induced Neurogenic Bladder Rats after Stem Cell Transplantation: A Narrative Review

Neurogenic bladder (NGB) secondary to spinal cord injury (SCI) is accompanied with several complications such as urinary tract deterioration, urinary incontinence, and consequently lower quality of life (QoL), significant morbidities, and occasionally death. Current therapeutic methods have some side effects and there is no treatment for the upper urinary tract injuries. Stem cell therapy is a promising method for treating this condition. However, the best timing and the best route of its transplantation have not yet been determined. Animal models of SCI, especially in rats, are the most commonly used method for evaluating the efficacy of cell therapy in NGB improvement, and the most common assessment method is the urodynamic studies (UDS). However, there are variations in the range of UDS parameters among the published studies. The current review aimed to discuss the effect of stem cell transplantation on bladder dysfunction recovery based on urodynamic parameters after SCI in rats. For this purpose, the cell source, doses, the route of administration, and the complete UDS equipment and its parameters were summarized in SCI models in rats. In some urodynamic test results, to some extent, an improvement in the lower urinary system function was observed in each treatment group. However, this improvement was far from full functional recovery. The average cell dose was about 1 million cells in every injected site. In most studies, the stem cells (SCs) were transplanted 9 days after the injury using PE-50 and PE-60. Many researchers have recommended further experimental and clinical studies to confirm this treatment modality.

[Roles of endogenous hydrogen sulfide in the bladder and prostate]

Recently, hydrogen sulfide (H₂S) has been recognized as the third gasotransmitter besides nitric oxide and carbon monoxide, and it has been reported that H₂S exhibits various physiological functions such as neuromodulation and vasorelaxation. In the lower urinary tract (bladder and prostate), it is reported that donors of H₂S induce contraction of the rat detrusor and relaxation of the pig bladder neck. These reports suggest a possibility that H₂S may have site-specific effects on the bladder. However, the detailed functions of H₂S in each part of the bladder are still unclear. In addition, there is no report showing physiological roles of H₂S in the prostate. In this article, we will review the distribution of enzymes related to H₂S biosynthesis and physiological roles of H₂S in the lower urinary tract based on reports from our and other groups. We will also introduce a possibility that H₂S can be a new therapeutic target against lower urinary tract symptoms (LUTS) based on our data from spontaneously hypertensive rats (SHRs), which develop hypertension-mediated LUTS.

Hydrogen sulfide-induced relaxation of the bladder is attenuated in spontaneously hypertensive rats

PURPOSE

To compare hydrogen sulfide (H₂S)-induced relaxation on the bladder between normotensive and spontaneously hypertensive rat (SHR), we evaluated the effects of H₂S donors (GYY4137 and NaHS) on the micturition reflex and on the contractility of bladder tissues. We also investigated the content of H₂S and the expression levels of enzymes related to H₂S biosynthesis [cystathionine β-synthase (CBS), 3-mercaptopyruvate sulfurtransferase (MPST), and cysteine aminotransferase (CAT)] in the bladder.

METHODS

Eighteen-week-old male normotensive Wistar rats and SHRs were used. Under urethane anesthesia, the effects of intravesically instilled GYY4137 (10^-8, 10^-7 and 10^-6 M) on the micturition reflex were evaluated by cystometry. The effects of NaHS (1 × 10^-8-3 × 10^-4 M) were evaluated on carbachol (10^-5 M)-induced pre-contracted bladder strips. Tissue H₂S content was measured by the methylene blue method. The expression levels of these enzymes were investigated by Western blot.

RESULTS

GYY4137 significantly prolonged intercontraction intervals in Wistar rats, but not in SHRs. NaHS-induced relaxation on pre-contracted bladder strips was significantly attenuated in SHRs compared with Wistar rats. The H₂S content in the bladder of SHRs was significantly higher than that of Wistar rats. CBS, MPST and CAT were detected in the bladder of Wistar rats and SHRs. The expression levels of MPST in the SHR bladder were significantly higher than those in the Wistar rat bladder.

CONCLUSION

H₂S-induced bladder relaxation in SHRs is impaired, thereby resulting in a compensatory increase of the H₂S content in the SHR bladder.

Protein kinase C modulates frequency of micturition and non-voiding contractions in the urinary bladder via neuronal and myogenic mechanisms

Background

Protein Kinase C (PKC) dysfunction is implicated in a variety of smooth muscle disorders including detrusor overactivity associated with frequency and urgency of micturition. In this study, we aimed to evaluate the modulatory effects of endogenous PKC-dependent pathways on bladder storage and emptying function.

Methods

We utilized in vivo cystometry and in vitro organ bath studies using isolated bladder muscle strips (BMS) from rats to measure contractility, intravesical pressure, and voided volume. Both in vitro and in vivo results were statistically analyzed using one-way repeated measures ANOVA between the groups followed by Bonferroni’s post-test, as appropriate (Systat Software Inc., San Jose, CA).

Results

Effects of PKC activators, phorbol-12,13-dibutyrate (PDBu), and phorbol-12,13-myristate (PMA), were concentration-dependent, with high concentrations increasing frequency of micturition, and sensitivity of intramural nerves to electrical field stimulation (EFS), in vitro, while lower concentrations had no effect on BMS sensitivity to EFS. The PKC inhibitors, bisindolylmaleimide1 (Bim-1), (28 nM), and Ro318220 (50 μM) triggered an increase in the number of non-voiding contractions (NVC), and a decrease in the voided volume associated with reduced ability to maintain contractile force upon EFS, but did not affect peak force in vitro. Both low (50 nM) and high PDBu 1 micromolar (1uM) decreased the sensitivity of BMS to carbachol. Application of a low concentration of PDBu inhibited spontaneous contractions, in vitro, and Bim-1-induced NVC, and restored normal voiding frequency during urodynamic recordings in vivo.

Conclusions

In summary, the effects of low PKC stimulation include inhibition of smooth muscle contractile responses, whereas high levels of PKC stimulation increased nerve-mediated contractions in vitro, and micturition contractions in vivo. These results indicate that endogenous PKC signaling displays a concentration-dependent contraction profile in the urinary bladder via both smooth muscle and nerve-mediated pathways.

The urinary bladder of spontaneously hypertensive rat demonstrates bladder hypertrophy, inflammation, and fibrosis but not hyperplasia

AIMS

The present study aims to systemically characterize the factors that are associated with urinary bladder organ enlargement in spontaneously hypertensive rats (SHR).

MAIN METHODS

We compared the SHR to age-matched normotensive Wistar-Kyoto (WKY) control rats in the levels of bladder pro-inflammatory factors, collagen expression (type I), and detrusor smooth muscle growth.

KEY FINDINGS

Our results showed that enhanced inflammatory responses and fibrosis were key factors that were closely associated with bladder wall thickening in SHR. Specifically the mRNA levels of inflammatory factors interleukin (IL)-1α, IL-6 and TNFα were significantly higher in SHR than those in WKY rats. The SHR also had a higher number of mast cells in the suburothelium space. Type I collagen production was also significantly higher in SHR when compared to that in control rats. However, the smooth muscle content stayed the same in SHR and WKY rats. This was shown by the results that the ratio of α-smooth muscle actin (SMA) to the nuclear protein histone H3 had no difference between these two rat strains. The mRNA and protein levels of proliferating cell nuclear antigen (PCNA) also showed no change in the urinary bladder of SHR and WKY rats. Further study showed that the phosphorylation level of Akt in the urinary bladder was not changed in SHR when compared to WKY rats. In contrast, the phosphorylation level of ERK1/2 was significantly higher in SHR bladder when compared to that of WKY rats.

SIGNIFICANCE

These results suggest that inflammation and fibrosis are primary factors that may lead to urinary bladder hypertrophy in SHR.

An animal study to compare the degree of the suppressive effects on the afferent pathways of micturition between tamsulosin and sildenafil

Background

Tamsulosin, an α1-adrenoceptor antagonist, and sildenafil, a phosphodiesterase (PDE) inhibitor, are reported to improve lower urinary tract symptoms including overactive bladder (OAB). This study is aimed at investing the effects of tamsulosin and sildenafil and comparing the degree of the suppressive effects on the afferent pathways of micturition between them using an animal model of OAB, the spontaneously hypertensive rat (SHR).

Results

The cystometric parameters, the basal pressure and duration of bladder contraction, were significantly increased in the SHR group as compared with the Wistar-Kyoto (WKY) group. The intercontraction interval also significantly decreased in the SHR group. In the SHR-Tam 0.01 mg/kg group and the SHR-Sil 1 mg/kg group, however, the basal pressure and duration were significantly reduced and the intercontraction interval was significantly prolonged. Moreover, the degree of the expression of c-Fos and NGF was significantly higher in the SHR group as compared with the WKY group. But it was significantly reduced in the SHR-Tam 0.01 mg/kg group and the SHR-Sil 1 mg/kg group. Furthermore, tamsulosin had a higher degree of effect as compared with sildenafil.

Conclusions

In conclusion, α1-adrenergic receptor antagonists and PDE-5 inhibitors may have an effect in improving the voiding functions through an inhibition of the neuronal activity in the afferent pathways of micturition.

Nerve growth factor signaling following unilateral pelvic ganglionectomy in the rat ventral prostate is age dependent

Benign prostatic hyperplasia (BPH) is a serious health concern and is an underlying cause of lower urinary tract symptoms (LUTS) in many men. In affected men, LUTS/BPH is believed to result from benign proliferation of the prostate resulting in bladder outlet obstruction. Postnatal growth of the prostate is controlled via growth factor and endocrine mechanisms. However, little attention had been given to the function of the autonomic nervous system in prostate growth and differentiation. Nerve growth factor (NGF) is a prostatic mitogen that has a trophic role in autonomic sensory end organ interaction. In this study, we examine how the autonomic nervous system influences prostate growth as a function of age by quantifying NGF in the rat ventral prostate (VP) after pelvic ganglionectomy. Unilateral pelvic ganglionectomy was performed on postnatal days 30 (P30), 60 and 120 Sprague-Dawley rats in comparison to sham controls (n=39). Semiquantitative RT-PCR, Western blotting and immunohistochemical analysis for NGF were performed on denervated, intact (contralateral side) and sham control VP 7 days after surgery. Ngf RNA expression was significantly increased in the denervated and intact hyperplastic VP. Western blotting showed age-dependent increases in NGF protein at P60 in the contralateral intact VP. NGF was localized in the nerves, basal cells and columnar epithelium of the prostatic ducts. Denervation causes age-dependent increases in NGF in the VP, which is a potential mechanism by which the autonomic nervous system may regulate prostate growth and lead to BPH/LUTS.

PDE5-Is for the Treatment of Concomitant ED and LUTS/BPH

Epidemiologic data in adult men exhibit a strong relationship between erectile dysfunction (ED) and lower urinary tract symptoms suggestive of benign prostatic hyperplasia (LUTS/BPH), indicating that men affected by ED should also be investigated for LUTS/BPH and those presenting with storage or voiding LUTS should be investigated for co-morbid ED. Common pathophysiolgical mechanisms underlying both LUTS/BPH and ED, including alteration of NO/cGMP or RhoA/Rho-kinase signaling and/or vascular or neurogenic dysfunction, are potential targets for proposed phosphodiesterase type 5 inhibitors (PDE5-Is). Several randomized controlled trials and only a few reviews including all commercially available PDE5-Is demonstrated the safety and efficacy of these drugs in the improvement of erectile function and urinary symptoms, in patients affected either by ED, LUTS, or both conditions.

Evaluation of biomaterials for bladder augmentation using cystometric analyses in various rodent models

Renal function and continence of urine are critically dependent on the proper function of the urinary bladder, which stores urine at low pressure and expels it with a precisely orchestrated contraction. A number of congenital and acquired urological anomalies including posterior urethral valves, benign prostatic hyperplasia, and neurogenic bladder secondary to spina bifida/spinal cord injury can result in pathologic tissue remodeling leading to impaired compliance and reduced capacity¹. Functional or anatomical obstruction of the urinary tract is frequently associated with these conditions, and can lead to urinary incontinence and kidney damage from increased storage and voiding pressures². Surgical implantation of gastrointestinal segments to expand organ capacity and reduce intravesical pressures represents the primary surgical treatment option for these disorders when medical management fails³. However, this approach is hampered by the limitation of available donor tissue, and is associated with significant complications including chronic urinary tract infection, metabolic perturbation, urinary stone formation, and secondary malignancy^4,5.

Current research in bladder tissue engineering is heavily focused on identifying biomaterial configurations which can support regeneration of tissues at defect sites. Conventional 3-D scaffolds derived from natural and synthetic polymers such as small intestinal submucosa and poly-glycolic acid have shown some short-term success in supporting urothelial and smooth muscle regeneration as well as facilitating increased organ storage capacity in both animal models and in the clinic^6,7. However, deficiencies in scaffold mechanical integrity and biocompatibility often result in deleterious fibrosis⁸, graft contracture⁹, and calcification¹⁰, thus increasing the risk of implant failure and need for secondary surgical procedures. In addition, restoration of normal voiding characteristics utilizing standard biomaterial constructs for augmentation cystoplasty has yet to be achieved, and therefore research and development of novel matrices which can fulfill this role is needed.

In order to successfully develop and evaluate optimal biomaterials for clinical bladder augmentation, efficacy research must first be performed in standardized animal models using detailed surgical methods and functional outcome assessments. We have previously reported the use of a bladder augmentation model in mice to determine the potential of silk fibroin-based scaffolds to mediate tissue regeneration and functional voiding characteristics.^11,12 Cystometric analyses of this model have shown that variations in structural and mechanical implant properties can influence the resulting urodynamic features of the tissue engineered bladders^11,12. Positive correlations between the degree of matrix-mediated tissue regeneration determined histologically and functional compliance and capacity evaluated by cystometry were demonstrated in this model^11,12. These results therefore suggest that functional evaluations of biomaterial configurations in rodent bladder augmentation systems may be a useful format for assessing scaffold properties and establishing in vivo feasibility prior to large animal studies and clinical deployment. In the current study, we will present various surgical stages of bladder augmentation in both mice and rats using silk scaffolds and demonstrate techniques for awake and anesthetized cystometry.

Enhanced sensitivity to afferent stimulation and impact of overactive bladder therapies in the conscious, spontaneously hypertensive rat

The spontaneously hypertensive rat (SHR) has been proposed as an overactive bladder model, driven, at least partially, by alterations in bladder innervation. To assess the functional role of sensory bladder afferents we evaluated the conscious cystometric response to prostaglandin E(2) (PGE(2)) or acetic acid (AA) bladder infusion. SHR demonstrated a hypersensitivity to PGE(2) and AA, as indicated by a greater reduction in both void volume (VV) and micturition interval (MI) compared with Sprague-Dawley controls. The heightened PGE(2) and AA responses in the SHR were inhibited by capsaicin desensitization, supporting a role for bladder afferents in facilitating the hypersensitivity. Furthermore, we characterized the SHR pharmacologically using overactive bladder therapeutic agents. In the SHR, both darifenacin and oxybutynin (M(3)-selective and nonselective muscarinic antagonists, respectively) reduced micturition pressure (MP) and functional bladder capacity (VV and MI). In sharp contrast, functional bladder capacity was significantly enhanced by β(3)-adrenoceptor agonism [5-[(2R)-2-[[(2R)-2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]-1,3-benzodioxole-2,2-dicarboxylate (CL316243)], and by gabapentin, without effect on MP. These data provide the first functional evidence for hypersensitive bladder afferents in the SHR and provide a pharmacological benchmark in this model for overactive bladder therapeutics. These data also support the idea that β(3)-adrenoceptor agonism and gabapentin may provide a more effective overactive bladder therapy than muscarinic antagonism.

Intravesical PGE2 Administration in Conscious Rats as an Experimental Model of Detrusor Overactivity Observed by Simultaneous Registrations of Intravesical and Intraabdominal Pressures

PURPOSE

The urodynamic effects of intravesical PGE2 instillation on bladder function and detrusor overactivity (DO) during the filling phase were investigated in rats by measuring intraabdominal and intravesical pressures simultaneously.

MATERIALS AND METHODS

Continuous cystometry was performed inconscious, female and male Sprague- Dawley rats. We investigated pressure-, volume-, and DO-related parameters.

RESULTS

Intravesical instillation of PGE2 increased all pressure-related parameters and decreased volume-related ones, compared to the control cystometric ones. However, among the total number of intravesical pressure rises (IVPRs) above 2 cmH(2)O during the filling phase, only 33% in female rats and 38% in male rats after PGE2 instillation were identified as true DO during the filling phase.

CONCLUSIONS

Our findings suggest that the rat model with intravesical PGE2 is inappropriate for observing the effects of some drugs or mechanisms on DO, because only approximately 30% of IVPRs were confirmed as true DO. However, this model of intravesical PGE2 instillation has some advantages for the observation of changes in pressure and volume parameters rather than in DO-related ones.

Developmental aspects of bladder function

A review was conducted of the current knowledge of fetal and postnatal development of autonomic bladder function in animals. Studies of fetal and neonatal bladder development have been done in many animal species. Development of normal bladder function requires coordination of a number of different systems and processes, and continues after birth during the early neonatal period. In many neonatal animals, micturition occurs only after stimulation of a perineal-to-bladder reflex triggered when the mother licks the perineal region, and bladder distension fails to stimulate micturition. Voiding resulting from the normal bladder-to-bladder spinobulbospinal reflex activated by bladder distension develops only slowly over the first few weeks of life as synaptic connections in the sacral parasympathetic nucleus mature. The neurogenic response of bladder strips from young neonates is more sensitive to inhibition by atropine than that of strips from older animals, suggesting that there are developmental changes in the contribution of non-adrenergic, non-cholinergic transmitters to the response of the bladder smooth muscle to intramural nerve stimulation. Release of acetylcholine from cholinergic nerves and the mechanisms required to transform muscarinic receptor stimulation into efficient bladder contraction and emptying are fully developed at birth, but contractile and relaxant responses to many other agonists, such as adenosine triphosphate and noradrenaline, are developmentally regulated. Changes in calcium influx and storage may be responsible for many of these changes. Fetal detrusor is exquisitely sensitive to nitric oxide. Electrical stimulation of precontracted fetal bladder strips causes relaxation, an effect that is not seen in adult tissues, and is decreased by inhibitors of the actions of nitric oxide. Development of bladder function occurs before the onset of puberty and therefore is not normally dependent on sex hormones. However, neonatal treatment with or depletion of sex hormones can modulate bladder function. In particular, alpha-adrenergic receptor-mediated contractile responses of bladder detrusor are increased by prepubertal castration, an effect that may result from increases in the density of alpha-adrenergic receptors and/or changes in alpha-adrenergic receptor subtype expression.

Dual modulation of urinary bladder activity and urine flow by prostanoid EP3 receptors in the conscious rat

BACKGROUND AND PURPOSE

Cyclooxygenase inhibitors function to reduce levels of prostaglandin E(2) (PGE(2)) and are broadly efficacious in models of bladder overactivity. We therefore investigated a regulation of urinary bladder function in conscious rats by modulation of the EP(3) receptor for PGE(2).

EXPERIMENTAL APPROACH

The activity of the EP(3) receptor agonist GR63799X, and EP(3) receptor antagonists, CM9 and DG041, at recombinant EP(3) receptors was evaluated in vitro. In vivo, intraduodenal dosing during conscious, continuous-filling cystometry of spontaneously hypertensive rats was utilized to determine the urodynamic effect of EP(3) receptor modulation.

KEY RESULTS

GR63799X dose-dependently (0.001-1 mg x kg(-1)) reduced bladder capacity, as indicated by a reduction in both the micturition interval and volume of urine per void. In contrast, CM9 (10 and 30 mg x kg(-1)) and DG041 (30 mg x kg(-1)) enhanced bladder capacity, as indicated by significantly longer micturition intervals and larger void volumes. CM9 and DG041 inhibited the responses to GR63799X supporting the in vivo activity of these pharmacological agents at the EP(3) receptor. In addition to its effect on bladder capacity, GR63799X increased endogenous urine production. Intra-arterial infusion of saline mimicked the enhancement of urine flow observed with GR63799X, and the response was inhibited by CM9.

CONCLUSIONS AND IMPLICATIONS

These data support the EP(3) receptor as a modulator of urinary bladder activity in the conscious rat, and in addition, indicate a role for EP(3) receptor activity in regulating urine flow.

Social stress-induced bladder dysfunction: potential role of corticotropin-releasing factor

Psychological stress can impact on visceral function with pathological consequences, although the mechanisms underlying this are poorly understood. Here we demonstrate that social stress produces marked changes in bladder structure and function. Male rats were subjected to repeated (7 days) social defeat stress using the resident-intruder model. Measurement of the voiding pattern indicated that social stress produced urinary retention. Consistent with this, bladder size was increased in rats exposed to social stress. Moreover, this was negatively correlated to the latency to assume a subordinate posture, implying an association between passive behavior and bladder dysfunction. In vivo cystometry revealed distinct changes in urodynamic function in rats exposed to social stress, including increased bladder capacity, micturition volume, intermicturition interval, and the presence of non-micturition-related contractions, resembling overactive bladder. In contrast to social stress, repeated restraint (7 days) did not affect voiding, bladder weight, or urodynamics. The stress-related neuropeptide corticotropin-releasing factor (CRF) is present in spinal projections of Barrington's nucleus that regulate the micturition reflex and has an inhibitory influence in this pathway. Social stress, but not restraint, increased the number of CRF-immunoreactive neurons in Barrington's nucleus. Additionally, social stress increased CRF mRNA in Barrington's nucleus. Together, the results imply that social stress-induced CRF upregulation in Barrington's nucleus neurons results in urinary retention and, eventually, bladder dysfunction, perhaps as a visceral component of a behavioral coping response. This mechanism may underlie dysfunctional voiding in children and/or contribute to the development of stress-induced bladder disorders in adulthood.

The role of melanin-concentrating hormone-1 receptors in the voiding reflex in rats

We have used the selective melanin-concentrating hormone-1 (MCH(1)) receptor antagonist SNAP 7941 [((+)-methyl (4S)-3-{[(3-{4-[3-(acetylamino)phenyl]-1-piperidinyl}propyl) amino]carbonyl}-4-(3,4-difluorophenyl)-6-(methoxymethyl)-2-oxo-1,2,3,4-tetrahydro-5-pyrimidinecarboxylate hydrochloride)] to investigate the role of the hypothalamic neuropeptide MCH in the control of voiding in rats. Intravenous administration of SNAP 7941 (3 and 10 mg/kg i.v.) produced dose-related inhibition of rhythmic, distension-induced voiding contractions in anesthetized rats. In conscious rats in which repeated voiding cycles were evoked by continuous slow transvesicular infusion of saline, intragastric SNAP 7941 [0.03-1 mg/kg intragastrically (i.g.)] produced sustained increases in infusion capacity (maximum = 220% basal), comparable with the effects of the 5-hydroxytryptamine(1A) antagonist WAY 100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-cyclohexanecarboxamide maleate salt), and the muscarinic antagonist, oxybutynin (4-diethylaminobut-2-ynyl 2-cyclohexyl-2-hydroxy-2-phenylacetate hydrochloride). SNAP 7941 produced similar results when administered at a low dose (0.01 nmol) into the lateral ventricle (intracerebroventricular). The opposite effect was produced when MCH (20 nmol) was delivered intracerebroventricularly, resulting in a 34% decrease in apparent bladder capacity with increased urinary frequency. The effect of MCH was blocked by the prior intragastric administration of SNAP 7941 (0.1 mg/kg), but oxybutynin (1 mg/kg) was ineffective. Finally, in conscious spontaneously hypertensive rats, SNAP 7941 (0.1 mg/kg i.g.) produced a 31% reduction in micturition frequency, accompanied by a 36% increase in bladder capacity, with no effect on total volume voided over 6 h. The data indicate that MCH acts via MCH(1) receptors within the CNS to modulate the voiding reflex in rats. The striking effects of the MCH(1) antagonist SNAP 7941 to increase bladder capacity and reduce voiding frequency indicate that MCH(1) antagonists may offer a potential novel approach for treating overactive bladder syndrome.

An excitatory role for peripheral EP3 receptors in bladder afferent function

The excitatory roles of EP3 receptors at the peripheral afferent nerve innervating the rat urinary bladder have been evaluated by using the selective EP3 antagonist (2 E)-3-{1-[(2,4-dichlorophenyl)methyl]-5-fluoro-3-methyl-1 H-indol-7-yl}- N-[(4,5-dichloro-2-thienyl)sulfonyl]-2-propenamide (DG-041). The bladder rhythmic contraction model and a bladder pain model measuring the visceromotor reflex (VMR) to urinary bladder distension (UBD) have been used to evaluate DG-041 in female rats. In addition, male rats [spontaneously hypertensive rat (SHR), Wistar-Kyoto (WKY), and Sprague-Dawley (SD)] were anesthetized with pentobarbital sodium, and primary afferent fibers in the L6 dorsal root were isolated for recording the inhibitory response to UBD following intravenous injection of DG-041. Intravenous injection of DG-041 (10 mg/kg), a peripherally restricted EP3 receptor antagonist, significantly reduced the frequency of bladder rhythmic contraction and inhibited the VMR response to bladder distension. The magnitude of reduction of the VMR response was not different in the different strains of rats (SD, SHR, and WKY). Furthermore, quantitative characterization of the mechanosensitive properties of bladder afferent nerves in SHR, WKY, and SD rats did not show the SHR to be supersensitive to bladder distension. DG-041 selectively attenuated responses of mechanosensitive afferent nerves to UBD, with strong suppression on the slow-conducting, high-threshold afferent fibers, with equivalent activity in the three strains. We conclude that sensitization of afferent nerve activity was not one of the mechanisms of bladder hypersensitivity in SHR. EP3 receptors are involved in the regulation of bladder micturition and bladder nociception at the peripheral level.

Effects of the beta 3-adrenergic receptor agonist disodium 5-[(2R)-2-[[(2R)-2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]-1,3-benzodioxole-2,2-dicarboxylate (CL-316243) on bladder micturition reflex in spontaneously hypertensive rats

The present study investigated whether beta3-adrenoceptor activation acts on the bladder afferent pathway by examination of the visceromotor reflex (VMR) and pressor responses to urinary bladder distension (UBD) and whether beta3-adrenoceptor activation produces urinary bladder relaxation in hyperactive spontaneously hypertensive rats (SHRs) in comparison with their normotensive control rats [Wistar-Kyoto (WKY)]. Using the VMR responses to noxious UBD as a measure of bladder afferent signal transmission, SHRs did not present a sensitized bladder phenotype. However, reduced bladder compliance accompanied by a reduced void threshold was detected in the SHR detrusor. Furthermore, the selective beta3-adrenoceptor agonist disodium 5-[(2R)-2-[[(2R)-2-(3-chlorophenyl)-2-hydroxyethyl]-amino]propyl]-1,3-benzodioxole-2,2-dicarboxylate (CL-316243) (i.v.) failed to attenuate VMR or pressor responses to UBD in either SHRs or WKY rats, but it dose-dependently inhibited rhythmic contraction (RC) in SHRs. The minimal effective dose was 0.001 mg/kg. Using the same model in WKY rats, CL-316243 did not elicit significant inhibition of contractions in the bladder RC assay. These results suggest that SHRs represent abnormal efferent/detrusor function (detrusor overactivity) without mechanosensory afferent hypersensitivity. The beta3-adrenoceptor agonist CL-316243 acts on the detrusor muscle to increase urine storage in SHRs.

Alterations of glucose-dependent and -independent bladder smooth muscle contraction in spontaneously hypertensive and hyperlipidemic rat

Alteration of bladder contractility was examined in the spontaneously hypertensive and hyperlipidemic rat (SHHR; age, 9 months; systolic blood pressure, >150 mm Hg; plasma cholesterol, >150 mg/dl). Carbachol (CCh) induced time- and dose-dependent contractions in Sprague-Dawley (age-matched control) rats and SHHR; however, maximal levels differed significantly (13.3 +/- 2.2 and 5.4 +/- 1.9 microN/mm(2) following 10 microM CCh treatment, respectively; n = 5). This difference, which was maintained in calcium-replaced physiological salt solution (PSS), was suppressed by pretreatment with rho kinase inhibitor, 1 microM Y27632 [(R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarboxamide]; moreover, total activity of rho kinase was also reduced in SHHR bladder. Pretreatment of bladders under high-glucose (HG) conditions (22.2 mM glucose-contained PSS for 30 min) led to enhancement of CCh-induced contraction solely in control animals. Under HG conditions, both protein kinase C (PKC) activity and production of diacylglycerol (DG) derived from incorporated glucose declined in SHHR bladder; however, sustained elevation of plasma glucose level was not detected in SHHR. These results suggested that bladder contractility dysfunction in SHHR is attributable to alteration of rho kinase activity and the DG-PKC pathway. This dysfunction may occur prior to chronic hyperglycemia onset in progressive hypertension and hyperlipidemia.

Effects of doxazosin on blood flow and mRNA expression of nitric oxide synthase in the spontaneously hypertensive rat genitourinary tract

Hypertension may impact pelvic arterial blood flow resulting in reduction of nitric oxide synthase (NOS) levels. Although doxazosin, an alpha(1)-adrenoceptor antagonist, has been shown to improve erectile dysfunction as well as benign prostatic hyperplasia (BPH) and hypertension, it is not clear whether these improvements using doxazosin are primarily due to direct actions on the prostate, urinary bladder and penis, possibly via inhibition of vascular alpha(1)-adrenoceptors, or other sites of actions. Therefore, we investigated effects of doxazosin to the spontaneously hypertensive rat (SHR) on blood flow and NOS levels in the genitourinary tract. Four groups of rats were assessed: group 1, SHRs treated with doxazosin (30 mg/kg/day) for 4 weeks; group 2, SHRs treated with nifedipine (30 mg/kg/day) for 4 weeks; group 3, untreated SHRs; and group 4, untreated Wistar-Kyoto (WKY) rats. Blood flow to the ventral prostate, dorsolateral prostate, urinary bladder and penis was determined using a fluorescent microsphere infusion technique. Expression levels of nNOS and eNOS mRNAs were quantified by real-time RT-PCR using SYBR Green I. Blood flow to the ventral prostate, dorsolateral prostate, urinary bladder and penis was significantly lower in untreated SHRs than WKY rats. Treatment with doxazosin increased blood flow to each tissue studied in SHRs. RT-PCR data indicated that untreated SHRs had lower mRNA expression levels of nNOS in the bladder and penis and eNOS in the penis than WKY rats and that administration of doxazosin to the SHR caused an increase in expression levels of these genes, i.e., up-regulation of nNOS in the bladder and penis and eNOS in the penis. However, nifedipine had no significant effects on blood flow and NOS levels in the SHR genitourinary tract. Our data demonstrate that doxazosin treatment causes differential alterations in blood flow and NOS levels in the SHR genitourinary tract. These findings may provide insight into the beneficial effects of alpha(1)-adrenoceptor antagonists, on prostate, bladder and penile function, when used to treat symptoms of BPH and elevated blood pressure.

Effects of gender, age and hypertension on beta-adrenergic receptor function in rat urinary bladder

beta-Adrenoceptors mediate urinary bladder relaxation, and gender, age and hypertension have been linked to bladder dysfunction. Therefore, we have studied whether any of these factors affects the ability of beta-adrenoceptor agonists to relax rat bladder detrusor muscle in vitro. For this purpose we have compared male and female Wistar rats, young and old male Wistar rats, and male normotensive and spontaneously hypertensive rats (SHR). Comparisons were done using KCl-precontracted bladder strips (length about 15-20 mm) and the endogenous agonist noradrenaline, the synthetic non-subtype-selective agonist isoprenaline, and the prototypical beta(3)-adrenoceptor agonists BRL 37,344 and CGP 12,177. While all agonists yielded numerically weaker relaxation in female as compared to male rats (for example for noradrenaline E(max) 40+/-4% vs 53+/-6% relaxation, pEC(50) 5.41+/-0.13 vs 5.60+/-0.14), this difference reached statistical significance only for the weak partial agonist CGP 12,177. Responses to all agonists were attenuated in old as compared to young rats, largely due to a reduced maximum effect, although the difference did not reach statistical significance for isoprenaline. The maximum relaxation responses to noradrenaline and isoprenaline were significantly lower in SHR than in normotensive rats, but both strains exhibited similar responses to the partial agonist BRL 37,344. We conclude that factors associated with bladder dysfunction, such as gender, age and hypertension, can be associated with impaired beta-adrenoceptor-mediated bladder relaxation. However, these alterations are not always consistent across various agonists, and the extent of the differences can be small. Therefore, we propose that beta-adrenoceptor dysfunction may contribute to the pathophysiology of such conditions, but is unlikely to be the only or even the major factor in this regard. We speculate that beta-adrenoceptor agonists may be effective in the treatment of bladder dysfunction under all of these conditions.

Animal models in urological disease and sexual dysfunction

There are several conditions associated with dysfunction of the lower urinary tract or which result in a reduction in the ability to engage in satisfactory sexual function and result in significant bother to sufferers, partners and/or carers. This review describes some of the animal models that may be used to discover safe and effective medicines with which to treat them. While alpha adrenoceptor antagonists and 5-alpha-reductase inhibitors deliver improvement in symptom relief in benign prostatic hyperplasia sufferers, the availability of efficacious and well-tolerated medicines to treat incontinence is less well served. Stress urinary incontinence (SUI) has no approved medical therapy in the United States and overactive bladder (OAB) therapy is limited to treatment with muscarinic antagonists (anti-muscarinics). SUI and OAB are characterised by high prevalence, a growing ageing population and a strong desire from sufferers and physicians for more effective treatment options. High patient numbers with low presentation rates characterizes sexual dysfunction in men and women. The introduction of Viagra in 1998 for treating male erectile dysfunction and the success of the phosphodiesterase type 5 inhibitor class (PDE5 inhibitor) have indicated the willingness of sufferers to seek treatment when an effective alternative to injections and devices is available. The main value of preclinical models in discovering new medicines is to predict clinical outcomes. This translation can be established relatively easily in areas of medicine where there are a large number of drugs with different underlying pharmacological mechanisms in clinical usage. However, apart from, for example, the use of PDE5 inhibitors to treat male erectile dysfunction and the use of anti-muscarinics to treat OAB, this clinical information is limited. Therefore, current confidence in existing preclinical models is based on our understanding of the biochemical, physiological, pathophysiological and psychological mechanisms underlying the conditions in humans and how they are reflected in preclinical models. Confidence in both the models used and the pharmacological data generated is reinforced if different models of related aspects of the same disorder generate confirmatory data. However, these models will only be fully validated in retrospect once the pharmacological agents they have helped identify are tested in humans.

Combined use of alpha-adrenergic and muscarinic antagonists for the treatment of voiding dysfunction

PURPOSE

We provide an overview of the medical literature supporting the combined use of muscarinic and alpha-adrenergic antagonist therapy for the treatment of voiding dysfunction.

MATERIALS AND METHODS

The MEDLINE database (1966 to 2004) of the United States National Library of Medicine was searched for pertinent studies.

RESULTS

Although the mechanism of action of alpha-adrenergic antagonist therapy for voiding dysfunction has traditionally been assumed to be relaxation of the periurethral, prostatic and bladder neck smooth muscle, substantial evidence supports action at extraprostatic sites involved in micturition, including the bladder dome smooth muscle, peripheral ganglia, spinal cord and brain. Likewise the mechanism of action of anticholinergic therapy has been traditionally assumed to be inhibition of the M3 muscarinic receptor subtypes that mediate normal bladder contractions. However, M2 receptor mediates hypertrophied bladder contractions and there is evidence for an M2 component to the suprasacral control of voiding.

CONCLUSIONS

Based on the physiology of alpha-adrenergic and muscarinic receptors the inhibition of each one would be expected to be more beneficial than that of either alone because they would work on 2 components of detrusor function. Patients who would likely benefit from this combination therapy are men with lower urinary tract symptoms, women with urgency/frequency syndrome (overactive bladder), patients with uninhibited bladder contractions due to neurogenic bladder, and patients with pelvic pain and voiding symptoms, ie interstitial cystitis and chronic prostatitis/chronic pelvic pain syndrome.

CNS involvement in overactive bladder: pathophysiology and opportunities for pharmacological intervention

The pathophysiology of overactive bladder (OAB) syndrome is complex, and involves both peripheral and CNS factors. Several CNS disorders are associated with OAB, e.g. stroke, spinal cord injury, Parkinson's disease and multiple sclerosis, and in each disorder the pathophysiology of OAB can be multifactorial. Irrespective of cause or pathophysiology of OAB, antimuscarinic drugs are the first line of pharmacological treatment. However, adverse effects and limited efficacy makes alternative therapeutic principles desirable. Most alternative drugs used for the treatment of OAB have a peripheral site of action, mainly affecting efferent or afferent neurotransmission or the detrusor muscle itself. New targets for pharmacological intervention may be found in the CNS. Several CNS transmitters/transmitter systems are known to be involved in micturition control, but few drugs with a defined CNS site of action (e.g. baclofen, imipramine and duloxetine) have been used for the treatment of voiding disorders. GABA, glutamate, opioid, serotonin, noradrenaline (norepinephrine), and dopamine receptors and mechanisms are known to influence micturition, and drugs influencing these systems could potentially be developed for the treatment of OAB. Preclinical studies in different animal models have shown that modulation of normal micturition and detrusor overactivity by drugs acting within the spinal cord or supraspinally is possible. Promising results have been obtained in such models, e.g. with drugs interfering with GABA mechanisms, serotonin 5-HT1A receptors, mu-opioid receptors and alpha-adrenoreceptors. However, considering the limited predictability of existing animal models for efficacy in humans, positive proof of concept studies in humans are mandatory. Such studies are scarce and further investigations are needed.

Increased connexin43-mediated intercellular communication in a rat model of bladder overactivity in vivo

Bladder overactivity associated with outflow obstruction is a common human condition recapitulated in the female rat by narrowing the diameter of the urethra. The goal of these studies was to evaluate the role of intercellular communication through connexin43 (Cx43)-derived gap junction channels to bladder overactivity following partial urethral outflow obstruction of 3-day to 6-wk duration. Cx43 mRNA and protein expression were barely detectable by Northern or Western blots, respectively, in the detrusor layer of normal bladders, but bands were found with both techniques after 6 wk of obstruction. Linear regression analysis of the RT-PCR data revealed a statistically significant positive correlation between the duration of obstruction (again, ranging from 3-day to 6-wk duration) and Cx43 mRNA transcript levels, such that after 6 wk of obstruction, Cx43 transcript levels were approximately 15-fold greater than initial control values. When taking into account the approximately fivefold increase in bladder weight over this same time frame, the absolute amount of Cx43 mRNA in the bladder apparently increased by approximately 75-fold. In that regard, as anticipated, and consistent with previous observations, 6 wk of obstruction was also associated with a significant increase in spontaneous bladder contractions between micturitions. The amplitude of these contractions was significantly reduced by heptanol given intravesically. Furthermore, carbachol-precontracted bladder strips from obstructed animals were more sensitive to heptanol-induced relaxation (100 microM) than their unobstructed counterparts (n = 6; P < 0.01). When bladder strips were equivalently precontracted via electrical field stimulation (EFS; 20 Hz), similar heptanol-induced relaxation responses were observed. However, the tetrodotoxin-resistant portion of the EFS-induced contraction was greater in the obstructed than in the unobstructed animals, and this portion of the contractile response was more sensitive to heptanol-induced relaxation in obstructed than unobstructed bladders (n = 7; P < 0.01). Taken together, these observations indicate that partial outlet obstruction produces an overactive bladder that may be more dependent on intercellular communication through gap junctions for modulation of contractile responses than its normal counterpart.

Erectile dysfunction in spontaneously hypertensive rats: pathophysiological mechanisms

Hypertensive men have a higher prevalence of erectile dysfunction (ED) than the general population. Experimental evidence of ED in hypertensive animals is scarce. This study evaluates the erectile function of spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto rats (WKY) in vivo by the increase in intracavernosal pressure after electrical stimulation of the cavernous nerve (CN) and by isometric tension studies on corporal strips. Frequency-dependent erectile responses to CN stimulations were reduced in SHR. Phenylephrine induced lower corporal contractions in SHR although pD2 values were similar to WKY. Endothelium-dependent relaxations to ACh were impaired significantly in SHR, and indomethacin improved these relaxations in both WKY and SHR, the latter thus reaching values similar to WKY. Corporal relaxations to sodium nitroprusside were enhanced in SHR. Thus a dysfunctional alpha-adrenergic contraction of the corporal smooth muscle, an increased cyclooxygenase-dependent constrictor tone, and/or a defect in endothelium-dependent reactivity are associated with the altered erectile mechanisms in SHR. Drugs targeting endothelial dysfunction may delay the occurrence of ED as a complication of hypertension.

Bladder injection of "naked" hSlo/pcDNA3 ameliorates detrusor hyperactivity in obstructed rats in vivo

The goal of these studies was to examine the potential utility of bladder instilled K+ channel gene therapy with hSlo cDNA (i.e., the maxi-K channel) to ameliorate bladder overactivity in a rat model of partial urinary outlet obstruction. Twenty-two female Sprague-Dawley rats were subjected to partial urethral (i.e., outlet) obstruction, with 17 sham-operated control rats run in parallel. After 6 wk of obstruction, suprapubic catheters were surgically placed in the dome of the bladder in all rats. Twelve obstructed rats received bladder instillation of 100 microg of hSlo/pcDNA in 1 ml PBS during catheterization, and another 10 obstructed rats received 1 ml PBS (7 rats) or 1 ml PBS containing pcDNA only (3 rats). Two days after surgery cystometry was performed on all animals to examine the characteristics of the micturition reflex in conscious and unrestrained rats. Obstruction was associated with a three- to fourfold increase in bladder weight and alterations in virtually every micturition parameter estimate. PBS-injected obstructed rats routinely displayed spontaneous bladder contractions between micturitions. In contrast, hSlo injection eliminated the obstruction-associated bladder hyperactivity, without detectably affecting any other cystometric parameter. Presumably, expression of hSlo in rat bladder functionally antagonizes the increased contractility normally observed in obstructed animals and thereby ameliorates bladder overactivity. These initial observations indicate a potential utility of gene therapy for urinary incontinence.

Pharmacology of the lower urinary tract

The functions of the lower urinary tract, to store and periodically release urine, are dependent on the activity of smooth and striated muscles in the urinary bladder, urethra, and external urethral sphincter. This activity is in turn controlled by neural circuits in the brain, spinal cord, and peripheral ganglia. Various neurotransmitters, including acetylcholine, norepinephrine, dopamine, serotonin, excitatory and inhibitory amino acids, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in the neural regulation of the lower urinary tract. Injuries or diseases of the nervous system, as well as drugs and disorders of the peripheral organs, can produce voiding dysfunctions such as urinary frequency, urgency, and incontinence or inefficient voiding and urinary retention. This chapter will review recent advances in our understanding of the pathophysiology of voiding disorders and the targets for drug therapy.