Non-adrenergic, non-cholinergic relaxation and levels of cyclic nucleotides in rabbit lower urinary tract

Expression of Phosphodiesterase (PDE) Isoenzymes in the Human Male and Female Urethra

Purpose

Although it has been supposed that the NO/cyclic GMP system produces inhibitory signals to reduce the resistance of the bladder outlet and urethra during the micturition phase, little is known on the mechanisms controlling the function of urethral smooth muscle. The aim of the present study was to examine in the male and female urethra the expression of phosphodiesterase (PDE) isoenzymes, known as key proteins of the cyclic GMP/AMP signaling.

Methods

Urethral tissue was obtained from 4 female cadavers and 7 male patients (who had undergone gender reassignment surgery). The expression of mRNA encoding for PDE1A, 1B, 1C, 2A, 4B, 4D, 5A, 10A and 11A was investigated by means of real-time polymerase chain reaction. Western blot (WB) analysis was conducted to detect PDE isoenzymes.

Results

RT-PCR revealed relevant amounts of mRNA encoding for PDE1A, 2A, 4B, 5A, 10A and 11A in male and female urethral tissue. The expression of PDE1A, 2A, 4B and 10A was 2-fold higher in the female than in the male urethra, whereas the expression of PDE11A mRNA was 7-fold higher in the male tissue. In the WB experiments, immunosignals specific for PDE1A, PDE4A and 4B and PDE11A were of higher degree in the female than the male tissue specimens, while an almost equivocal expression of PDE2A, PDE5A and PDE10A was registered.

Conclusion

On the level of mRNA and function proteins, different patterns of expression of PDE isoenzymes were registered in human male and female urethra. Future studies may clarify whether inhibition of PDE isoenzymes is likely to facilitate the relaxation of the outflow region in both sexes.

Urethral dysfunction and alterations of nitric oxide mechanisms in streptozotocin-induced diabetic rats with or without low-dose insulin treatment

AIMS

To establish an animal model of diabetes mellitus (DM) with moderately elevated blood glucose levels, and to examine the nitric oxide (NO) mechanism controlling urethral function in streptozotocin (STZ)-induced DM rats.

MAIN METHODS

Female Sprague-Dawley rats were used. DM was induced by intraperitoneal injection of STZ (65 mg/kg) and some of them received subcutaneous implantation of a low-dose insulin pellet. Voiding behavior was evaluated in metabolic cages. Isovolumetric cystometry and urethral perfusion pressure (UPP) were then evaluated under urethane anesthesia, during which L-arginine (100 mg/kg) and N-nitro-L-arginine methyl ester hydrochloride (L-NAME) (50 mg/kg) were administered intravenously. In vitro urethral activity was also tested by organ bath muscle strip studies.

KEY FINDINGS

UPP changes and high-frequency oscillation (HFO) were significantly (P < 0.05) smaller in 8-weeks DM rats vs. normal control (NC) rats or insulin-treated DM rats, which showed reductions in urine overproduction and voided volume per micturition vs. untreated DM rats. UPP nadir was decreased by L-arginine in NC and insulin-treated DM groups, and decreased by L-NAME in all groups. Five of 6 untreated DM rats showed a detrusor-sphincter dyssynergia pattern after L-NAME. In in vitro studies, the relative ratio of L-NAME-induced reductions of urethral relaxation against pre-drug urethral relaxation was significantly smaller in DM vs. NC rats (P < 0.05).

SIGNIFICANCE

Low-dose insulin-treated DM rats would be a useful model for studying natural progression of DM-induced lower urinary tract dysfunction. The impaired NO-mediated urethral relaxation mechanisms play an important role in DM-induced urethral dysfunction, which could contribute to DM-induced inefficient voiding.

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.

Sex differences in lower urinary tract biology and physiology

Females and males differ significantly in gross anatomy and physiology of the lower urinary tract, and these differences are commonly discussed in the medical and scientific literature. However, less attention is dedicated to investigating the varied development, function, and biology between females and males on a cellular level. Recognizing that cell biology is not uniform, especially in the lower urinary tract of females and males, is crucial for providing context and relevance for diverse fields of biomedical investigation. This review serves to characterize the current understanding of biological sex differences between female and male lower urinary tracts, while identifying areas for future research. First, the differences in overall cell populations are discussed in the detrusor smooth muscle, urothelium, and trigone. Second, the urethra is discussed, including anatomic discussions of the female and male urethra followed by discussions of cellular differences in the urothelial and muscular layers. The pelvic floor is then reviewed, followed by an examination of the sex differences in hormonal regulation, the urinary tract microbiome, and the reticuloendothelial system. Understanding the complex and dynamic development, anatomy, and physiology of the lower urinary tract should be contextualized by the sex differences described in this review.

Soluble guanylyl cyclase (sGC) degradation and impairment of nitric oxide-mediated responses in urethra from obese mice: reversal by the sGC activator BAY 60-2770

Obesity has emerged as a major contributing risk factor for overactive bladder (OAB), but no study examined urethral smooth muscle (USM) dysfunction as a predisposing factor to obesity-induced OAB. This study investigated the USM relaxant machinery in obese mice and whether soluble guanylyl cyclase (sGC) activation with BAY 60-2770 [acid 4-({(4-carboxybutyl) [2-(5-fluoro-2-{[4-(trifluoromethyl) biphenyl-4-yl] methoxy} phenyl) ethyl] amino} methyl) benzoic] rescues the urethral reactivity through improvement of sGC-cGMP (cyclic guanosine monophosphate) signaling. Male C57BL/6 mice were fed for 12 weeks with a high-fat diet to induce obesity. Separate groups of animals were treated with BAY 60-2770 (1 mg/kg per day for 2 weeks). Functional assays and measurements of cGMP, reactive-oxygen species (ROS), and sGC protein expression in USM were determined. USM relaxations induced by NO (acidified sodium nitrite), NO donors (S-nitrosoglutathione and glyceryl trinitrate), and BAY 41-2272 [5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-pyrimidin-4-ylamine] (sGC stimulator) were markedly reduced in obese compared with lean mice. In contrast, USM relaxations induced by BAY 60-2770 (sGC activator) were 43% greater in obese mice (P < 0.05), which was accompanied by increases in cGMP levels. Oxidation of sGC with ODQ [1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one] (10 μM) potentiated BAY 60-2770-induced USM responses in the lean group. Long-term oral BAY 60-2770 administration fully prevented the impairment of USM relaxations in obese mice. Reactive-oxygen species (ROS) production was enhanced, but protein expression of β1 second guanylate cyclase subunit was reduced in USM from obese mice, both of which were restored by BAY 60-2770 treatment. In conclusion, impaired USM relaxation in obese mice is associated with ROS generation and down-regulation of sGC-cGMP signaling. Prevention of sGC degradation by BAY 60-2770 ameliorates the impairment of urethral relaxations in obese mice.

Pelvic ischemia is measurable and symptomatic in patients with coronary artery disease: a novel application of dynamic contrast-enhanced magnetic resonance imaging

INTRODUCTION

Pelvic ischemia can manifest as vascular-mediated erectile dysfunction (ED) and lower urinary tract symptoms (LUTS), and is associated with cardiac ischemia.

AIMS

We aimed to develop a dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) technique to measure pelvic perfusion in benign tissue.

METHODS

Nine men with coronary artery disease (CAD) were compared with nine without. Images were acquired at 3T with T1-weighted DCE-MRI for perfusion. Two-compartment pharmacokinetic modeling was employed to fit signal enhancement from prostate, corpus cavernosal, and spongiosal tissues.

MAIN OUTCOME MEASURES

Perfusion parameters and validated pelvic symptom scores were compared.

RESULTS

The mean International Index of Erectile Function (IIEF) total score was worse in CAD (41.3 +/- 19.7) vs. controls (59.4 +/- 14.9, P = 0.04). The IIEF erectile function domain score trended to worse in CAD (13.7 +/- 9.7) vs. controls (22.0 +/- 9.9, P = 0.09). The mean total International Prostate Symptom Score (IPSS) trended to worse in CAD patients (13.2) than controls (7.0) (P = 0.10). Magnetic resonance perfusion analysis demonstrated lower mean maximal percent enhancement to P < 0.0001 in the CAD group vs. controls for all the following comparisons: prostate in CAD (22.4 +/- 0.4) vs. controls (26.3 +/- 0.1); cavernosal tissue in CAD (9.3 +/- 0.2) vs. controls (16.6 +/- 0.8); and spongiosal tissue in CAD (20.6 +/- 1.2) vs. controls (24.0 +/- 0.6). Comparison of mean wash-in rates in the unit of 10(-3)/second was also highly significant (P < 0.0001 for all tissues): prostate in CAD (574.0 +/- 18.0) was lower than controls (1,035.0 +/- 29.0); slower wash-in rates were seen in CAD cavernosal (58.0 +/- 4.0 vs. 139.0 +/- 9.0 in controls) and spongiosal tissue (134.0 +/- 6.0 vs. 278.0 +/- 12.0 in controls).

CONCLUSION

These initial data demonstrate that pelvic perfusion can be measured in noncancerous tissues, and that perfusion correlates with validated measures of ED and LUTS.

Interstitial cells of Cajal in the urethra are cGMP-mediated targets of nitrergic neurotransmission

While interstitial cells of Cajal (ICC) in the urethra respond to nitric oxide (NO) donors by increasing cGMP, it remains unclear whether urethral ICC are functionally innervated by nitrergic nerves. We have addressed this issue in the rat and sheep urethra, where cGMP production and relaxation were compared in preparations subjected to electrical field stimulation (EFS; 2 Hz, 4 min) of nitrergic nerves or to exogenous S-nitroso-L-cysteine (SNC; 0.1 mM, 4 min). Upon EFS, cGMP immunoreactivity (cGMP-ir) was observed in both smooth muscle cells (SMC) and in spindle-shaped cells that contained c-kit and vimentin, features of ICC. Similarly, cGMP-ir was preferentially, but inconsistently, found in ICC of the outer muscle layer on exposure to SNC. We found separate functional groups of ICC within the urethra. Thus only ICC present in the muscle layers (ICC-M) but not those in the serosa (ICC-SR) and lamina propia (ICC-LP) seem to be specifically influenced by activation of neuronal NO synthase (nNOS). Thus the increase in cGMP-ir in the ICC-M induced by EFS was prevented by Nomega-nitro-L-arginine and ODQ. Urethral ICC did not express nNOS, although they were closely associated with nitrergic nerves. cGMP-ir was also present in the urothelium (in the rat but not in the sheep) and the vascular endothelium but not in neural structures, such as the nerve trunks and nerve terminals. Together, these results suggest a model of parallel innervation in which both SMC and ICC-M are effectors of nerve-released NO in the urethra.

The immediate effect of nitric oxide on the rabbit bladder after ovariectomy

Ovariectomy resulted in decreased blood flow and hypoxia to the bladder mucosa and smooth muscle. Nitric oxide (NO) played an important role in regulating bladder function during bladder ischemia and reperfusion. This study was designed to evaluate the role of NO on bladder function in the first few days after ovariectomy. Female rabbits were separated into three groups, one which received no medication, premedicated with N(omega)-nitro-L-arginine methyl ester (L-NAME) and the third treated with L-arginine. Non-ovariectomized controls and at 1 and 3 days post-ovariectomy, animals from each group were euthanized. Cystometry and in vitro isometric contractile responses were recorded and the oxidative stress markers, nitrotyrosine and protein carbonylation were determined. L-NAME treatment did not significantly alter bladder function after ovariectomy. L-Arginine fed, ovariectomized rabbits had lower intravesical pressure and better contractile responses to all forms of stimulation than the ovariectomized rabbits with or without L-NAME. Furthermore, the ovariectomized ones with or without L-NAME had higher oxidative stress markers than L-arginine fed rabbits. This study clearly demonstrates that feeding rabbits with L-arginine can protect the bladder from oxidative free radical damage following short-term ovariectomy.

Increased cyclic guanosine monophosphate synthesis and calcium entry blockade account for the relaxant activity of the nitric oxide-independent soluble guanylyl cyclase stimulator BAY 41-2272 in the rabbit penile urethra

OBJECTIVES

To study the direct relaxant activity of 5-cyclopropyl-2-[1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]pyrimidin-4-ylamine (BAY 41-2272) in the rabbit penile urethra and to investigate its modulatory effect on nitric oxide (NO)-mediated responses.

METHODS

Urothelium-intact (U+) and denuded (U-) rings were mounted in 10-mL organ baths for isometric force recording. Intracellular cyclic guanosine monophosphate (cGMP) levels were quantified with specific kits.

RESULTS

BAY 41-2272 (0.0001 to 10 micromol/L) caused relaxation of urethral rings contracted with phenylephrine (10 micromol/L), with higher potency (P <0.01) in U+ (pEC(50) 7.77 +/- 0.09) compared with U- (pEC(50) 6.84 +/- 0.19) preparations. The NO synthesis inhibitor N(omega)-nitro-L-arginine methyl ester (100 micromol/L) or the soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3,-a]quinoxalin-1-one (ODQ) (10 micromol/L) had no effect on BAY 41-2272 responses in U+ or U- rings. The phosphodiesterase-5 inhibitor vardenafil (0.1 micromol/L) potentiated the relaxant effects of BAY 41-2272 in both U+ (10-fold) and U- (sevenfold) tissues. Ca(2+)-induced contractions in K(+) depolarized rings were significantly attenuated by BAY 41-2272 (1 micromol/L) in an ODQ-insensitive manner. BAY 41-2272 (0.03-0.3 micromol/L) increased the amplitude and duration of electrical field stimulation-induced relaxations (1 to 32 Hz), as well as those evoked by the NO donor glyceryl trinitrate (0.0001 to 10 micromol/L). BAY 41-2272 induced ODQ-resistant increases in cGMP levels above baseline (approximately twofold) in both U+ and U- rings.

CONCLUSIONS

BAY 41-2272 relaxes penile urethra in a synergic fashion with NO. Targeting soluble guanylate cyclase with BAY 41-2272 may represent a new therapy in the management of voiding disturbances associated with impaired NO-cGMP signaling.

Testosterone decreased urinary-frequency in nNOS-deficient mice

To observe the effect of testosterone on the frequency of urination in mice lacking neuronal nitric oxide synthase (nNOS(-/-)), we compared the urination patterns between unanaesthetized male wild-type (n = 27) and nNOS(-/-) mice (n = 50) with or without testosterone treatment. Compared with wild-type mice, nNOS(-/-) mice showed a greater frequency of urination during a 24-h observation period (3.0 vs. 5.4 times/day, p < 0.0001) without any significant difference in the total voided volume or the functional voiding capacity. While testosterone treatment did not affect the urination patterns in wild-type, it decreased the daytime frequency of urination (5.4 vs. 3.7 times, p = 0.0198) and the nighttime urination (4.4 vs. 2.9 times, p = 0.039) in nNOS(-/-) mice. The nNOS(-/-) mice can be a useful animal model for urinary frequency. Testosterone improved the functional abnormalities in the voiding of nNOS(-/-) mice.

Oscillatory membrane currents paradoxically induced via NO-activated pathways in detrusor cells

Oscillatory inward membrane currents (I(oscil-in)) reflecting intracellular Ca(2+) ([Ca(2+)](i)) activity in detrusor cells, are thought to play an important role in producing tonic bladder contractions during micturition. The present patch clamp study revealed a new activation mechanism: sodium nitroprusside (SNP), a nitric oxide (NO) donor induced I(oscil-in) in a subpopulation of detrusor cells. The inhibitory effect of niflumic acid on SNP-induced I(oscil-in) suggests that Ca(2+)-activated Cl(-) channels are responsible for this current. In addition, SNP-induced I(oscil-in) required the cooperation of Ca(2+) influx through SK&F96365-sensitive channels and intracellular Ca(2+) release channels sensitive to ryanodine but insensitive to xestospongin C (XeC). This is also true for muscarinic agonist (carbachol: CCh)-induced I(oscil-in). However, 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a guanylyl cyclase inhibitor, suppressed SNP-induced I(oscil-in) but not CCh-induced I(oscil-in). The results suggest that a subpopulation of detrusor cells employ the NO/cGMP cascade to potentiate bladder contraction. Mechanisms underlying NO-induced I(oscil-in) are likely to contribute not only to the physiology but also to the pathophysiology of the lower urinary tract.

Phosphodiesterases (PDEs) and PDE inhibitors for treatment of LUTS

Lower urinary tract (LUT) smooth muscle can be relaxed by drugs that increase intracellular concentrations of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Both of these substances are degraded by phosphodiesterases (PDEs), which play a central role in the regulation of smooth muscle tone. The distribution and functional significance of PDE enzymes vary in different tissues of the LUT. Targeting specific PDE isoenzymes should thus allow organ selectivity. PDE 4 and 5 appear to predominate in the prostate, PDE 1 and 4 are thought to influence detrusor smooth muscle function, and PDE 5 may be functionally important in the urethra and vasculature. Studies on the use of PDE inhibitors to treat various LUT symptoms (LUTS), have yielded favorable results. Thus, positive effects of the PDE 5 inhibitors sildenafil and tadalafil on symptoms and quality of life in men with LUTS, erectile dysfunction, and BPH have also been demonstrated. These effects may be due to effects on cGMP signaling and/or modification of afferent input from bladder, urethral, and prostate tissue. This review gives an update on the distribution of PDEs in structures relevant for LUT function, and discusses how inhibition of these enzymes can contribute to beneficial effects on LUTS. Information for the review was obtained from searches of the PubMed database, and from the authors' files.

Effects of phosphodiesterase type 5 inhibitor on the contractility of prostate tissues and urethral pressure responses in a rat model of benign prostate hyperplasia

AIM

This study was performed to investigate the effect of DA-8159, a selective phosphodiesterase 5 (PDE5) inhibitor, on benign prostatic hyperplasia (BPH) both in vitro and in vivo.

METHODS

We assessed the influence of DA-8159 on the contractility of rat prostate tissues in an organ-bath experiment. In addition, in order to investigate whether chronic administration of DA-8159 prevents the increase of electrostimulation-induced intraurethral pressure (IUP) responses associated with BPH, BPH was induced by steroid hormones (testosterone plus 17beta-estradiol) and DA-8159 (5, 20 mg/kg) was concomitantly administered once a day for 8 weeks. After that the electrostimulation-induced IUP responses were measured. Finally, we investigated the acute treatment effect of DA-8159 on IUP responses in an established BPH model after a single intravenous injection of DA-8159 (0.3, 1 mg/kg).

RESULTS

DA-8159 concentration-dependently reduced the contraction of the isolated prostate strips with an IC50 value of 70 microM. In chronic treatment study, while the BPH control rats showed a significantly increased IUP both at the baseline and by electrostimulation, the chronic DA-8159 treatment significantly attenuated the increase in IUP responses in a dose- and frequency-dependent manner. In the acute treatment study, a single intravenous injection of DA-8159 also prevented the increase in urethral pressure in a dose-dependent manner.

CONCLUSIONS

These results suggest that DA-8159 may be beneficial on lowering the urethral pressure associated with BPH via dilatation of the prostate, but a further evaluation of the efficacy on humans needs to be performed.

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.

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.

Pharmacology of the lower urinary tract: basis for current and future treatments of urinary incontinence

The lower urinary tract constitutes a functional unit controlled by a complex interplay between the central and peripheral nervous systems and local regulatory factors. In the adult, micturition is controlled by a spinobulbospinal reflex, which is under suprapontine control. Several central nervous system transmitters can modulate voiding, as well as, potentially, drugs affecting voiding; for example, noradrenaline, GABA, or dopamine receptors and mechanisms may be therapeutically useful. Peripherally, lower urinary tract function is dependent on the concerted action of the smooth and striated muscles of the urinary bladder, urethra, and periurethral region. Various neurotransmitters, including acetylcholine, noradrenaline, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in this neural regulation. Muscarinic receptors mediate normal bladder contraction as well as at least the main part of contraction in the overactive bladder. Disorders of micturition can roughly be classified as disturbances of storage or disturbances of emptying. Failure to store urine may lead to various forms of incontinence, the main forms of which are urge and stress incontinence. The etiology and pathophysiology of these disorders remain incompletely known, which is reflected in the fact that current drug treatment includes a relatively small number of more or less well-documented alternatives. Antimuscarinics are the main-stay of pharmacological treatment of the overactive bladder syndrome, which is characterized by urgency, frequency, and urge incontinence. Accepted drug treatments of stress incontinence are currently scarce, but new alternatives are emerging. New targets for control of micturition are being defined, but further research is needed to advance the pharmacological treatment of micturition disorders.

Oral nitric oxide donors: a new pharmacological approach to detrusor-sphincter dyssynergia in spinal cord injured patients?

PURPOSE

Detrusor-sphincter dyssynergia is a common cause of bladder outlet obstruction in spinal cord injured patients and leads to poor bladder emptying and high bladder pressures, which if left untreated might cause renal failure. In this study, we tested the recently published hypothesis that oral administration of a nitric oxide donor could be a new pharmacological approach to treat detrusor-sphincter dyssynergia in humans with spinal cord injury.

METHODS

12 male spinal cord injured patients presenting with neurogenic detrusor overactivity and detrusor-sphincter dyssynergia were studied. 6 performed clean intermittent catheterisation and 6 used suprapubic tapping for bladder emptying. During cystometry the bladder was filled until the first overactive bladder contraction accompanied by detrusor-sphincter dyssynergia occurred while bladder and external urethral sphincter pressures were continuously recorded. Then the bladder was emptied and the patients received 10 mg of isosorbide dinitrate sublingually. Resting pressures were recorded and cystometry was repeated starting 15 min after drug administration. Maximal and mean values for bladder and external urethral sphincter pressures were calculated in both fillings and statistically compared by analysis of variance for repeated measurements (level of significance p < 0.05).

RESULTS

Nitric oxide significantly reduced external urethral sphincter pressures at rest (p < 0.05) and during dyssynergic contraction (p < 0.05) while bladder pressures at rest and during contraction as well as the reflex volume remained unchanged. In the patients who used suprapubic tapping for bladder emptying the mean post triggering residual volume was significantly reduced (p < 0.05).

CONCLUSIONS

Oral administration of nitric oxide donors significantly reduced bladder outlet obstruction due to detrusor-sphincter dyssynergia suggesting a role for nitric oxide in inhibitory neurotransmission to the urethral sphincter. This new approach could offer a potential pharmacological option to treat detrusor-sphincter dyssynergia in spinal cord injured patients.

The effect of nitric oxide on the resting tone and the contractile behaviour of the external urethral sphincter: a functional urodynamic study in healthy humans

AIMS

This functional urodynamic study assessed the effect of the nitric oxide donor isosorbide dinitrate on the external urethral sphincter and hypothesised first that nitric oxide could lower the resting sphincter pressure, second that nitric oxide could influence the sphincter contractility during magnetic stimulation, and third that nitric oxide could induce a faster external urethral sphincter fatigue during continuous magnetic stimulation.

METHODS

Eight healthy males gave their written informed consent and were included. A 2-channel microtip pressure transducer catheter was inserted into the urethra measuring the bladder and the external urethral sphincter pressure. Magnetic stimulation of the sacral roots was performed to evoke reproducible contractions of the external urethral sphincter. The baseline protocol included six single pulse stimulations and three stimulations 10sec in duration each for two frequencies 5Hz and 50Hz with intensities at the motor threshold of the pelvic floor. Then the subjects received 10 mg of isosorbide nitrate sublingually and the protocol was repeated 5min, 20min, 40min and 60min after drug administration.

RESULTS

The sublingual administration of isosorbide dinitrate could significantly reduce the resting pressure of the external urethral sphincter for at least one hour. The maximal contractile strength measured as the maximal urethral pressure during single pulse and continuous magnetic stimulation of the sacral roots also decreased significantly. Nitric oxide did not induce a significantly faster fatigue of the external urethral sphincter during continuous magnetic stimulation of the sacral roots.

CONCLUSIONS

This study shows a functionally relevant effect of nitric oxide on the resting tone and the contractile behaviour of the human external urethral sphincter in vivo while the fatigue properties did not changed significantly. Nitric oxide donors could offer a new pharmacological approach to treat urinary retention due to overactive or non-relaxing external urethral sphincter.

The effect of intravesical sodium nitroprusside on idiopathic detrusor overactivity

Although nitric oxide (NO) plays an important role in the urethra and outlet region of the bladder, the role of this inhibitory neurotransmitter in the human detrusor remains unclear. We conducted a prospective, randomised, open study on 31 patients with urodynamically proven idiopathic detrusor overactivity in order to examine the effects of intravesical administration of the NO donor sodium nitroprusside (SNP) on detrusor overactivity. Thirty-one consecutive patients (14 male, 17 female; mean age 53.0+/-2.7 years) with idiopathic detrusor overactivity diagnosed by pressure-flow analysis were included in this study. The patients were randomised into two groups. Cystometries were performed with normal saline in the control group ( n=10) and with 7.2 mM SNP solution (2.16 mg/ml) in the study group ( n=21). We urodynamically investigated sensation, maximal cystometric capacity, compliance, instability index, amplitude and frequency of involuntary contractions. No statistically significant differences was found between the first (pressure-flow) and second (saline or SNP cystometry) urodynamic values in the control and study groups (P>0.05). We have demonstrated that SNP does not have any effect on uninhibited bladder contractions. These results suggest that the intravesical administration of SNP is not an effective treatment for detrusor overactivity.

[Regulation by autonomic nerves of bladder neck sphincter function--mainly on inhibitory NANC nerves]

This article describes current information concerning analyses of contraction and relaxation associated with electrical stimulation of efferent nerves in isolated mammalian sphincter muscles. Contractile responses of sphincters are mediated by alpha 1-adrenoceptors and muscarinic receptors stimulated by transmitters from adrenergic and cholinergic nerves, respectively, whereas those of the bladder body are almost exclusively mediated by transmitters from parasympathetic nerves. Relaxant responses to nerve stimulation are ascribed mainly to mechanisms that are sensitive and resistant to nitric oxide (NO) synthase inhibitors. Neurogenic calcitonin gene-related peptide and beta-adrenoceptor activation by neurogenic norepinephrine may also be involved in some mammals. Stimulus frequency is an important determinant to distinguish NO synthase-sensitive and -resistant components; responses at low frequencies are abolished by the enzyme inhibitors, whereas those at high frequencies are inhibited only partially. High and low frequency stimulation increases the cyclic GMP content in muscles, suggesting the involvement of neurogenic NO, although relaxation at high frequencies is only partially due to such a mechanism. From pharmacological studies so far analyzed, including ours performed with porcine urinary tract sphincters, it is concluded that NO synthase resistant-relaxation is not mediated by peptides nor compounds that open K+ channels in muscle cell membrane and stimulate beta-adrenoceptors. Contribution of NO and non-NO relaxing factor (s) in relaxant responses varies with animal species. Identification of this factor, determination of intracellular signaling processes and interaction with the NO/cyclic GMP system may give us a clue in developing new therapeutics to treat dysfunctions of the lower urinary tract sphincters.

Sildenafil influences lower urinary tract symptoms

OBJECTIVE

To assess the possible relationship between erectile dysfunction (ED) and lower urinary tract symptoms (LUTS) in men, and whether treatment of their ED with sildenafil influences their LUTS.

PATIENTS AND METHODS

In all, 112 men with ED attending the andrology outpatient clinic were offered oral sildenafil and reviewed 1 and 3 months after treatment. They completed the International Index of Erectile Function and the International Prostate Symptom Score (IPSS) questionnaires at baseline and each review. Scores were designated to indicate the visit number and differences between the visits calculated.

RESULTS

A third of the men had an initial IPSS of > 7; there was no relationship between baseline urinary and sexual function scores. After treatment with sildenafil, the urinary scores at 3 months correlated strongly with the sexual function scores. There was a significant inverse relationship between the baseline IPSS and sexual function scores after treatment. The overall trend in the IPSS was towards improvement after treatment with sildenafil.

CONCLUSIONS

In men with ED there is no relationship between sexual function scores and urinary symptom scores before treating ED. Treatment with sildenafil appears to improve urinary symptom scores. A lower IPSS at baseline appears to predict a better response to ED therapy with sildenafil.

An investigation of the effects of zaprinast, a PDE inhibitor, on the nitrergic control of the urethra in anaesthetized female rats

1. The effects of L-NAME and zaprinast were investigated (i.v.) on reflex-evoked changes in bladder and urethral pressures in urethane-anaesthetized female rats. 2. L-NAME attenuated reflex-evoked urethral relaxations (65+/-10%), while zaprinast potentiated these responses (68+/-24%). L-NAME and zaprinast also increased baseline urethral pressure and urethral striated muscle (EUS-EMG) activity. These drugs had little effect on the bladder. 3. Following pre-treatment with alpha-bungarotoxin (i.v.) to block urethral striated muscle, L-NAME and zaprinast failed to increase baseline urethral pressure. Further zaprinast failed to alter the size of reflex-evoked urethral relaxations. 4. Intra-urethral zaprinast caused a significant increase while sodium nitroprusside (SNP) and isoprenaline caused decreases in urethral pressure (+14+/-3%, -25+/-5%, -29+/-7%, respectively). These changes were associated with increases in EUS-EMG activity. After chlorisondamine (i.v.), zaprinast caused a significant fall in urethral pressure, while the decrease in urethral pressure caused by SNP and isoprenaline was potentiated. No changes in EUS-EMG activity occurred. 5. These results indicate that a nitrergic pathway mediates reflex-evoked urethral smooth muscle relaxations. The data also indicates that there is a background release of NO, which reduces sphincter skeletal muscle activity. Further, the ability of zaprinast to potentiate nitrergic evoked urethral relaxations involves an increase in striated muscle tone. This appears to be an indirect result of smooth muscle relaxation and is mediated, at least in part, by a chlorisondamine-sensitive mechanism.

Augmentation of nitric oxide to treat detrusor-external sphincter dyssynergia in spinal cord injury

Detrusor-external sphincter dyssynergia (DSD) is a common cause of bladder outlet obstruction in men with spinal cord injuries, which if left untreated leads ultimately to renal failure. External sphincterotomy is currently the main treatment for DSD. However, obstruction persists in a substantial proportion of cases after this procedure. There is no effective drug treatment for DSD. Nitric oxide is an inhibitory neurotransmitter synthesised by nitric oxide synthase. Both animal and human studies suggest that nitric oxide mediates urethral sphincter relaxation. Nitric-oxide-synthase staining neurons have been identified in very high density in the urethral sphincters of a variety of animals and in human beings. Relaxation of the urethral sphincter is abolished by inhibitors of nitric oxide synthase and enhanced by nitric oxide donors. Mice with targeted deletion of the gene, for neuronal nitric oxide have urethral sphincters that do not relax in response to electrical stimulation. We hypothesise that augmentation of external sphincter nitric oxide could be an effective pharmacological treatment for DSD. Currently available nitric oxide donors such as glyceryl trinitrate or isosorbide mononitrate could be used to deliver nitric oxide to the urethral sphincter. The variable pharmacokinetics of these drugs combined with different modes of delivery (sublingual, buccal, or oral) could be used to achieve both short-term and long-term increases in concentrations of sphincter nitric oxide, thereby resulting in either acute or chronic lowering of urethral pressure. The safety and efficacy of this potential treatment for DSD needs to be established in clinical trials of men with spinal cord injures with DSD.

Phosphodiesterase 5 inhibitors and nitrergic transmission-from zaprinast to sildenafil

Phosphodiesterase 5 terminates the cellular actions of the second messenger molecule cyclic GMP; inhibitors of phosphodiesterase 5 will therefore increase and prolong the actions of endogenous substances that signal via the cyclic GMP pathway, including nitric oxide released as a neurotransmitter from nitrergic nerves. To date, the most widely used phosphodiesterase 5 inhibitors, zaprinast and sildenafil, have proved vital in the elucidation of the widespread role of cyclic GMP in nitrergic transmission and, specifically in the case of sildenafil, have provided a major breakthrough in the treatment of erectile dysfunction in men. Although still a matter of debate, early evidence indicates that sildenafil may also be of benefit in some forms of sexual dysfunction in women. The remarkable clinical success of sildenafil has prompted the search for further novel phosphodiesterase 5 inhibitors which might be used to enhance nitrergic function in other disease states.

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

Nitric oxide (NO)-mediated smooth muscle relaxation is mediated by cGMP through activation of cGMP-dependent protein kinase I (cGKI). We studied the importance of cGKI for lower urinary tract function in mice lacking the gene for cGKI (cGKI-/-) and in litter-matched wild-type mice (cGKI+/+) in vitro and in vivo. cGKI deficiency did not result in any changes in bladder gross morphology or weight. Urethral strips from cGKI-/- mice showed an impaired relaxant response to nerve-derived NO. The cGMP analog 8-bromo-cGMP (8-BrcGMP) and the NO-donor SIN-1 relaxed the wild-type urethra (50-60%) but had only marginal effects in the cGKI-deficient urethra. Bladder strips from cGKI-/- mice responded normally to electrical field stimulation and to carbachol but not to 8-BrcGMP. In vivo, the cGKI-deficient mice showed bladder hyperactivity characterized by decreased intercontraction intervals and nonvoiding bladder contractions. Loss of cGKI abolishes NO-cGMP-dependent relaxations of urethral smooth muscle and results in hyperactive voiding. These data suggest that certain voiding disturbances may be associated with impaired NO-cGKI signaling.

Nitric oxide-induced cGMP accumulation in the mouse bladder is not related to smooth muscle relaxation

The functional role of nitric oxide (NO) and the guanylate cyclase/cGMP second messenger system was investigated in the mouse bladder. Electrical field stimulation and the NO-donor 3-morpholino-sydnonimin hydrochloride (SIN-1) did not induce relaxation of the carbachol-precontracted bladder. However, sodium nitroprusside (10(-3) M) was found to enhance the contractile response to electrical field stimulation by 24+/-6% (n=8; P<0.05) without affecting the contractile response to carbachol. The enhancement of bladder contractility evoked by sodium nitroprusside was inhibited by the guanylate cyclase inhibitor 1H-[1,2, 4]oxadiazolo[4,3-a]quinoxalime-1-one (ODQ; 10(-6) M). Incubation of bladder strips with SIN-1 and sodium nitroprusside caused an increase in cGMP accumulation as measured by radioimmunoassay. Immunohistochemical studies showed cGMP-immunoreactivity in nerve fibres and in stromal cells, but not in smooth muscle bundles after exposure to NO-donors. The results show that NO-donors have no inhibitory effect on smooth muscle tone in the mouse bladder, but that NO may have a functional role as an excitatory neuromodulator. The targets of endogenous NO in the bladder may be the demonstrated cGMP-positive structures, i.e., nerves and stromal cells.

Localization of nitric oxide synthase and haemoxygenase, and functional effects of nitric oxide and carbon monoxide in the pig and human intravesical ureter

The distribution of nitric oxide synthase (NOS)-immunoreactive (IR) and haemoxygenase (HO)-IR nerves was investigated in the pig and human intravesical ureter (IVU). NOS activity was measured by monitoring the conversion of [3H]-arginine to [3H]-citrulline. Effects of NO and resulting changes in cyclic nucleotide concentrations were assessed in vitro. The effects of carbon monoxide (CO) on IVU motility was also tested. Immunohistochemistry revealed an abundant overall innervation of the IVU and numerous NOS-IR nerves. Nerve trunks were also found expressing immunoreactivity for HO-1, one of the enzymes synthetising CO. Similar profiles of nerve structures expressing immunoreactivities for NOS and tyrosine-hydroxylase (TH), as well as NOS and vasoactive intestinal peptide (VIP) were demonstrated. In the pig IVU, measurement of NOS activity revealed a moderate calcium-dependent catalytic activity, NO and the NO-donor SIN-1 reduced in a concentration-dependent manner serotonin-induced contractions of pig and human IVU, and the spontaneous contractions of pig IVU. In pig IVU strips precontracted with the thromboxane analogue U-46619, tetrodotoxin-sensitive relaxations were abolished by the NOS inhibitor NG-nitro-L-arginine. CO exerted no significant effect on spontaneous or induced contractions in the pig and human IVU. In precontracted strips of the pig and human IVU exposed to SIN-1 or NO, significant increases of cyclic GMP levels were measured in comparison to control preparations. The results suggest that the L-arginine/NO/cyclic GMP pathway may play a role in the regulation of the valve function in the uretero-vesical junction (UVJ). A role for CO in the UVJ has yet to be established.

Spontaneous photo-relaxation of urethral smooth muscle from sheep, pig and rat and its relationship with nitrergic neurotransmission

1. In the present work we have characterized the relaxant response induced by light stimulation (LS) in the lower urinary tract from sheep, pig and rat, establishing its relationship with nitrergic neurotransmission. 2. Urethral, but not detrusor, preparations showed pronounced photo-relaxation (PR) which declined progressively following repetitive LS. Sheep urethral PR was again restored either spontaneously or (to a greater extent) by exogenous nitric oxide (NO) addition and by electrical field stimulation (EFS) of intrinsic nitrergic nerves. 3. Greater NO generation was detected from sheep urethral than from detrusor homogenates following illumination. 4. Sheep urethral PR was inhibited by oxyhaemoglobin, but not by methaemoglobin, carboxy-PTIO, extracellular superoxide anion generators or superoxide dismutase. Guanylyl cyclase but not adenylyl cyclase activation mediates urethral relaxation to LS. 5. Urethral PR was more resistant to inhibition by L-thiocitrulline than EFS-induced responses, although this agent prevented PR restoration by high-frequency EFS. 6. Urethral PR was TTX insensitive and partially modified in high-K+ solutions. Cold storage for 24 h greatly impaired urethral PR, although it was restored by high-frequency EFS. 7. Repetitive exposure to LS, EFS or exogenous NO induced changes in the shape of the EFS-induced nitrergic relaxation, possibly by pre-synaptic mechanisms. 8. In conclusion, we suggest the presence of an endogenous, photo-labile, nitro-compound store in the urethra, which seems to be replenished by neural nitric oxide synthase activity, indicating a close functional relationship with the nitrergic neurotransmitter.

Relaxation of rabbit lower urinary tract smooth muscle by nitric oxide and carbon monoxide: modulation by hydrogen peroxide

Recent studies suggest that the body produces two gaseous messengers, nitric oxide (NO) and carbon monoxide (CO), both of which activate soluble guanylyl cyclase and thus modulate the activity of smooth muscle cells. In the present study, the effects of NO and CO on the smooth muscle of the lower urinary tract were compared. In addition, the modulation of tissue NO- and CO-induced relaxation by hydrogen peroxide was examined. NO, produced endogenously by electrical field stimulation (EFS) or applied exogenously as a solution, induced a concentration-dependent relaxation of rabbit cavernosal and urethral smooth muscle strips, but not of bladder tissues. The cavernosal tissue was found to be three times more sensitive to the actions of NO than the urethra. CO also induced relaxation of both tissue types, but with no apparent difference in sensitivity between the tissues. However, CO was much less potent than NO with respect to smooth muscle relaxation. The mechanism of action of the two mediators was cyclic guanosine monophosphate (cGMP)-dependent, as evidenced by enhanced formation of cGMP and inhibition of relaxation by the guanylyl cyclase inhibitor, oxadiazoloquinoxaline-1-one (ODQ.) The data suggests that NO is the dominant messenger in these tissues, but does not exclude a role for CO. In the presence of hydrogen peroxide, the relaxation responses induced by both NO and CO were significantly increased, regardless of tissue type. The mechanism for this effect is unclear, but evidence points to a requirement for the activation of guanylyl cyclase and enhanced formation of cGMP, since potentiation by the peroxide was blocked by a specific guanylyl cyclase inhibitor. We suggest that H(2)O(2) may play a positive role in the amplification or NO and CO-mediated responses.

Potential role of endothelin and nitric oxide in physiology and pathophysiology of the lower urinary tract

Endothelium-derived vasoactive mediators (endothelin-1 with its vasoconstrictive and mitogenic properties and nitric oxide with its vasodilatory and antiproliferative properties) play an important role in the regulation of vascular smooth muscle tone and cellular proliferation. Several recent studies have now demonstrated the presence of these vasoactive agents in the urinary tract where they are thought to play a prominent role in urinary tract physiology and disease. This article reviews the synthesis, localisation and actions of endothelin and nitric oxide in the lower urinary tract and examines the possible role of these mediators in disease.

The nitric oxide pathway in pig isolated calyceal smooth muscle

In pig and humans, whose kidneys have a multi-calyceal collecting system, the initiation of ureteral peristalsis takes place in the renal calyces. In the pig and human ureter, recent evidence suggests that nitric oxide (NO) is an inhibitory mediator that may be involved in the regulation of peristalsis. This study was designed to assess whether the NO synthase/NO/cyclic GMP pathway modulates the motility of pig isolated calyceal smooth muscle. Immunohistochemistry revealed a moderate overall innervation of the smooth muscle layer, and no neuronal or inducible NO synthase (NOS) immunoreactivities. Endothelial NOS immunoreactivities were observed in the urothelium and vascular endothelium, and numerous cyclic GMP-immunoreactive (-IR) calyceal smooth muscle cells were found. As measured by monitoring the conversion of L-arginine to L-citrulline, Ca(2+)-dependent NOS activity was moderate. Assessment of functional effects was performed in tissue baths and showed that NO and SIN-1 decreased spontaneous and induced contractions of isolated preparations in a concentration-dependent manner. In strips exposed to NO, there was a 10-fold increase of the cyclic GMP levels compared with control preparations (P < 0.01). It is concluded that a non-neuronal NOS/NO/cyclic GMP pathway is present in pig calyces, where it may influence motility. The demonstration of cyclic GMP-IR smooth muscle cells suggests that NO acts directly on these cells. This NOS/NO/cyclic GMP pathway may be a target for drugs inhibiting peristalsis of mammalian upper urinary tract. Neurourol. Urodynam. 18:673-685, 1999.

Inhibitory innervation of the guinea-pig urethra; roles of CO, NO and VIP

The inhibitory innervation of guinea-pig urethral smooth muscle was investigated histochemically and functionally. The distribution of immunoreactivities to haem oxygenases (HO), neuronal NO synthase (nNOS), and vasoactive intestinal polypeptide (VIP) was studied, and the functional effects of the corresponding putative transmitters, CO, NO, and VIP, were assessed. HO-2 immunoreactivity was found in all nerve cell bodies of intramural ganglia, localized between smooth muscle bundles in the detrusor, bladder base and proximal urethra. About 70% of the ganglionic cell bodies were also NOS-immunoreactive (IR), whereas a minor part was VIP-IR. Some ganglion cells exhibiting tyrosine hydroxylase (TH) activity were demonstrated. Rich numbers of NOS-IR varicose nerve terminals could be found innervating the smooth muscle of the urethra, whereas VIP-IR terminals were less numerous. A rich number of TH-IR terminals were observed. The bladder showed a similar distribution of nerves, although only a few number of TH-IR nerves could be found. In bladder preparations exposed to sodium nitroprusside, cGMP-IR cells could be seen, forming an interconnecting network with long spindle-shaped processes. The cGMP-IR cells were especially abundant in the outer smooth muscle layers of the bladder, but less numerous in the urethra. In urethral strip preparations, electrical field stimulation evoked long-lasting frequency-dependent relaxations. The relaxations were not inhibited by the NO-synthesis inhibitor, L-NOARG, or enhanced by the NO-precursor, L-arginine. The haem precursor, 5-aminolevulinic acid (5-ALA), or the inhibitor of guanylate cyclase, ODQ, did not affect the urethral relaxations. Exogenously applied NO, SIN-1, and VIP relaxed the preparations by approximately 50%, whereas the relaxation evoked by exogenous CO was minor. These results suggest that CO probably is not involved in non-adrenergic, non-cholinergic inhibitory control of the guinea-pig urethra, where a non-NO/cGMP mediated relaxation seems to be predominant.

ATP and vasoactive intestinal polypeptide relaxant responses in hamster isolated proximal urethra

1. Nitric oxide (NO) is known from previous studies to be the principle transmitter in NANC inhibitory nerves supplying the hamster urethra. However, the identity of the cotransmitter(s) responsible for the responses remaining following block with L-NG-nitroarginine methyl ester (L-NAME) is not known. 2. Electrical field stimulation (EFS) of circular strips of hamster proximal urethra precontracted with arginine vasopressin (AVP 10(-8) M), and in the presence of phentolamine (10(-6) M), propranolol (10(-6) M) and atropine (10(-6) M), caused frequency-dependent relaxation, which was attenuated by suramin (10(-4) M) and reactive blue 2 (RB2; 2 x 10(-4) M), but not by pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS; 10(-4) M), alpha-chymotrypsin (10-50 u ml(-1)) or by the vasoactive intestinal polypeptide (VIP) antagonist, [Lys1, Pro2,5, Arg3,4, Tyr6]-VIP, (5 x 10(-7)-10(-6) M). In the presence of indomethacin (10(-6) M) frequency-dependent relaxations to EFS were enhanced, particularly at the lower frequencies of stimulation. EFS-induced relaxation was blocked by tetrodotoxin (10(-6) M), indicating its neurogenic origin. 3. Exogenous ATP (10(-7)-10(-3) M) produced concentration-related relaxations which were attenuated by the P2-purinoceptor antagonists suramin (10(-4) M) and RB2 (2 x 10(-4) M) but not by PPADS (10(-4) M). ATP-induced relaxations were also reduced significantly by indomethacin (10(-6) M). The inhibitory responses to ATP were urothelium- and NO-independent, since they were not affected by either removal of urothelium or by L-NAME (10(-4) M). 4. Exogenous VIP (10(-9)-10(-7) M) induced concentration-related relaxations which were not affected by urothelium removal, L-NAME (10(-4) M), alpha-chymotrypsin (10-50 u ml(-1)) or by [Lys1, Pro2,5, Arg3,4, Tyr6]-VIP (3 x 10(-7)-10(-6) M). Nevertheless, suramin (10(-4) M) and RB2 (2 x 10(-4) M) but not PPADS (10(-4) M) antagonized the VIP-induced relaxant responses. Calcitonin gene-related peptide (CGRP: 10(-9)-10(-7) M) was devoid of any effect or only elicited a small relaxant response in AVP-precontracted strips. 5. Exogenous prostaglandin E2 (PGE2; 10(-9)-3 x 10(-6) M) and the NO donor, sodium nitroprusside (SNP; 10(-8)-3 x 10(-5) M) elicited concentration-related relaxations on the hamster proximal urethra which were not attenuated by suramin (10(-4) M), RB2 (2 x 10(-4) M), or by PPADS (10(-4) M), indicating a specific inhibitory effect of the antagonists used. 6. In summary, these results are consistent with the view that ATP is an inhibitory transmitter released from inhibitory nerves supplying the NANC relaxation of hamster proximal urethra. The relaxant effect of ATP is NO- and urothelium-independent. The present study did not demonstrate whether VIP is released from parasympathetic nerves during EFS, since both alpha-chymotrypsin and [Lys1, Pro2,5, Arg3,4, Tyr6]-VIP were ineffective on neurogenic responses.

Mediators and mechanisms of relaxation in rabbit urethral smooth muscle

1. Electrophysiological and mechanical experiments were performed to investigate whether the nitric oxide (NO)-mediated relaxation of rabbit urethral smooth muscle is associated with a hyperpolarization of the membrane potential. In addition, a possible role for vasoactive intestinal peptide (VIP) and carbon monoxide (CO) as relaxant agents in rabbit urethra was investigated. 2. Immunohistochemical experiments were performed to characterize the NO-synthase (NOS) and VIP innervation. Possible target cells for NO were studied by using antisera against cyclic GMP. The cyclic GMP-immunoreactivity was investigated on tissues pretreated with 1 mM IBMX, 0.1 mM zaprinast and 1 mM sodium nitroprusside. 3. Intracellular recordings of the membrane potential in the circular smooth muscle layer revealed two types of spontaneous depolarizations, slow waves with a duration of 3-4 s and an amplitude of 30-40 mV, and faster (0.5-1 s), more irregular depolarizations with an amplitude of 5-15 mV. The resting membrane potential was 39 +/- 1 mV (n = 12). Application of NO (30 microM), CO (30 microM) or VIP (1 microM) did not change the resting membrane potential. 4. Both NO (1-100 microM) and VIP (1 nM-1 microM) produced concentration-dependent relaxations amounting to 87 +/- 4% and 97 +/- 2% (n = 6), respectively. The relaxant effect of CO (1-30 microM) amounted to 27 +/- 4% (n = 5) at the highest concentration used. 5. Immunohistochemical experiments revealed a rich supply of NOS-immunoreactive nerve fibres in the smooth muscle layers. Numerous spinous cyclic GMP-immunoreactive cells were found interspersed between the smooth muscle bundles, mainly localized in the outer layer. These cells had long processes forming a network surrounding the smooth muscle bundles. VIP-immunoreactivity was sparse in comparison to NOS-immunoreactive nerves. 6. The rich supply of NOS-immunoreactive nerve fibres supports the view that NO is an important NANC-mediator in the rabbit urethra. In contrast to several other tissues, the relaxant effect of NO in the rabbit urethra does not seem to be mediated by hyperpolarization. The network of cyclic GMP-immunoreactive cells may constitute target cells for NO, but their function remains to be established.

Effect of long-term oral L-arginine on the nitric oxide synthase pathway in the urine from patients with interstitial cystitis

PURPOSE

We attempted to determine whether oral L-arginine, the substrate for nitric oxide synthase, increases nitric oxide synthase activity and cyclic guanosine monophosphate (cGMP) levels in the urine from interstitial cystitis patients. Nitric oxide and cGMP are decreased in urine from interstitial cystitis patients and both induce smooth muscle relaxation and immunological responses. Increasing urinary nitric oxide and cGMP may ameliorate interstitial cystitis symptoms.

MATERIALS AND METHODS

Eight patients with interstitial cystitis were given L-arginine (1,500 mg. a day) orally for 6 months. Before and during treatment nitric oxide synthase activity and inducible nitric oxide synthase protein, cGMP, nitrate plus nitrite and interleukin 8 (IL-8) levels were measured in urine.

RESULTS

After 2 weeks to 1 month of oral L-arginine treatment, urinary levels of nitric oxide synthase related enzymes and products increased significantly, while levels of the cytokine IL-8 were not changed significantly. IL-8 was significantly elevated in interstitial cystitis patients with leukocyte esterase positive urine.

CONCLUSIONS

Long-term oral administration of L-arginine increases nitric oxide related enzymes and metabolites in the urine of patients with interstitial cystitis, which is associated with a decrease in interstitial cystitis related symptoms.

Carbon monoxide-induced relaxation and distribution of haem oxygenase isoenzymes in the pig urethra and lower oesophagogastric junction

1. The distribution of the carbon monoxide (CO) producing enzymes haem oxygenase (HO)-1 and -2 was studied by immunohistochemistry in the pig's lower urinary tract, including bladder extramural arteries, and the oesophagogastric junction (OGJ). In isolated smooth muscle from the urethra and the OGJ, the mechanisms for CO-induced relaxations were characterized by measurement of cyclic nucleotide levels and by responses to the guanylate cyclase inhibitor methylene blue and some K+ channel inhibitors. 2. HO-2 immunoreactivity was observed in coarse nerve trunks within the smooth muscle of the urethra and OGJ, and in nerve cell bodies of the enteric plexuses of the OGJ. Furthermore, the vascular endothelium of the intramural vessels of the urethra, bladder and OGJ, and the extramural vessels of the bladder, displayed HO-2 immunoreactivity. Two different antisera against HO-1 were used, but only one displayed immunoreactivity in neuronal structures. HO-1 immunoreactivity, as displayed by this antiserum, was seen in nerve cells, coarse nerve trunks and varicose nerve fibres in the smooth muscle of the urethra and OGJ. Some HO-2 and/or HO-1 (as displayed by both HO-1 antisera) immunoreactive cells with a non-neuronal appearance were observed within the smooth muscle of the OGJ, bladder and urethra. 3. In the urethral preparations, exogenously applied CO (72 microM) evoked a relaxation amounting to 76 +/- 6%. The relaxation was associated with an increase in cyclic GMP, but not cyclic AMP, content. CO-evoked relaxations were not significantly reduced by treatment with methylene blue, or by inhibitors of voltage-dependent (4-aminopyridine), high (iberiotoxin, charybdotoxin) and low (apamin) conductance Ca(2+)-activated, and ATP-sensitive (glibenclamide) K+ channels. Bladder strips, and ring preparations from the extramural arteries of the bladder, did not respond to exogenously administered CO (12-72 microM). 4. In the OGJ, exogenously applied CO evoked a relaxation of 86 +/- 6%, which was associated with an increase in cyclic GMP, but not cyclic AMP, content. Treatment with 30 microM methylene blue raised the spontaneously developed muscle tone, and reduced the maximum relaxation evoked by CO to 33 +/- 9%. Addition of 4-aminopyridine, apamin, glibenclamide, iberiotoxin, charybdotoxin or glibenclamide had no effect on the relaxations. 4-aminopyridine (0.1-1 mM), iberiotoxin (0.1 microM) and charybdotoxin (0.1 microM) increased the spontaneously developed tone, and a combination of charybdotoxin and apamin reduced CO-induced (24 microM CO) relaxations. 5. The present findings demonstrate the presence of HO in both neuronal and non-neuronal cells in the pig OGJ and lower urinary tract. CO produces relaxation of the smooth muscle in the OGJ and urethra, associated with a small increase in cyclic GMP concentration in both regions. Relaxations evoked by CO in the urethra do not seem to involve voltage-dependent, low and high conductance, or ATP-dependent K+ channels. However, in the OGJ relaxations evoked by CO can be attenuated by methylene blue and a combination of charybdotoxin and apamin.

A pharmacological and histochemical study of hamster urethra and the role of urothelium

1. Electrical field stimulation (EFS) of circular strips of hamster proximal urethra caused frequency-dependent relaxations at raised tone. Phentolamine (10(-6) M), propranolol (10(-6) M) and atropine (10(-6) M) were present throughout the experiment. Neurogenic relaxation was attenuated by L-NG-nitroarginine methyl ester (L-NAME) (10(-4) M), was restored by L-arginine (3 x 10(-3) M) but not by D-arginine (3 x 10(-3) M) and completely blocked by tetrodotoxin (10(-6) M). Neurogenic relaxation was also reduced by suramin (10(-4) M) and totally blocked by suramin together with L-NAME. Strips of hamster urethra devoid of urothelium showed little, if any, relaxant response to EFS. 2. An immunohistochemical study showed nitric oxide synthase-immunoreactive nerves in the smooth muscle layers and in the lamina propria, just beneath the urothelium, but no nitric oxide synthase (NOS) staining in the urothelial layer. 3. Noradrenaline elicited a significantly greater contraction in strips without urothelium than in control strips. L-NAME (10(-4) M) did not affect noradrenaline-induced contraction in both control and urothelium-free strips. The contractile response to acetylcholine was not dependent on the presence or absence of urothelium. Nevertheless the response induced by exogenous acetylcholine (10(-3) M) was increased by L-NAME (10(-4) M), both in intact and in urothelium-free strips. 4. Prostaglandin E2 (10(-8)-5 x 10(-6) M) and 2-methyl-thio-ATP (10(-9)-10(-5) M) relaxed proximal urethra. Suramin (10(-4) M) significantly inhibited the relaxation induced by 2-methyl-thio-ATP. The amplitude of these responses was not significantly different between intact and urothelium-free strips and was not blocked by L-NAME (10(-4) M). 5. These results suggest that nitric oxide (NO) is the principal transmitter involved in the non-adrenergic, non-cholinergic (NANC) relaxation of hamster proximal urethra possibly together with another inhibitory transmitter released from nerves. NO can be released from nerves located in the circular smooth muscle layer and in the lamina propria rather than in the urothelium. The reduced neurogenic relaxation in urothelium-free preparations suggests that a NO-dependent inhibitory factor is released from the urothelium. In addition, ATP and prostaglandin E2 may be involved, together with NO, in the urethra during micturition.

Distribution of nitric oxide synthase-immunoreactive nerves and identification of the cellular targets of nitric oxide in guinea-pig and human urinary bladder by cGMP immunohistochemistry

The distribution of nerves with the potential to synthesize nitric oxide was examined within the urinary bladder and proximal urethra of humans and guinea-pigs, using an antibody to nitric oxide synthase. Further experiments identified cells in which cGMP-immunoreactivity was induced following exposure to the nitric oxide donor, sodium nitroprusside. These cells represent the potential physiological targets of neuronally released nitric oxide, since activation of soluble guanylate cyclase, and a consequent rise in intracellular cGMP, mediate many of the effects of this transmitter. Nitric oxide synthase-immunoreactivity was widely distributed in the lower urinary tract. In guinea-pigs, 50-68% of all intrinsic vesical neurons expressed nitric oxide synthase-immunoreactivity, while in humans 72-96% of neurons in the wall of the bladder contained nitric oxide synthase. In both humans and guinea-pigs, varicose nitric oxide synthase-immunoreactive nerve terminals provided a moderate innervation to the detrusor muscle of the bladder body, and a denser innervation to the urethral muscle. Immunoreactive nerves also projected to the subepithelium and around blood vessels, but were rarely observed encircling intramural vesical ganglia. Following stimulation with sodium nitroprusside, smooth muscle cells of the urethra expressed strong cGMP-immunoreactivity, but detrusor muscle cells remained uniformly negative. Although the detrusor muscle fibres did not express cGMP, numerous interstitial cells throughout the bladder body demonstrated an intense induction of cGMP-immunoreactivity by sodium nitroprusside. These cells had long dendritic processes extending parallel to the smooth muscle fibres, and contained vimentin, an intermediate filament expressed by cells of mesenchymal origin. Other cell types in which sodium nitroprusside exposure induced cGMP-immunoreactivity were the uroepithelial cells, vascular smooth muscle cells and pericytes, and a small number of varicose nerve terminals. In the guinea-pig, a minor proportion (less than 10%) of intrinsic neurons in the wall of the bladder also expressed cGMP. No intrinsic neurons were observed in specimens of human bladder processed for cGMP immunohistochemistry. The results provide anatomical evidence that nitric oxide may function as a neurotransmitter in the lower urinary tract. Although nerves with the capacity to produce nitric oxide supply both the detrusor muscle and the urethra, distinct regional differences exist in the effects of nitric oxide on the induction of cGMP. If the nitric oxide-mediated induction of cGMP is a reliable indicator of the physiological responsiveness of a cell to nitric oxide, then smooth muscle cells appear to be the predominant targets of nitric oxide in the urethra, while in the bladder body, interstitial cells may serve this role. These findings support previous studies which have implicated nitric oxide as an inhibitory transmitter involved in the relaxation of the bladder neck. Our experiments further indicate that a number of cell types within the lower urinary tract could potentially mediate the effects of endogenously released nitric oxide.

Effects of various phosphodiesterase-inhibitors, forskolin, and sodium nitroprusside on porcine detrusor smooth muscle tonic responses to muscarinergic stimulation and cyclic nucleotide levels in vitro

The cyclic nucleotides cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) are second messengers involved in the regulation of contractility in various smooth muscle organs including detrusor smooth muscle. They are synthesized by activation of adenylate and guanylate cyclases, respectively, and inactivated by phosphodiesterases (PDEs). In order to delineate the intracellular regulation of porcine detrusor contractility by cyclic nucleotides and phosphodiesterases, functional organ bath studies and determinations of intracellular cyclic nucleotide contents were performed after incubation of porcine detrusor strips with forskolin (adenylate cyclase activator), sodium nitroprusside (guanylate cyclase activator), and various phosphodiesterase-inhibitors. Significant relaxant responses were achieved only by forskolin, the nonspecific phosphodiesterase-inhibitor papaverine, and the phosphodiesterase 1-inhibitor vinpocetine (62.4 +/- 5.6%, 73 +/- 4.3%, and 53 +/- 7.9%, respectively). Sodium nitroprusside and the selective PDE-inhibitors milrinone, rolipram, zaprinast, and dipyridamole were significantly less efficacious (26.9 +/- 3.9%, 15.5 +/- 3.8%, 15.3 +/- 3.0%, 13 +/- 4.0%, and 13.2 +/- 2.1%, respectively). Forskolin, papaverine, and vinpocetine elevated intracellular cAMP concentrations (7.3-, 1.9-, and 1.7-fold increase at 100 microM, respectively), whereas the other substances failed to enhance cAMP levels. cGMP levels were only increased by sodium nitroprusside (7.8-fold). The adenylate cyclase-cAMP system seems to be the more important signal transduction system involved in the relaxation of carbachol induced smooth muscle tone of the porcine detrusor. The role of the guanylate cyclase-cGMP system is less clear. In addition, the calcium/calmodulin-stimulated PDE I seems to be of major functional importance in regulating cAMP hydrolysis in the porcine detrusor smooth muscle in vitro.

Effects of KRN2391, a novel vasodilator acting as a nitrate and a K+ channel opener, on the rabbit lower urinary tract

1. The relaxant effect of KRN2391, suggested to act both as a nitrate and a K+ channel opener, was investigated in the rabbit lower urinary tract and compared with the effects of the NO-donor SIN-1 and the K+ channel opener levcromakalim. 2. KRN2391 10(-4) M was able to relax precontracted urethral preparations by 87 +/- 4%. Corresponding values for levcromakalim 10(-4) M and SIN-1 10(-4) M were 58 +/- 8% and 103 +/- 2%, respectively. The -logEC50 values for KRN2391, SIN-1 and levcromakalim were 6.0 +/- 0.1, 4.9 +/- 0.2 and 5.8 +/- 0.2. The relaxant effect of KRN2391 on the bladder was small (29 +/- 3%). 3. The levels of cyclic GMP in the urethral preparations were significantly increased after administration of KRN2391 10(-4) M and SIN-1 10(-4) M, but not after levcromakalim 10(-4) M, the levels measured being 9.9 +/- 2.2, 20.9 +/- 5.1, and 5.2 +/- 1.0, compared to the control value, 3.7 +/- 0.5 pmol/mg protein. The levels of cyclic AMP were, however, not changed. 4. The relaxations, caused by KRN2391 in the urethral preparations, were accompanied by a hyperpolarization (14 +/- 4 mV) of the membrane potential. 5. Methylene blue 3 x 10(-5) M and glibenclamide 10(-5) M significantly reduced the relaxant effect of KRN2391 in the urethral smooth muscle. 6. We suggest that in the rabbit lower urinary tract, KRN2391 acts mainly as an NO-donor.

Factors involved in the relaxation of female pig urethra evoked by electrical field stimulation

1. Non-adrenergic, non-cholinergic (NANC) relaxations induced by electrical field stimulation (EFS) were studied in pig isolated urethra. The mechanism for relaxation was characterized by measurement of cyclic nucleotides and by study of involvement of different subsets of voltage-operated calcium channels (VOCCs). 2. EFS evoked frequency-dependent and tetrodotoxin-sensitive relaxations in the presence of propranolol (1 microM), phentolamine (1 microM) and scopolamine (1 microM). At low frequencies (< 12 Hz), relaxations were rapid, whereas at high (> 12 Hz) frequencies distinct biphasic relaxations were evoked. The latter consisted of a rapidly developing first phase followed by a more long-lasting second phase. 3. Treatment with the NO-synthesis inhibitor NG-nitro-L-arginine (L-NOARG; 0.3 mM) inhibited relaxations at low frequencies of stimulation. At high frequencies (> 12 Hz) only the first relaxation phase was affected. 4. Measurement of cyclic nucleotides in preparations subjected to continuous nerve-stimulation, revealed an increase in guanosine 3':5'-cyclic monophosphate (cyclic GMP) levels from 1.3 +/- 0.3 to 3.0 +/- 0.4 pmol mg-1 protein (P < 0.01). In the presence of L-NOARG, there was a significant decrease in cyclic GMP content to control. However, there was no increase in cyclic GMP content in response to EFS. Levels of cyclic AMP remained unchanged following EFS. 5. Treatment with the N-type VOCC-inhibitor, omega-conotoxin GVIA (0.1 microM) reduced NO-dependent relaxations, the effect being most pronounced at low frequencies (1-4 Hz) of stimulation. The NO independent second phase of the relaxation, studied in the presence of L-NOARG (0.3 mM) at 16-30 Hz, was however markedly reduced or abolished by omega-conotoxin GVIA. omega-Conotoxin MVIIC (1 microM)or omega-agatoxin IVA (30 nM) had no effect on electrically evoked relaxations.6. These results suggest that NANC-nerve derived urethral relaxation in the pig consists of two apparently independent components. One is mediated by NO and associated with an increase in cyclic GMP content. The other mediator is unknown and produces relaxations not associated with changes in levels of cyclic nucleotides. The release of this mediator seems to involve the N-type VOCC, since the relaxation was markedly reduced or abolished by omega-conotoxin GVIA.

Nitric oxide synthase and nitric oxide-mediated effects in lower urinary tract smooth muscles

In the lower urinary tract smooth muscles, both excitatory and inhibitory non-adrenergic, non-cholinergic (NANC) nerves and neurotransmission can be demonstrated. An inhibitory, relaxation-mediating system may serve not only the detrusor, the trigone, and the bladder neck/urethra, but may also be of importance for their integrated function. Available data suggest that nitric oxide synthase (NOS) is localized in nerve fibres of the lower urinary tract, preferably in the outflow region, and evidence has accumulated that L-arginine-derived nitric oxide (NO) is responsible for the main part of the inhibitory NANC response. Coinciding localization of NOS positive nerves with nerves expressing acetylcholine esterase, vasoactive intestinal peptide, and neuropeptide Y, suggests that NO may have a role both as a directly acting transmitter and as a modulator of efferent neurotransmission. In addition, NO may be involved in afferent neurotransmission. Theoretically, NO released from nerves in the detrusor, could be one factor keeping the bladder relaxed during filling. However, the detrusor has a low sensitivity to NO and agents acting via cyclic GMP, which makes it less likely that NO has a role as a relaxant neurotransmitter. This does not exclude that NO may modulate the effects of other transmitters, or that it has an afferent function. NO effectively relaxes isolated smooth muscle preparations from the outflow region, suggesting that it may be involved in the decrease in intraurethral pressure associated with normal micturition, and with the excessive urethral pressure variations ("unstable urethra"), which may be associated with certain voiding disturbances in women.(ABSTRACT TRUNCATED AT 250 WORDS)