Functional characteristics of urinary tract smooth muscles in mice lacking cGMP protein kinase type I

Impact of intravascular hemolysis on functional and molecular alterations in the urinary bladder: implications for an overactive bladder in sickle cell disease

Patients with sickle cell disease (SCD) display an overactive bladder (OAB). Intravascular hemolysis in SCD is associated with various severe SCD complications. However, no experimental studies have evaluated the effect of intravascular hemolysis on bladder function. This study aimed to assess the effects of intravascular hemolysis on the micturition process and the contractile mechanisms of the detrusor smooth muscle (DSM) in a mouse model with phenylhydrazine (PHZ)-induced hemolysis; furthermore, it aimed to investigate the role of intravascular hemolysis in the dysfunction of nitric oxide (NO) signaling and in increasing oxidative stress in the bladder. Mice underwent a void spot assay, and DSM contractions were evaluated in organ baths. The PHZ group exhibited increased urinary frequency and increased void volumes. DSM contractile responses to carbachol, KCl, α-β-methylene-ATP, and EFS were increased in the PHZ group. Protein expression of phosphorylated endothelial NO synthase (eNOS) (Ser-1177), phosphorylated neuronal NO synthase (nNOS) (Ser-1417), and phosphorylated vasodilator-stimulated phosphoprotein (VASP) (Ser-239) decreased in the bladder of the PHZ group. Protein expression of oxidative stress markers, NOX-2, 3-NT, and 4-HNE, increased in the bladder of the PHZ group. Our study shows that intravascular hemolysis promotes voiding dysfunction correlated with alterations in the NO signaling pathway in the bladder, as evidenced by reduced levels of p-eNOS (Ser-1177), nNOS (Ser-1417), and p-VASP (Ser-239). The study also showed that intravascular hemolysis increases oxidative stress in the bladder. Our study indicates that intravascular hemolysis promotes an OAB phenotype similar to those observed in patients and mice with SCD.

Low-energy shock wave therapy ameliorates ischemic-induced overactive bladder in a rat model

This study was to evaluate whether Low-energy shock wave therapy (LESW) improves ischemic-induced overactive bladder in rats and investigate its therapeutic mechanisms. Sixteen-week-old male Sprague-Dawley rats were divided into three groups: arterial injury (AI), AI with LESW (AI-SW), and control groups. LESW was irradiated in AI-SW during 20-23 weeks of age. At 24 weeks of age, conscious cystometry was performed (each n = 8). The voiding interval was shortened in AI (mean ± SEM: 5.1 ± 0.8 min) than in control (17.3 ± 3.0 min), whereas significant improvements were observed in AI-SW (14.9 ± 3.3 min). The bladder blood flow was significantly increased in AI-SW than in AI. Microarray analysis revealed higher gene expression of soluble guanylate cyclase (sGC) α1 and β1 in the bladder of AI-SW compared to AI. Protein expression of sGCα1 and sGCβ1 was higher in AI-SW and control groups than in AI. Cyclic guanosine monophosphate (cGMP) was elevated in AI-SW. As an early genetic response, vascular endothelial growth factor and CD31 were highly expressed 24 h after the first LESW. Suburothelial thinning observed in AI was restored in AI-SW. Activation of sGC-cGMP may play a therapeutic role of LESW in the functional recovery of the bladder.

Benign prostatic hyperplasia/obstruction ameliorated using a soluble guanylate cyclase activator

Benign prostatic hyperplasia (BPH) is a feature of ageing males. Up to half demonstrate bladder outlet obstruction (BOO) with associated lower urinary tract symptoms (LUTS) including bladder overactivity. Current therapies to reduce obstruction, such as α1-adrenoceptor antagonists and 5α-reductase inhibitors, are not effective in all patients. The phosphodiesterase-5 inhibitor (PDE5I) tadalafil is also approved to treat BPH and LUTS, suggesting a role for nitric oxide (NO• ), soluble guanylate cyclase (sGC), and cGMP signalling pathways. However, PDE5I refractoriness can develop for reasons including nitrergic nerve damage and decreased NO• production, or inflammation-related oxidation of the sGC haem group, normally maintained in a reduced state by the cofactor cytochrome-b5-reductase 3 (CYB5R3). sGC activators, such as cinaciguat (BAY 58-2667), have been developed to enhance sGC activity in the absence of NO• or when sGC is oxidised. Accordingly, their effects on the prostate and LUT function of aged mice were evaluated. Aged mice (≥24 months) demonstrated a functional BPH/BOO phenotype, compared with adult animals (2-12 months), with low, delayed voiding responses and elevated intravesical pressures as measured by telemetric cystometry. This was consistent with outflow tract histological and molecular data that showed urethral constriction, increased prostate weight, greater collagen deposition, and cellular hyperplasia. All changes in aged animals were attenuated by daily oral treatment with cinaciguat for 2 weeks, without effect on serum testosterone levels. Cinaciguat had only transient (1 h) cardiovascular effects with oral gavage, suggesting a positive safety profile. The benefit of cinaciguat was suggested by its reversal of an overactive cystometric profile in CYB5R3 smooth muscle knockout mice that mirrors a profile of oxidative dysfunction where PDE5I may not be effective. Thus, the aged male mouse is a suitable model for BPH-induced BOO and cinaciguat has a demonstrated ability to reduce prostate-induced obstruction and consequent effects on bladder function. © 2021 The Pathological Society of Great Britain and Ireland.

Myostatin Mutation Promotes Glycolysis by Increasing Phosphorylation of Phosphofructokinase via Activation of PDE5A-cGMP-PKG in Cattle Heart

Myostatin (MSTN) is a primary negative regulator of skeletal muscle mass and causes multiple metabolic changes. However, whether MSTN mutation affects heart morphology and physiology remains unclear. Myostatin mutation (MT) had no effect on cattle cardiac muscle in histological examination, but in biochemical assays, glycolysis increased in cattle hearts with MT. Compared with wild-type cattle, there were no differences in mRNA and protein levels of rate-limiting enzymes, but phosphofructokinase (PFK) phosphorylation increased in cattle hearts with MT. Transcriptome analysis showed that phosphodiesterase-5A (PDE5A), a target for inhibiting cGMP-PKG signaling, was downregulated. For the mechanism, chromatin immunoprecipitation qPCR showed that the SMAD2/SMAD3 complex in the canonical downstream pathway for MSTN combined with the promoter of PDE5A. The cGMP-PKG pathway was activated, and PKG increased phosphorylation of PFK in cattle hearts with MT. In addition, activation of PKG and the increase in PFK phosphorylation promoted glycolysis. Knockdown of PKG resulted in the opposite phenomena. The results indicated that MT potentiated PFK phosphorylation via the PDE5A-cGMP-PKG pathway and thereby promoted glycolysis in the heart.

The nitric oxide-cyclic guanosine monophosphate pathway inhibits the bladder ATP release in response to a physiological or pathological stimulus

The release of ATP from the epithelium of the urinary bladder (urothelium) in response to mechanical/chemical stimuli contributes to the visceral sensation in the micturition reflex. The nitric oxide (NO)-mediated induction of cyclic guanosine monophosphate (cGMP) has been detected in urothelial cells and may inhibit the micturition reflex. However, the function of the NO-cGMP pathway in the regulation of urothelial ATP release remains poorly understood in contrast to its effects on smooth muscles or primary afferent nerves. Therefore, we investigated the relevance of the NO-cGMP pathway to ATP release on the mucosal side in the present study. The administration of l-arginine (NO precursor) or NOC 12 (NO donor) significantly reduced ATP release to the mucosal side at a physiologically normal urine storage pressure (5 cmH2 O). L-NAME (NO synthase inhibitor) significantly increased the distention-induced release of ATP. The phosphodiesterase-5 inhibitor, sildenafil, which increases cGMP levels, inhibited distention-induced ATP release. Furthermore, sildenafil significantly reduced ATP release in response to the administration of lipopolysaccharide. These results suggest that the NO-cGMP pathway inhibited urothelial ATP release during the storage phase under both physiological and pathological conditions.

NO-Releasing Nanoparticles Ameliorate Detrusor Overactivity in Transgenic Sickle Cell Mice via Restored NO/ROCK Signaling

Sickle cell disease (SCD) is associated with overactive bladder (OAB). Detrusor overactivity, a component of OAB, is present in an SCD mouse, but the molecular mechanisms for this condition are not well-defined. We hypothesize that nitric oxide (NO)/ ras homolog gene family (Rho) A/Rho-associated kinase (ROCK) dysregulation is a mechanism for detrusor overactivity and that NO-releasing nanoparticles (NO-nps), a novel NO delivery system, may serve to treat this condition. Male adult SCD transgenic, combined endothelial NO synthases (eNOSs) and neuronal NOS (nNOS) gene-deficient (dNOS^-/-), and wild-type (WT) mice were used. Empty nanoparticle or NO-np was injected into the bladder, followed by cystometric studies. The expression levels of phosphorylated eNOS (Ser-1177), protein kinase B (Akt) (Ser-473), nNOS (Ser-1412), and myosin phosphatase target subunit 1 (MYPT1) (Thr-696) were assessed in the bladder. SCD and dNOS^-/- mice had a greater (P < 0.05) number of voiding and nonvoiding contractions compared with WT mice, and they were normalized by NO-np treatment. eNOS (Ser-1177) and AKT (Ser-473) phosphorylation were decreased (P < 0.05) in the bladder of SCD compared with WT mice and reversed by NO-np. Phosphorylated MYPT1, a marker of the RhoA/ROCK pathway, was increased (P < 0.05) in the bladder of SCD mice compared with WT and reversed by NO-np. nNOS phosphorylation on positive (Ser-1412) regulatory site was decreased (P < 0.05) in the bladder of SCD mice compared with WT and was not affected by NO-np. NO-nps did not affect any of the measured parameters in WT mice. In conclusion, dysregulation of NO and RhoA/ROCK pathways is associated with detrusor overactivity in SCD mice; NO-np reverses these molecular derangements in the bladder and decreases detrusor overactivity. SIGNIFICANCE STATEMENT: Voiding abnormalities commonly affect patients with sickle cell disease (SCD) but are problematic to treat. Clarification of the science for this condition in an animal model of SCD may lead to improved interventions for it. Our findings suggest that novel topical delivery of a vasorelaxant agent nitric oxide into the bladder of these mice corrects overactive bladder by improving deranged bladder physiology regulatory signaling.

Dysregulated NO/PDE5 signaling in the sickle cell mouse lower urinary tract: Reversal by oral nitrate therapy

AIMS

Nitric oxide (NO) has a critical, but not well understood, influence in the physiology of the lower urinary tract. We evaluated the effect of NO/phosphodiesterase (PDE)5 signaling in voiding dysfunction in the sickle cell disease (SCD) mouse, characterized by low NO bioavailability.

MAIN METHODS

Adult SCD (Sickle) and wild-type (WT) male mice were treated daily with sodium nitrate (10 mM) or vehicle. After 18 days, blood was obtained for nitrite measurement, urethra was collected for organ bath study, and bladder and urethra were collected for Western blot analysis of PDE5 phosphorylation (Ser-92) (activated form). Non-anesthetized mice underwent evaluation of urine volume by void spot assay. eNOS phosphorylation (Ser-1177) and nNOS phosphorylation (Ser-1412) (positive regulatory sites) were evaluated in the bladder and urethra of untreated mice.

KEY FINDINGS

Sickle mice exhibited decreased eNOS, nNOS, and PDE5 phosphorylation in the bladder and urethra, decreased plasma nitrite levels, increased relaxation of phenylephrine-contracted urethral tissue to an NO donor sodium nitroprusside, and increased total urine volume, compared with WT mice. Nitrate treatment normalized plasma nitrite levels, relaxation of urethra to sodium nitroprusside, PDE5 phosphorylation in the urethra and bladder, and urine volume in Sickle mice.

SIGNIFICANCE

Derangement in PDE5 activity associated with basally low NO bioavailability in the bladder and urethra contributes to the molecular basis for voiding abnormalities in Sickle mice. Inorganic nitrate supplementation normalized voiding in Sickle mice through mechanisms likely involving upregulation of PDE5 activity. These findings suggest that interventions targeting dysregulatory NO/PDE5 signaling may ameliorate overactive bladder in SCD.

Urinary dysfunction in transgenic sickle cell mice: model of idiopathic overactive bladder syndrome

Voiding abnormalities are common among the sickle cell disease (SCD) population, among which overactive bladder (OAB) syndrome is observed at rates as high as 39%. Although detrusor overactivity is the most common cause of OAB, its molecular pathophysiology is not well elucidated. The nitric oxide (NO) signaling pathway has been implicated in the regulation of lower genitourinary tract function. In the present study, we evaluated the role of the NO signaling pathway in voiding function of transgenic SCD mice compared with combined endothelial and neuronal NO synthase gene-deficient mice, both serving as models of NO deficiency. Mice underwent void spot assay and cystometry, and bladder and urethral specimens were studied using in vitro tissue myography. Both mouse models exhibited increased void volumes; increased nonvoiding and voiding contraction frequencies; decreased bladder compliance; increased detrusor smooth muscle contraction responses to electrical field stimulation, KCl, and carbachol; and increased urethral smooth muscle relaxation responses to sodium nitroprusside compared with WT mice. In conclusion, our comprehensive behavioral and functional study of the SCD mouse lower genitourinary tract, in correlation with that of the NO-deficient mouse, reveals NO effector actions in voiding function and suggests that NO signaling derangements are associated with an OAB phenotype. These findings may allow further study of molecular targets for the characterization and evaluation of OAB.

Erectile Dysfunction and Lower Urinary Tract Symptoms

CONTEXT

Lower urinary tract symptoms (LUTSs) and erectile dysfunction (ED) are substantial health concerns with a significant impact on the overall male quality of life.

OBJECTIVE

To evaluate the available evidence of the association between LUTSs and ED in patients with benign prostatic hyperplasia (BPH), and discuss possible clinical implications for the management of LUTS/BPH.

EVIDENCE ACQUISITION

A systematic review of the existing literature published between 1997 and June 2017 and available in the Medline, Scopus, and Web of Science databases was conducted using both the Medical Subject Heading (MeSH) and free-text protocols. The MeSH search was conducted by combining the following terms: "lower urinary tract symptoms," "LUTS," "benign prostatic hyperplasia," "BPH," "erectile dysfunction," "sexual dysfunction," "BPE," and "benign prostatic enlargement." The Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines were followed.

EVIDENCE SYNTHESIS

Several community-based studies in different geographical areas have provided strong evidence of an age-independent association between LUTSs and ED. Several biological mechanisms have been proposed to explain this association, but further research is required to better understand the molecular pathways involved. It is necessary to evaluate the possible impact of the metabolic syndrome treatment on LUTS/ED management. Considering the possible relationship between LUTSs and ED, their impact on the quality of life, and the possible adverse effects associated with LUTS medical treatment, clinicians should always evaluate ED in patients with LUTSs and take the opportunity to evaluate patients reporting ED for LUTSs.

CONCLUSIONS

Data from the peer-reviewed literature suggest the existence of an association between LUTS/BPH and ED, although their casual relationship has not been established yet. Emerging data also suggest that pathophysiological mechanisms involved in the metabolic syndrome are key factors in both disorders. Considering the association, it is also recommended that men presenting with LUTSs or ED should be evaluated for both disorders. A better understanding of the molecular pathways behind this association may also help identify new possible targets and develop novel therapeutic approaches to manage LUTSs and ED.

PATIENT SUMMARY

In this manuscript, we report on all the available evidence linking erectile dysfunction and lower urinary tract symptoms. Our findings suggest the existence of a strong relationship between these two conditions. On the basis of these findings, we recommend that clinicians always explore both conditions in male patients presenting with either of symptoms.

The Mystery of the Interstitial Cells in the Urinary Bladder

Intrinsic mechanisms to restrain smooth muscle excitability are present in the bladder, and premature contractions during filling indicate a pathological phenotype. Some investigators have proposed that c-Kit⁺ interstitial cells (ICs) are pacemakers and intermediaries in efferent and afferent neural activity, but recent findings suggest these cells have been misidentified and their functions have been misinterpreted. Cells reported to be c-Kit⁺ cells colabel with vimentin antibodies, but vimentin is not a specific marker for c-Kit⁺ cells. A recent report shows that c-Kit⁺ cells in several species coexpress mast cell tryptase, suggesting that they are likely to be mast cells. In fact, most bladder ICs labeled with vimentin antibodies coexpress platelet-derived growth factor receptor α (PDGFRα). Rather than an excitatory phenotype, PDGFRα⁺ cells convey inhibitory regulation in the detrusor, and inhibitory mechanisms are activated by purines and stretch. PDGFRα⁺ cells restrain premature development of contractions during bladder filling, and overactive behavior develops when the inhibitory pathways in these cells are blocked. PDGFRα⁺ cells are also a prominent cell type in the submucosa and lamina propria, but little is known about their function in these locations. Effective pharmacological manipulation of bladder ICs depends on proper identification and further study of the pathways in these cells that affect bladder functions.

Crucial roles of nitric oxide synthases in β-adrenoceptor-mediated bladder relaxation in mice

The specific roles of nitric oxide (NO) synthases (NOSs) in bladder smooth muscle remain to be elucidated. We examined the roles of NOSs in β-adrenoceptor (AR)-mediated bladder relaxation. Male mice (C57BL6) deficient of neuronal NOS [nNOS-knockout (KO)], endothelial NOS (eNOS-KO), neuronal/endothelial NOS (n/eNOS-KO), neuronal/endothelial/inducible NOS (n/e/iNOS-KO), and their controls [wild-type (WT)] were used. Immunohistochemical analysis was performed in the bladder. Then the responses to relaxing agents and the effects of several inhibitors on the relaxing responses were examined in bladder strips precontracted with carbachol. Immunofluorescence staining showed expressions of nNOS and eNOS in the urothelium and smooth muscle of the bladder. Isoproterenol-induced relaxations were significantly reduced in nNOS-KO mice and were further reduced in n/eNOS-KO and n/e/iNOS-KO mice compared with WT mice. The relaxation in n/e/iNOS-KO mice was almost the same as in n/eNOS-KO mice. Inhibition of Ca2+-activated K+ (KCa) channel with charybdotoxin and apamin abolished isoproterenol-induced bladder relaxation in WT mice. Moreover, direct activation of KCa channel with NS1619 caused comparable extent of relaxations among WT, nNOS-KO, and n/eNOS-KO mice. In contrast, NONOate (a NO donor) or hydrogen peroxide (H2O2) (another possible relaxing factor from eNOS) caused minimal relaxations, and catalase (H2O2 scavenger) had no inhibitory effects on isoproterenol-induced relaxations. These results indicate that both nNOS and eNOS are substantially involved in β-AR-mediated bladder relaxations in a NO- or H2O2-independent manner through activation of KCa channels.

Expression and distribution of phosphodiesterase isoenzymes in the human male urethra

OBJECTIVE

To investigate the expression and distribution of phosphodiesterase (PDE) isoenzymes PDE1A, PDE2A, PDE4A, PDE4B, and PDE5A in human urethral tissue.

METHODS

Specimens of penile urethra were obtained from male subjects who had undergone male-to-female sex reassignment surgery. Using immunohistochemistry (immunofluorescence), the occurrence of PDE1A, PDE2A, PDE4A, PDE4B, and PDE5A, the neuronal nitric oxide synthase, calcitonin gene-related peptide, and vasoactive intestinal polypeptide was examined in urethral sections. Cytosolic supernatants prepared from isolated human urethral tissue were subjected to Western blot analysis using specific anti-PDE antibodies.

RESULTS

Immunosignals specific for PDE1A, 4A, 4B, and 5A were observed in the urethral smooth musculature. The smooth muscle bundles were seen innervated by slender nerve fibers, characterized by the expression of the neuronal nitric oxide synthase, calcitonin gene-related peptide, and vasoactive intestinal polypeptide. The expression of the PDE isoenzymes mentioned was confirmed by Western blotting.

CONCLUSION

The results provide evidence for a significance of both the cyclic adenosine monophosphate and cyclic guanosine monophosphate signaling in the control of human urethral smooth muscle. The selective inhibition of PDE isoenzymes might represent a pharmacologic option to influence the function of smooth musculature in the human outflow region.

Changes in nerve-mediated contractility of the lower urinary tract in a mouse model of premature ageing

BACKGROUND AND PURPOSE

A high incidence of lower urinary tract disorders is associated with ageing. In the senescent-accelerated prone (SAMP8) mouse strain and the senescent-accelerated resistant (SAMR1) strain, we compared smooth muscle contractility in responses to intrinsic neurotransmitters, both in the bladder and urethra.

EXPERIMENTAL APPROACH

We analysed micturition frequency, the changes in muscle tension induced by electrical field stimulation or agonist administration, the density of nerves (adrenergic, cholinergic and nitrergic) and interstitial cells (ICs), as well as cGMP accumulation in bladder and urethral preparations.

KEY RESULTS

Senescent mice of the SAMP8 strain displayed increased micturition frequency and excitatory contractility of neurogenic origin in the bladder. While cholinergic nerve density remained unchanged, there was a mild sensitization to ACh in male mice. Potentiation in the detrusor may be also provoked by the stronger contribution of ATP, together with reduced adrenergic innervation in males and COX-derived prostanoid production in females. The greater excitatory contractility in the urethra was probably due to the sensitization to noradrenaline, in conjunction with attenuated nitrergic relaxation. There were also fewer neuronal NOS immunoreactive (ir) nerves and vimentin-positive ICs, although the sildenafil- and diethylamine-NONOate-induced relaxations and cGMP-ir remained unchanged.

CONCLUSIONS AND IMPLICATIONS

Premature senescent mice exhibit bladder and urethral hyperexcitability, coupled with reduced urethral relaxation of neurogenic origin, which could model the impaired urinary function in elderly humans. We propose that senescence-accelerated mice provide a useful tool to analyse the basic mechanisms of age-related changes in bladder and urethral function.

Interstitial cells: regulators of smooth muscle function

Smooth muscles are complex tissues containing a variety of cells in addition to muscle cells. Interstitial cells of mesenchymal origin interact with and form electrical connectivity with smooth muscle cells in many organs, and these cells provide important regulatory functions. For example, in the gastrointestinal tract, interstitial cells of Cajal (ICC) and PDGFRα(+) cells have been described, in detail, and represent distinct classes of cells with unique ultrastructure, molecular phenotypes, and functions. Smooth muscle cells are electrically coupled to ICC and PDGFRα(+) cells, forming an integrated unit called the SIP syncytium. SIP cells express a variety of receptors and ion channels, and conductance changes in any type of SIP cell affect the excitability and responses of the syncytium. SIP cells are known to provide pacemaker activity, propagation pathways for slow waves, transduction of inputs from motor neurons, and mechanosensitivity. Loss of interstitial cells has been associated with motor disorders of the gut. Interstitial cells are also found in a variety of other smooth muscles; however, in most cases, the physiological and pathophysiological roles for these cells have not been clearly defined. This review describes structural, functional, and molecular features of interstitial cells and discusses their contributions in determining the behaviors of smooth muscle tissues.

Correlation of cellular expression with function of NO-sensitive guanylyl cyclase in the murine lower urinary tract

The action of nitric oxide (NO) to stimulate NO-sensitive guanylyl cyclase (NO-GC), followed by production of cGMP, and eventually to cause smooth muscle relaxation is well known. In the lower urinary tract (LUT), in contrast to the cardiovascular system and the gastrointestinal tract, specific localization in combination with function of NO-GC has not been investigated to date. Consequently, little is known about the mechanisms regulating relaxation of the lower urinary tract in general and the role of NO-GC-expressing cells in particular. To study the distribution and function of NO-GC in the murine lower urinary tract, we used internal urethral sphincter and bladder detrusor from global (GCKO) and smooth muscle cell-specific (SM-GCKO) NO-GC knock-out mice for immunohistochemical analyses and organ bath experiments. In urethral sphincter, NO-GC-positive immunofluorescence was confined to smooth muscle cells (SMCs). Deletion of NO-GC in SMCs abolished NO-induced relaxation. In bladder detrusor, exposure to NO did not cause relaxation although immunohistochemistry uncovered the existence of NO-GC in the tissue. In contrast to the urethral sphincter, expression of NO-GC in bladder detrusor was limited to platelet-derived growth factor receptor α (PDGFRα)-positive interstitial cells. In conclusion, NO-GC found in SMCs of the urethral sphincter mediates NO-induced relaxation; bladder detrusor is unique as NO-GC is not expressed in SMCs and, thus, NO does not induce relaxation. Nevertheless, NO-GC expression was found in PDGFRα-positive interstitial cells of the murine bladder with an as yet unknown function. Further investigation is needed to clarify the role of NO-GC in the detrusor.

Transcriptional and post-transcriptional regulation of cGMP-dependent protein kinase (PKG-I): pathophysiological significance

The ability of the endothelium to produce nitric oxide, which induces generation of cyclic guanosine monophosphate (cGMP) that activates cGMP-dependent protein kinase (PKG-I), in vascular smooth muscle cells (VSMCs), is essential for the maintenance of vascular homeostasis. Yet, disturbance of this nitric oxide/cGMP/PKG-I pathway has been shown to play an important role in many cardiovascular diseases. In the last two decades, in vitro and in vivo models of vascular injury have shown that PKG-I is suppressed following nitric oxide, cGMP, cytokine, and growth factor stimulation. The molecular basis for these changes in PKG-I expression is still poorly understood, and they are likely to be mediated by a number of processes, including changes in gene transcription, mRNA stability, protein synthesis, or protein degradation. Emerging studies have begun to define mechanisms responsible for changes in PKG-I expression and have identified cis- and trans-acting regulatory elements, with a plausible role being attributed to post-translational control of PKG-I protein levels. This review will focus mainly on recent advances in understanding of the regulation of PKG-I expression in VSMCs, with an emphasis on the physiological and pathological significance of PKG-I down-regulation in VSMCs in certain circumstances.

Protein kinase G-I deficiency induces pulmonary hypertension through Rho A/Rho kinase activation

Protein kinase G (PKG) plays an important role in the regulation of vascular smooth cell contractility and is a critical mediator of nitric oxide signaling, which regulates cardiovascular homeostasis. PKG-I-knockout (Prkg1(-/-)) mice exhibit impaired nitric oxide/cGMP-dependent vasorelaxation and systemic hypertension. However, it remains unknown whether PKG-I deficiency induces pulmonary hypertension. In this study, we characterized the hypertensive pulmonary phenotypes in Prkg1(-/-) mice and delineated the underlying molecular basis. We observed a significant increase in right ventricular systolic pressure in Prkg1(-/-) mice in the absence of systemic hypertension and left-sided heart dysfunction. In addition, we observed marked muscularization of distal pulmonary vessels in Prkg1(-/-) mice. Microangiography revealed impaired integrity of the pulmonary vasculature in Prkg1(-/-) mice. Mechanistically, PKG-I-mediated phosphorylation of Rho A Ser188 was markedly decreased, and the resultant Rho A activation was significantly increased in Prkg1(-/-) lung tissues, which resulted in Rho kinase activation. The i.t. administration of fasudil, a Rho kinase inhibitor, reversed the hypertensive pulmonary phenotype in Prkg1(-/-) mice. Taken together, these data show that PKG-I deficiency induces pulmonary hypertension through Rho A/Rho kinase activation-mediated vasoconstriction and pulmonary vascular remodeling.

Neuronal-derived nitric oxide modulates the activity of mouse detrusor smooth muscle

AIMS

We investigated the roles of neuronal-derived nitric oxide (NO) in the modulation of spontaneous activity of mouse detrusor smooth muscle.

METHODS

Detrusor smooth muscle strips were isolated from nNOS gene knock-out (nNOS(-/-) ) mice and their wild type siblings (nNOS(+/+) ). The properties of smooth muscle cells were assessed using intracellular electrophysiology and Ca(2+) imaging by laser-scanning confocal microscopy. The effects of an nNOS inhibitor, 7-nitro indazole (7-NI) on electrically evoked contractility were assessed using nNOS(+/+) mouse detrusor strips.

RESULTS

In spontaneously active cells, the frequency of spontaneous action potentials (sAPs) and whole cell Ca(2+) flashes in nNOS(-/-) preparations was lower than that in the nNOS(+/+) preparations. The frequency of sAPs was enhanced by a nitric oxide donor, diethylamine NONOate sodium salt (NONOate; 100 µM), both when used alone and when the cGMP pathway was blocked by 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one (ODQ, 10 µM). 7-NI (100 µM) significantly suppressed the electrically evoked contraction of mouse detrusor strips.

CONCLUSIONS

We suggest that neuronal-derived NO facilitates the generation of spontaneous activity via a cGMP-independent pathway, and consequently enhances the evoked contraction of detrusor. Dysregulation of nNOS containing nerves may underlie bladder pathologies.

Bladder mechanoreceptor changes after artificial bladder outlet obstruction in the anesthetized rat

AIMS

Experimental animal models of bladder outlet obstruction (BOO) have reproduced several features of BOO in man, i.e., detrusor hypertrophy, instability, frequency, and residual urine. This study was focused on the mechanisms underlying the development of residual urine in patient with benign prostatic hyperplasia (BPH) by examining changes in tension sensitivity of bladder mechanoreceptors in rat model.

METHODS

Female adult Sprague-Dawley rats including 12 BOO and 17 sham operated rats were used in this study. Cystometrograms together with the bladder afferent activity were recorded. Tension sensitivity of the afferents was determined by plotting the normalized afferent response against the contraction evoked bladder pressure at different volumes. Degree of obstruction was assessed by the wet weight of the bladder at the end of the experiment.

RESULTS

The bladder weight, maximal bladder capacity, micturition threshold volume, peak contraction force, and volume at peak contraction force were all significantly increased in obstructed animals. The threshold volume for afferent activation was increased (mean 0.60 ml compared to 0.15 ml in controls; P < 0.001), positively correlated with the bladder weight (r = 0.74). The tension sensitivity of the bladder mechanoreceptors and the slope of their normalized pressure-response functions were significantly lower at the comparable volumes in the obstructed animals.

CONCLUSIONS

Rats with BOO had bladder mechanoreceptors with higher threshold volumes and lower tension sensitivity. Such changes would result in a weaker afferent drive of the micturition reflex. Similar changes may contribute to the development of residual urine and retention in patients with BOO.

Rodent models for urodynamic investigation

Rodents, most commonly rats, mice, and guinea pigs are widely used to investigate urinary storage and voiding functions, both in normal animals and in models of disease. An often used methodology is cystometry. Micturitions in rodents and humans differ significantly and this must be considered when cystometry is used to interpret voiding in rodent models. Cystometry in humans requires active participation of the investigated patient (subject), and this can for obvious reasons not be achieved in the animals. Cystometric parameters in rodents are often poorly defined and do not correspond to those used in humans. This means that it is important that the terminology used for description of what is measured should be defined, and that the specific terminology used in human cystometry should be avoided. Available disease models in rodents have limited translational value, but despite many limitations, rodent cystometry may give important information on bladder physiology and pharmacology. The present review discusses the principles of urodynamics in rodents, techniques, and terminology, as well as some commonly used disease models, and their translational value.

Characterization of the urinary bladder dysfunction in renovascular hypertensive rats

AIMS

Association between arterial hypertension and urinary bladder dysfunction has been reported in humans and spontaneously hypertensive rats. However, no study exists evaluating the bladder dysfunction in conditions of renovascular hypertension. The purpose of this study was to characterize the bladder dysfunction in two kidney-one clip (2K-1C) hypertensive rats.

METHODS

A silver clip was placed around the renal artery of male Wistar rats. After 8 weeks, cystometric study, concentration-response curves to contractile and relaxant agents, frequency-dependent contractions, histomorphometry, muscarinic M(2) /M(3) mRNA expression and cyclic AMP measurements were performed.

RESULTS

2K-1C rats showed enhanced bladder volume, wall thickness and smooth muscle density. 2K-1C rats also exhibited increases in bladder capacity and non-void contractions, and decreases in the inter-contraction intervals. In isolated detrusor smooth muscle (DSM), contractions to carbachol and electrical-field stimulation (EFS) were significantly greater in 2K-1C rats. The Rho-kinase inhibitor Y27632 (10 µM) significantly reduced the carbachol-induced contractions in SHAM and 2K-1C rats, but DSM remained overactive in 2K-1C rats in presence of Y27632. Concentration-dependent contractions to the P2X receptor agonist α,β-methylene ATP, KCl and extracellular Ca(2+) did not change between SHAM and 2K-1C groups. In 2K-1C rats, isoproterenol, metaproterenol and BRL 37-344 (non-selective, β(2) - and β(3) -selective adrenoceptor agonists, respectively) produced significantly lower relaxations and decreased cAMP levels, whereas relaxant responses to sodium nitroprusside and BAY 41-2272 remained unchanged. Muscarinic M(3) mRNA expression receptors were higher in 2K-1C group.

CONCLUSIONS

Renovascular hypertensive rats exhibit bladder dysfunction that involves tissue remodeling and enhanced muscarinic M(3) -mediated contractions associated with reduced β-adrenoceptor-mediated signal transduction.

Cyclic GMP signaling in rat urinary bladder, prostate, and epididymis: tissue-specific changes with aging and in response to Leydig cell depletion

Aging of the male reproductive system leads to changes in endocrine signaling and is frequently associated with the emergence of prostate hyperplasia and bladder dysfunctions. Recent reports highlight prostate and bladder as promising targets for therapeutic interventions with inhibitors of the cyclic GMP (cGMP)-degrading phosphodiesterase 5 (PDE5). However, the cGMP signaling system in these organs is as yet poorly characterized, and the possibility of age-related alterations has not been addressed. This study investigates key proteins of cGMP pathways in bladder, prostate, and epididymis of young (3 months) and old (23-24 months) Wistar rats. Local differences in the abundance of PDE5, soluble guanylyl cyclase (sGC) and particulate guanylyl cyclases (GC-A, GC-B), endothelial nitric oxide synthase, and cGMP-dependent protein kinase I (PRKG1 (cGKI)) revealed pronounced tissue-specific peculiarities. Although cGMP-generating enzymes were not affected by age in all organs, we recognized age-related decreases of PDE5 expression in bladder and a selective diminishment of membrane-associated PRKG1 in epididymis. In disagreement with published data, all cGMP pathway proteins including PDE5 are poorly expressed in prostate. However, prostatic PRKG1 expression increases with aging. Androgen withdrawal during temporary Leydig cell elimination induced a massive (>12-fold) upregulation of PRKG1 in prostate but not in other (penis and epididymis) androgen-dependent organs. These findings identify PRKG1 as a key androgen-sensitive signaling protein in prostate of possible importance for growth regulation. The elucidated effects may have significance for age-associated pathologies in the male lower-urinary tract.

Tadalafil for the treatment of lower urinary tract symptoms secondary to benign prostatic hyperplasia: pathophysiology and mechanism(s) of action

BACKGROUND

The PDE5 inhibitor tadalafil is investigation for the treatment of lower urinary tract symptoms (LUTS) in men with benign prostatic hyperplasia (BPH). Several clinical studies of tadalafil and other PDE5 inhibitors have reported significant symptom reduction but limited urinary flow rate improvement. This manuscript reviews the published literature describing the pathophysiology of male LUTS, with an emphasis on mechanisms that may be modulated or improved by phosphodiesterase type 5 (PDE5) inhibition.

METHODS

Literature (through March 2010) was obtained via Medline searches and from the individual reviewers files. Articles were selected for review based on describing in vitro, preclinical, or clinical studies of pathological processes contributing to LUTS, or possible effects of PDE5 inhibition in the lower urinary tract.

RESULTS

Major mechanisms contributing to LUTS include: reduced nitric oxide/cyclic guanosine monophosphate signaling; increased RhoA kinase pathway activity; autonomic overactivity; increased bladder afferent activity; and pelvic ischemia. Tadalafil and other PDE5 inhibitors have demonstrated beneficial effects on smooth muscle relaxation, smooth muscle and endothelial cell proliferation, nerve activity, and tissue perfusion that may impact LUTS in men.

CONCLUSIONS

The pathophysiology of male LUTS is complex and not completely understood. LUTS may occur independently of BPH or secondary to BPH but in both cases involve obstructive or irritative mechanisms with substantial pathophysiological overlap. While the precise mechanism remains unclear, inhibition of PDE5 seems to have an effect on several pathways that may impact LUTS.

Cyclic nucleotide metabolism including nitric oxide and phosphodiesterase-related targets in the lower urinary tract

The clinical data on the use of the orally active phosphodiesterase (PDE) type 5 inhibitors sildenafil (VIAGRA™), vardenafil (LEVITRA™), and tadalafil (CIALIS™) for the treatment of male erectile dysfunction have boosted research activities on the physiology and pharmacology of the organs of the lower urinary tract (LUT). This includes both intracellular signal transduction in the prostate, urinary bladder (detrusor), and urethra, as well as central brain and spinal cord pathways controlling the function of the LUT. Such efforts provided the basis for the development of new therapeutic modalities into the management of dysfunctions/ syndromes of the LUT, some of which are already offered to the patients. The pharmacological treatment of the overactive bladder and the so-called benign prostatic syndrome, including LUT symptomatology and bladder outlet obstruction secondary to benign prostatic enlargement, has primarily focused on selective, orally available drugs acting by influencing intracellular regulatory mechanisms. These agents are regarded efficacious, have a fast onset of drug action in the target tissue and an improved effect-to-side-effect ratio. Better understanding of the functional significance of proteins related to cyclic nucleotide-dependent pathways, such as nitric oxide synthase, cytosolic and membrane-bound guanylyl cyclases, PDE isoenzymes and cyclic AMP- and cyclic GMP-binding protein kinases, the relative distribution in tissues of the LUT, and the consequences for urogenital function, seems to be of particular interest in order to identify new or more selective pharmacological approaches to manage disorders of the LUT. The present review focuses on cyclic nucleotide-related targets involved in the control of the function of the bladder, prostate, and urethra and the significance of those proteins in the process of evolving new pharmacological options for the treatment of LUT symptoms secondary to benign prostatic hyperplasia as well as dysfunctions of the storage and voiding capability of the urinary bladder.

Administration of BAY 41-2272 prevents bladder dysfunction in nitric-oxide deficient rats

OBJECTIVE

to evaluate the protective effects of BAY 41-2272, a soluble guanylate cyclase activator, on changes in cystometric parameters in rats deficient in nitric oxide (NO).

METHODS

Rats were divided into the following groups: (a) control; (b) DMSO; (c) L-NAME; (d) BAY 41-2272 alone; (e) L-NAME + BAY 41-2272. The NO synthase blocker L-NAME (20 mg/rat/day) was given in drinking water concomitantly or not with BAY 41-2272 (10 mg/kg/day, given by gavage).

RESULTS

Chronic L-NAME treatment markedly increased the mean arterial blood pressure, and co-treatment with BAY 41-2272 nearly reversed L-NAME-induced rise on mean arterial blood pressure. Non-void contractions were significantly increased in L-NAME group (0.90 ± 0.1 number/minute) compared with either DMSO or control group (0.49 ± 0.1 number/minute), which were prevented by co-treatment with BAY 41-2272 (0.56 ± 025 number/minute; p < 0.05). The threshold and peak pressure increased by 70 and 44%, respectively, after chronic L-NAME treatment, while co-treatment with BAY 41-2272 largely attenuated both effects (27 and 22% increase, respectively). The frequency of micturition cycles decreased by about of 50% in L-NAME-treated rats compared with control animals, and co-treatment with BAY 41-2272 normalized this parameter.

CONCLUSIONS

Our data show that long-term oral administration of BAY 41-2272 counteracts the bladder dysfunction seen in NO-deficient rats, indicating that restoration of the NO-cGMP pathway by this compound may be of beneficial value to treat bladder symptoms.

Evaluation of the relaxant effect of the nitric oxide-independent soluble guanylyl cyclase stimulator BAY 41-2272 in isolated detrusor smooth muscle

The nitric oxide (NO)-independent soluble guanylyl cyclase stimulator stimulator BAY 41-2272 was reported to produce relaxant response in different types of smooth muscle. However no study was carried out to investigate the effects of BAY 412282 in detrusor smooth muscle. Thus, this study aimed to evaluate the relaxant effects of BAY 41-2272, in isolated mouse, rat and rabbit detrusor smooth muscle. Mouse, rat and rabbit were anesthetized, and urinary bladder removed. Detrusor smooth muscle was transferred to 10-mL organ baths containing oxygenated and warmed Krebs-Henseleit solution. Tissues were connected to force-displacement transducers and changes in isometric force were recorded. BAY 41-2272 (0.001-100 microM) produced concentration-dependent detrusor smooth muscle relaxations in mouse, rat and rabbit with maximal responses of 61.3+/-6.6%, 95.1+/-9.9% and 91.7+/-5.9%, respectively. Sodium nitroprusside and glyceryl trinitrate, as well as 8-bromo-cGMP also produced detrusor relaxations, but to a much lesser extent than BAY 41-2272. The NO synthesis inhibitor L-NAME and the phosphodiesterase-5 inhibitor sildenafil had no effect in BAY 41-2272-induced responses. However, the soluble guanylyl cyclase inhibitor ODQ significantly reduced BAY 41-2272-induced relaxations. BAY 41-2272 increased the bladder cGMP levels by about of 14- and 20-fold for 10 and 100 microM, respectively, which were markedly reduced by ODQ. The cAMP levels were unaffected by BAY 41-2272. Moreover, BAY 41-2272 significantly reduced the contractile responses to extracellular Ca(2+) in an ODQ-insensitive manner. In conclusion, rabbit detrusor smooth muscle relaxations by BAY 41-2272 involve mainly cGMP production, but an additional mechanism involving Ca(2+) influx blockade independently of cGMP production appears to be involved.

Detrusor myocyte activity and afferent signaling

AIMS

To discuss (1) mechanisms involved in the generation and control of myocyte contractions and consequent afferent nerve activity and (2) these mechanisms as targets for drugs aimed for treatment of overactive bladder (OAB) symptoms and detrusor overactivity (DO).

METHODS

Literature review of myocyte activation, bladder afferent nerves, mediators in the bladder, and translational aspects of the findings.

RESULTS

During bladder filling, there is normally no parasympathetic outflow from the spinal cord. Despite this, the bladder develops tone during filling and also exhibits non-synchronized local contractions and relaxations that are caused by a basal myogenic mechanical activity that may be reinforced by release of, for example, acetylcholine from non-neuronal and/or neuronal sources or local mediators, such as prostaglandins and endothelins. It is suggested that these spontaneous contractions are able to generate activity in afferent nerves ("afferent noise") that may contribute to DO and OAB.

CONCLUSIONS

Spontaneous bladder myocyte contractions and factors that are able to modulate them, as well as the consequent afferent nerve activity, may be targets for drugs meant for treatment of OAB/DO.

Bladder dysfunction in a new mutant mouse model with increased superoxide--lack of nitric oxide?

PURPOSE

Nitric oxide mediates urethral smooth muscle relaxation and may also be involved in detrusor activity control. Mice with mutation in the Immp2l gene have high superoxide ion levels and a consequent decrease in the bioavailable amount of nitric oxide. We studied bladder function in this mouse model.

MATERIAL AND METHODS

Young male mutants at ages 4 to 6 months, old female mutants at age 18 months and healthy WT age matched controls were used. The detrusor contractile response to carbachol and electrical field stimulation was tested in isolated detrusor strips in organ baths. In vivo bladder function was evaluated by cystometry in conscious animals.

RESULTS

Young male mutants had significantly lower micturition and higher post-void residual volume than WT controls. They had pronounced voiding difficulty and strained when initiating micturition. Detrusor contractile responses to carbachol and electrical field stimulation were similar in mutant and WT mice. Old female mutant mice had lower bladder capacity and micturition volume, and higher micturition frequency and bladder-to-body weight ratio than WT controls. In the in vitro study detrusor strips from mutants showed a lower maximum response to carbachol.

CONCLUSIONS

Mice with mutation in the Immp2l gene have bladder dysfunction, mainly characterized by emptying abnormalities in young males and increased detrusor activity in old females. Detrusor function was preserved in young males and impaired in old females. These animals are a natural model of oxidative stress with low bioavailable nitric oxide. Thus, they are interesting tools in which to evaluate the role of these conditions on bladder dysfunction.

Presence of cyclic nucleotide-gated channels in the rat urethra and their involvement in nerve-mediated nitrergic relaxation

We have addressed the distribution of cGMP-gated channels (CNG) in the rat urethra for the first time, as well as their putative role in mediating of the relaxation elicited by electrical field stimulation of nitrergic nerves. Functional studies have shown that specifically blocking CNG with L-cis-diltiazem leads to the rapid inhibition of urethral relaxation induced either by nitric oxide (NO) released by the nerves or by soluble guanylate cyclase activated with YC-1. By contrast, nerve-mediated noradrenergic contractions were only slowly and mildly reduced by L-cis-diltiazem. This effect was mimicked by lower concentrations of the D-diltiazem isomer, probably due to the nonspecific inhibition of voltage-dependent calcium channels. However, D-diltiazem did not affect relaxation responses. The expression of heteromeric retinal-like CNGA1 channels was demonstrated by conventional PCR on mRNA from the rat urethra. These channels were located in a subpopulation of intramuscular interstitial cells of Cajal (ICC) as well as in smooth muscle cells, although they were less abundant in the latter. CNG channels could not be visualized in any nervous structure within the urethral wall, in agreement with the emerging view that a subset of ICC serves as a target for NO. These channels could provide a suitable ionic mechanism to associate the changes in cytosolic calcium with the activation of the nitric NO-cGMP pathway and relaxation although the precise mechanisms involved remain to be elucidated.

Vardenafil-induced relaxation and cyclic nucleotide levels in normal and obstructed rat urinary bladder

OBJECTIVE

To study the effects of the phosphodiesterase-5 inhibitor, vardenafil, on contraction and cyclic nucleotide levels in isolated detrusor preparations with and without mucosa, from control rats and rats with partial urethral obstruction (PUO) and intact mucosa.

MATERIALS AND METHODS

Female Sprague-Dawley rats were divided into groups subjected to PUO for 14 days (six), and sham-operated control rats (12). Detrusor preparations were mounted in organ baths and effects of increasing concentrations of vardenafil (1 nm to 100 microm) assessed on carbachol-activated (1 microm) preparations, and on contractions induced by transmural activation of nerves (electrical field stimulation, EFS). Levels of cGMP and cAMP were determined using radioimmunoassays.

RESULTS

Vardenafil caused concentration-dependent relaxations of carbachol-contracted detrusor, the mean (sd) of which at 100 microm was 91 (4)% in control and 100% in PUO rats. The -log 50% inhibitory concentration (IC(50)) was 4.41 (0.08) and 4.73 (0.05) (P < 0.01), respectively. Removing the mucosa increased the relaxant effect of vardenafil at 1-10 microm (P < 0.05) although -log IC(50) values were unaffected compared to the control. The cGMP levels ( pmol/mg protein) in control preparations increased from 2.5 (0.6) to 5.0 (0.8), and from 1.4 (0.2) to 7.2 (1.3) in obstructed bladders. In mucosa-denuded preparations the cGMP content increased from 0.6 (0.1) to 1.6 (0.4) in response to vardenafil. In control rats, the levels of cAMP increased from 12.8 (2.5) to 18.9 (0.9) (P < 0.05) after vardenafil. In mucosa-denuded preparations the cAMP levels after vardenafil increased from 16.5 (2.11) to 37.8 (3.4) (P < 0.01). In PUO bladders, the tissue content of cAMP increased from 12.6 (2.4) to 20.6 (3.4) (P < 0.01). Vardenafil concentration-dependently inhibited nerve-induced contractions in all groups studied. At 100 microm 19 (3)% of the control contraction remained, vs 8 (1)% for preparations from obstructed rats, and 11 (4)% in mucosa-denuded preparations.

CONCLUSION

In normal rats, vardenafil relaxed carbachol- and inhibited EFS-induced contractions of detrusor preparations with and without urothelium, and in PUO rats with urothelium. Relaxations were accompanied by increases in both cAMP and cGMP content. It is proposed that vardenafil-induced relaxation of rat detrusor, also in obstructed and mucosa-denuded preparations, is mediated via cAMP.

Activation of the nitric oxide-cGMP pathway reduces phasic contractions in neonatal rat bladder strips via protein kinase G

Nitric oxide (NO), a neurotransmitter in the lower urinary tract, stimulates soluble guanylyl cyclase (sGC) and in turn cGMP-dependent protein kinase G (PKG) to modulate a number of downstream targets. NO donors reduce bladder hyperactivity in some pathological models but do not affect normal bladder activity in the adult rat. In this study, the NO donor S-nitroso-N-acetyl-DL-penicillamine (SNAP; 100 microM) decreased the amplitude and frequency of spontaneous and carbachol-enhanced contractions in neonatal rat bladder strips, which are intrinsically hyperactive. This effect was blocked by inhibition of sGC and mimicked by application of a membrane-permeable cGMP analog (8-bromo-cGMP, 100 microM). Inhibition of PKG prevented or reversed the inhibitory effects of 8-bromo-cGMP. A portion of the SNAP-mediated inhibition was also dependent upon PKG; however, a short-lasting, sGC-dependent inhibitory effect of SNAP was still present after PKG inhibition. Inhibition of NO synthase with L-NAME (100 microM) did not change the amplitude or frequency of contractions. However, inhibition of endogenous phosphodiesterase (PDE)-5 with zaprinast (25 microM) reduced the amplitude and frequency of phasic contractions and increased the magnitude of inhibition produced by maximal concentrations of SNAP, suggesting that endogenous PDEs are constitutively active and regulate cGMP production. These results suggest that the NO-cGMP-PKG pathway may be involved in inhibitory control of the neonatal rat bladder.

Effects of long-term dietary soy treatment on female urethral morphology and function in ovariectomized nonhuman primates

PURPOSE

Agonistic effects of estrogen on the female urethra include an increase in contractile function, blood flow and mucosal hyperplasia. Whether such effects can be achieved by soy based phytoestrogen diets is unclear. We studied the effects of chronic phytoestrogen treatment on the structural and functional properties of the urethra in ovariectomized monkeys.

MATERIALS AND METHODS

Following ovariectomy 18 monkeys were fed a diet containing soy (9) or casein (9) based protein for 32 months. At necropsy the urethra and bladder were removed and the urethra was separated into 3 segments of equal length, including a proximal, a middle and a distal segment. Each urethral segment and 1 bladder segment was tested in vitro for functional responses to electrical field stimulation and pharmacological stimulation, and the proximal to distal segments were tested for urothelial thickness and mucosal area.

RESULTS

Electrical field stimulation produced frequency dependent contractile responses in the bladder, proximal and middle segments but not in the distal segment. Carbachol, phenylephrine and endothelin-1 produced concentration dependent contractions in all urethral segments. The maximum response decreased from the proximal to the distal segment (p </=0.05). The maximum response in the proximal and bladder segments to pharmacological stimulation and electrical field stimulation as well as mucosal area and urothelial thickness were significantly higher in the treatment than in the control group (p < or =0.05).

CONCLUSIONS

Chronic phytoestrogen treatment results in increased responsiveness of the proximal urethra to pharmacological and electrical stimulation, which is associated with an increase in urothelial thickness and mucosal area. This study indicates that dietary soy may have estrogen agonist effects on the urethra and bladder in estrogen deficient females.

Expression and distribution of cyclic GMP-dependent protein kinase-1 isoforms in human penile erectile tissue

INTRODUCTION

Besides the bioavailability of nitric oxide (NO), downstream guanine monophosphate (cGMP) effector proteins are also considered to play a significant role in penile vascular disease. In animal studies, a downregulation of the cGMP-dependent protein kinase-1 (cGKI) alpha isoform has been linked to erectile dysfunction and diabetes mellitus. So far, the expression of cGKI alpha and beta isoforms has not been evaluated in human penile erectile tissue.

AIM

To evaluate the expression of cGKI alpha and beta isoforms in relation to smooth muscle alpha-actin, cGMP, and endothelial NO synthase (eNOS) in human cavernous arteries (HCAs) and human corpus cavernosum (HCC).

METHODS

Cryostat sections of HCA and HCC were incubated with primary antibodies directed against alpha-actin, cGMP, eNOS, cGKI, cGKI alpha, and cGKI beta. Visualization of double-labeled immunofluorescent stainings was achieved by laser microscopy. Western blot analysis was performed in order to confirm the expression of cGKI isoforms.

MAIN OUTCOME MEASURES

Expression of cGKI alpha and beta isoforms in relation to smooth muscle alpha-actin, cGMP, and eNOS in human penile erectile tissue.

RESULTS

Immunoreactivities specific for cGKI, cGKI alpha, and cGKI beta were observed within the smooth musculature and the endothelium of cavernous arteries and sinusoids. Double stainings revealed the colocalization of alpha-actin, cGMP, eNOS, and cGKI isoforms. The expression of cGKI isoforms was confirmed by Western blot analysis.

CONCLUSIONS

Our results demonstrate, for the first time, the expression of both cGKI alpha and beta isoforms in the smooth musculature of HCA and HCC. Corresponding to recent findings from animal studies, the presence of cGKI alpha and beta provides further evidence for a significant role of these enzymes in the control of smooth muscle function in human penile erectile tissue.

Natriuretic peptide responsive, cyclic guanosine monophosphate producing structures in the guinea pig bladder

PURPOSE

We examined the localization of natriuretic peptide responsive, cyclic guanosine monophosphate producing cells in the guinea pig bladder.

MATERIALS AND METHODS

The bladder was removed from male guinea pigs sacrificed by cervical dislocation. The lateral wall of the bladder was cut into strips 2 mm thick. The tissue pieces were incubated in the presence of human atrial natriuretic peptide, rat brain natriuretic peptide and C-type natriuretic peptide or the nitric oxide donor DEANO (diethylamine NONOate or 1,1-diethyl-2-hydroxy-2-nitrosohydrazine) (Sigma). Cyclic guanosine monophosphate immunoreactivity was localized using an antibody against formaldehyde fixed cyclic guanosine monophosphate.

RESULTS

Atrial natriuretic peptide and brain natriuretic peptide stimulated cyclic guanosine monophosphate synthesis in suburothelial interstitial cells, whereas C-type natriuretic peptide was not effective. In contrast, DEANO stimulated cyclic guanosine monophosphate synthesis in urothelial umbrella cells, suburothelial interstitial cells, muscle interstitial cells and neurons. The effect of atrial natriuretic peptide and brain natriuretic peptide was not inhibited by ODQ (1H-[1, 2, 4]oxadiazolo[4-3a]quinoxalin-1-one), an inhibitor of nitric oxide responsive soluble guanylyl cyclase.

CONCLUSIONS

To our knowledge our findings show for the first time a localized effect of atrial natriuretic peptide and brain natriuretic peptide to the suburothelial cells of the guinea pig bladder. These cells express the soluble guanylyl cyclase and particulate guanylyl cyclase-A isoforms. The specific physiological role of these cells is not known but it was suggested that they may be involved in the generation or modulation of sensation. The results imply a role for natriuretic peptide-cyclic guanosine monophosphate signaling in the processing of sensory information in the bladder.

Immunohistochemical distribution of cyclic GMP-dependent protein kinase-1 in human prostate tissue

OBJECTIVES

Phosphodiesterase 5 (PDE5) inhibitors improve smooth muscle relaxation and therefore are considered for pharmacotherapy of benign prostatic hyperplasia (BPH) and lower urinary tract symptoms (LUTS). Cyclic guanosine monophosphate (cGMP)-dependent protein kinase-1 (cGKI) has been identified as one of the downstream targets for cGMP. The aim of the present study was to evaluate, by means of immunohistochemistry and Western blot analysis, the expression and localization of cGKI isoforms in relation to smooth muscle alpha-actin and cGMP in the human prostate.

METHODS

Cryostat sections of tissue segments excised from the transition zone of human prostates from 11 patients (aged 54-68 yr) were incubated with primary antibodies directed against smooth muscle alpha-actin, cGMP, cGKI, cGKIalpha, and cGKIbeta. Visualization of double-labelled immunofluorescent staining was achieved by laser microscopy. Western blot analysis was performed to confirm the expression of cGKI isoforms.

RESULTS

Immunoreactivities specific for cGKI, cGKIalpha, and cGKIbeta were observed in the smooth musculature of the transition zone. Double-staining revealed the colocalization of smooth muscle alpha-actin, cGMP, and cGKI isoforms in smooth muscle cells of the fibromuscular stroma. The expression of cGKI isoforms was confirmed by Western blot analysis.

CONCLUSIONS

Our results confirm the presence of cGKI isoforms alpha and beta in the transition zone of human prostate tissue. In addition, the colocalization of alpha-actin, cGMP, and cGKI isoforms provides further evidence for a significant role of the nitric oxide/cGMP pathway in the regulation of smooth muscle contractility in human prostate tissue and therefore could provide additional targets for pharmacotherapy of BPH and LUTS.

LUTS treatment: Future treatment options

Lower urinary tract symptoms (LUTS) are commonly divided into storage, voiding, and postmicturition symptoms, and may occur in both men and women. Male LUTS have historically been linked to benign prostatic hyperplasia (BPH), but are not necessarily prostate related. The focus of treatment for LUTS has thus shifted from the prostate to the bladder and other extraprostatic sites. LUTS include symptoms of the overactive bladder (OAB), which are often associated with detrusor overactivity. Treatment for LUTS suggestive of BPH has traditionally involved the use of alpha(1)-adrenoceptor (AR) antagonists; 5alpha-reductase inhibitors; and phytotherapy-however, several new therapeutic principles have shown promise. Selective beta(3)-adrenoceptor agonists and antimuscarinics are potentially useful agents for treating LUTS, particularly for storage symptoms secondary to outflow obstruction. Other agents of potential or actual importance are antagonists of P2X(3) receptors, botulinum toxin type A, endothelin (ET)-converting enzyme inhibitors, and drugs acting at vanilloid, angiotensin, and vitamin D(3) receptor sites. Drugs interfering with the nitric oxide/cGMP-cAMP pathway, Rho-kinase and COX inhibitors, as well as drugs targeting receptors and mechanisms within the CNS, are also of interest and deserving of further study for the treatment of LUTS.

Activation of the cGMP/PKG pathway inhibits electrical activity in rabbit urethral interstitial cells of Cajal by reducing the spatial spread of Ca2+ waves

In the present study we used a combination of patch clamping and fast confocal Ca2+ imaging to examine the effects of activators of the nitric oxide (NO)/cGMP pathway on pacemaker activity in freshly dispersed ICC from the rabbit urethra, using the amphotericin B perforated patch configuration of the patch-clamp technique. The nitric oxide donor, DEA-NO, the soluble guanylyl cyclase activator YC-1 and the membrane-permeant analogue of cGMP, 8-Br-cGMP inhibited spontaneous transient depolarizations (STDs) and spontaneous transient inward currents (STICs) recorded under current-clamp and voltage-clamp conditions, respectively. Caffeine-evoked Cl- currents were unaltered in the presence of SP-8-Br-PET-cGMPs, suggesting that activation of the cGMP/PKG pathway does not block Cl- channels directly or interfere with Ca2+ release via ryanodine receptors (RyR). However, noradrenaline-evoked Cl- currents were attenuated by SP-8-Br-PET-cGMPs, suggesting that activation of cGMP-dependent protein kinase (PKG) may modulate release of Ca2+ via IP3 receptors (IP3R). When urethral interstitial cells (ICC) were loaded with Fluo4-AM (2 microm), and viewed with a confocal microscope, they fired regular propagating Ca2+ waves, which originated in one or more regions of the cell. Application of DEA-NO or other activators of the cGMP/PKG pathway did not significantly affect the oscillation frequency of these cells, but did significantly reduce their spatial spread. These effects were mimicked by the IP3R blocker, 2-APB (100 microm). These data suggest that NO donors and activators of the cGMP pathway inhibit electrical activity of urethral ICC by reducing the spatial spread of Ca2+ waves, rather than decreasing wave frequency.

Phosphodiesterase 5 in the female pig and human urethra: morphological and functional aspects

OBJECTIVE

To characterize the distribution of phosphodiesterase 5 (PDE-5), cGMP and cGMP-dependent protein kinase I (PKG1), and to evaluate the effect of pharmacological inhibition of PDE-5 in isolated preparations of pig and human urethra, as the nitric oxide (NO)/cGMP pathway generates the main inhibitory signals to reduce resistance in the bladder outlet and urethra during emptying of the bladder.

MATERIALS AND METHODS

After obtaining ethics committee approval, urethral specimens were obtained from three female patients during cystectomy, and from young female pigs. The specimens were prepared for immunohistochemical investigations and for functional studies in organ baths. Effects of sildenafil, vardenafil and tadalafil (1 nm to 30 microm) were studied in l-noradrenaline (1 microm)-activated or spontaneously contracted preparations, and on relaxations induced by electrical-field stimulation (EFS). Levels of cGMP were determined by radioimmunoassay.

RESULTS

After stimulation with the NO donor, DETA NONO-ate (1 mm), there was greater cGMP-immunoreactivity (IR) in urethral and vascular smooth muscles. There was a wide distribution of cGMP- and vimentin-positive interstitial cells between pig urethral smooth muscle bundles. There was also cGMP-IR within NO-synthase-IR endothelium. There was PDE-5 IR within the urethral and vascular smooth muscle cells, but also in vascular endothelial cells that expressed cGMP-IR. In pig and human sections, there was strong PKG1-IR in alpha-actin-IR urethral smooth muscle cells that also contained IR for cGMP. Sildenafil, vardenafil and tadalafil caused mean (sem) concentration-dependent relaxations of the pig urethra which, at 30 microm, were 80 (3)% (11 samples), 81 (5)% (12 samples) and 64 (4)% (10 samples) of the spontaneous tone. The relaxation of L-noradrenaline-contracted female human urethra was 100% in response to 10 microm sildenafil, and 85 (15)% and 47 (13)% for 30 microm of vardenafil and tadalafil, respectively (three samples). Vardenafil or sildenafil (30 microm) doubled cGMP levels in pig specimens. There were no effects on cGMP levels with tadalafil. EFS (1-32 Hz) caused l-NG-nitroarginine-sensitive relaxations of pig urethral muscle that were increased in amplitude and duration by PDE-5 inhibition. At 0.1 microm, sildenafil, vardenafil or tadalafil significantly prolonged the mean (sem) duration of the relaxation at 4 Hz by 55 (19)%, 45 (14)% and 51 (12)%, respectively.

CONCLUSIONS

PDE-5-, cGMP- and PKG1-IR is widely distributed in human and pig urethral tissues. Nerve-induced relaxations of urethral preparations were enhanced at low concentrations of sildenafil, vardenafil and tadalafil, whereas there were direct smooth muscle-relaxant actions of the PDE-5 inhibitors at high concentrations. Inhibition of PDE-5 might be an interesting option to facilitate cGMP-mediated relaxation of the outflow region.

Interstitial cells of Cajal in the urethra

The smooth muscle layer of the urethra generates spontaneous myogenic tone that is thought to make a major contribution to urinary continence. The mechanisms underlying generation of tone remain unclear, however recent studies from our laboratory highlighted a role for a specialised population of pacemaker cells which we originally referred to as interstitial cells (IC) and now term ICC. Urethra ICC possess an electrical pacemaker mechanism characterised by rhythmic activation of Ca(2+)-activated Cl(-) channels leading to spontaneous transient inward currents (STICs) under voltage clamp and spontaneous transient depolarisations (STDs) under current clamp conditions. Both STICS and STDs are now known to be associated with spontaneous Ca(2+) oscillations that result from a complex interplay between release of Ca(2+) from intracellular stores and Ca(2+) influx across the plasma membrane. In this review we will consider some of the precise mechanisms involved in the generation of pacemaker activity and discuss how these are modulated by excitatory and inhibitory neurotransmitters.

Function of cGMP-Dependent Protein Kinases as Revealed by Gene Deletion

Over the past few years, a wealth of biochemical and functional data have been gathered on mammalian cGMP-dependent protein kinases (cGKs). In mammals, three different kinases are encoded by two genes. Mutant and chimeric cGK proteins generated by molecular biology techniques yielded important biochemical knowledge, such as the function of the NH2-terminal domains of cGKI and cGKII, the identity of the cGMP-binding sites of cGKI, and the substrate specificity of the enzymes. Genetic approaches have proven especially useful for the analysis of the biological functions of cGKs. Recently, some of the in vivo targets and mechanisms leading to changes in neuronal adaptation, smooth muscle relaxation and growth, intestinal water secretion, bone growth, renin secretion, and other important functions have been identified. These data show that cGKs are signaling molecules involved in many biological functions.

Nitric oxide/cGMP-mediated effects in the outflow region of the lower urinary tract--is there a basis for pharmacological targeting of cGMP?

Treatment with alpha-adrenoceptor antagonists that reduce the tone of prostatic stromal and urethral smooth muscle has beneficial effects in patients with benign prostatic hyperplasia (BPH) and lower urinary tracts symptoms (LUTS) and has brought attention to regulatory mechanisms of smooth muscle contractility of the outflow region. The prostate, urethra and bladder neck are densely supplied by nitric oxide (NO)-synthase-containing nerves that cause relaxation upon activation. In various experimental models, altered function or activity of the NO/cGMP pathway of the bladder neck and urethra may be related to inappropriate or un-coordinated functions of the bladder outlet and detrusor, but causal connections between alterations in this signaling system, a dysfunctional bladder outlet, and the development of LUTS are not established for humans. The present review focuses on regulatory functions of smooth muscle contractility by the NO/cGMP-pathway in the bladder neck, urethra, and prostate. Disease-related alterations in the NO/cGMP-pathway, and putative options for pharmacological modification of this signaling pathway in the out-flow region are briefly discussed.