Nitric oxide-mediated suppression of detrusor overactivity by arginase inhibitor in rats with chronic spinal cord injury

Targeting neurotrophin and nitric oxide signaling to treat spinal cord injury and associated neurogenic bladder overactivity

Purpose or the research

Nearly 300,000 people are affected by spinal cord injury (SCI) with approximately 18,000 new cases annually, according to the National SCI Statistics Center. SCI affects physical mobility and impairs the function of multiple internal organs to cause lower urinary tract (LUT) dysfunctions manifesting as detrusor sphincter dyssynergia (DSD) and neurogenic detrusor overactivity (NDO) with detrimental consequences to the quality of life and increased morbidity. Multiple lines of evidence now support time dependent evolution of the complex SCI pathology which requires a multipronged treatment approach of immediate, specialized care after spinal cord trauma bookended by physical rehabilitation to improve the clinical outcomes. Instead of one size fits all treatment approach, we propose adaptive drug treatment to counter the time dependent evolution of SCI pathology, with three small molecule drugs with distinctive sites of action for the recovery of multiple functions.

Principal results

Our findings demonstrate the improvement in the recovery of hindlimb mobility and bladder function of spinal cord contused mice following administration of small molecules targeting neurotrophin receptors, LM11A-31 and LM22B-10. While LM11A-31 reduced the cell death in the spinal cord, LM22B-10 promoted cell survival and axonal growth. Moreover, the soluble guanylate cyclase (sGC) activator, cinaciguat, enhanced the revascularization of the SCI injury site to promote vessel formation, dilation, and increased perfusion.

Major conclusions

Our adaptive three drug cocktail targets different stages of SCI and LUTD pathology: neuroprotective effect of LM11A-31 retards the cell death that occurs in the early stages of SCI; and LM22B-10 and cinaciguat promote neural remodeling and reperfusion at later stages to repair spinal cord scarring, DSD and NDO. LM11A-31 and cinaciguat have passed phase I and IIa clinical trials and possess significant potential for accelerated clinical testing in SCI/LUTD patients.

Gabapentin add-on therapy for patients with spinal cord injury associated neurogenic overactive detrusors that are unresponsive to combined anticholinergic and beta-3 adrenergic therapy

Introduction

Spinal cord injury is a major cause of lifelong morbidity and functional micturition problems. Some patients are refractory to the available therapeutics, even when used in combination. In this paper we report our results of using gabapentin as an add-on treatment in refractory overactive detrusor cases secondary to spinal cord injury.

Material and methods

A total of 27 patients who had a spinal cord injury between the levels of the second thoracic and fourth lumbar vertebrae and had an overactive detrusor in urodynamic studies were included in this retrospective study. The patients were selected due to the fact that they also had not responded to a combination of an anticholinergic and mirabegron and had neuropathic pain. Gabapentin treatment was added to the previous therapy. Demographics, previous treatments, chronic conditions, urodynamic findings, clinical and urodynamic responses are reported in this paper.

Results

We observed a response to treatment in the urodynamic studies of 11 patients (40.17%), in terms of decreased detrusor contractions, maximal detrusor pressure, and the number of incontinence episodes. Sixteen patients did not respond to the gabapentin add-on therapy and were referred for Botulinum toxin injections to the bladder.

Conclusions

Gabapentin add-on therapy can be considered as a third or further option, before Botulinum toxin injection, for patients with neurogenic overactive detrusor who did not respond to the combination of anticholinergics and mirabegron. The approved usage of gabapentin for neurogenic pain justifies its usage in this area. In our selected patient group, who had not responded to the combination therapy, we observed a clinical benefit in one-third of the patients.

Recommendations for evaluation of bladder and bowel function in pre-clinical spinal cord injury research

Objective: In order to encourage the inclusion of bladder and bowel outcome measures in preclinical spinal cord injury (SCI) research, this paper identifies and categorizes 1) fundamental, 2) recommended, 3) supplemental and 4) exploratory sets of outcome measures for pre-clinical assessment of bladder and bowel function with broad applicability to animal models of SCI.Methods: Drawing upon the collective research experience of autonomic physiologists and informed in consultation with clinical experts, a critical assessment of currently available bladder and bowel outcome measures (histological, biochemical, in vivo functional, ex vivo physiological and electrophysiological tests) was made to identify the strengths, deficiencies and ease of inclusion for future studies of experimental SCI.Results: Based upon pre-established criteria generated by the Neurogenic Bladder and Bowel Working Group that included history of use in experimental settings, citations in the literature by multiple independent groups, ease of general use, reproducibility and sensitivity to change, three fundamental measures each for bladder and bowel assessments were identified. Briefly defined, these assessments centered upon tissue morphology, voiding efficiency/volume and smooth muscle-mediated pressure studies. Additional assessment measures were categorized as recommended, supplemental or exploratory based upon the balance between technical requirements and potential mechanistic insights to be gained by the study.Conclusion: Several fundamental assessments share reasonable levels of technical and material investment, including some that could assess bladder and bowel function non-invasively and simultaneously. Such measures used more inclusively across SCI studies would advance progress in this high priority area. When complemented with a few additional investigator-selected study-relevant supplemental measures, they are highly recommended for research programs investigating the efficacy of therapeutic interventions in preclinical animal models of SCI that have a bladder and/or bowel focus.

Ocimum gratissimum Linn. Leaves reduce the key enzymes activities relevant to erectile dysfunction in isolated penile and testicular tissues of rats

BACKGROUND

Ocimum gratissimum L. is a medicinal plant widely grown in tropical and subtropical regions with the leaf decoction usually taken in folk medicine to enhance erectile performance in men although the probable mechanism of actions remains undetermined. This study examined the inhibitory potentials of Ocimum gratissimum leaves on some key enzymes associated with erectile dysfunction in penile and testicular tissues of the rat.

METHODS

Inhibitory effect of aqueous extract (1:10 w/v) of O. gratissimum leaves on the activities of phosphodiesterase-5 (PDE-5), arginase, angiotensin I -converting enzyme (ACE), and acetylcholinesterase (AChE) in penile and testicular tissues were assessed. Also, the extract was investigated for ferric reducing antioxidant property(FRAP) and 1,1-diphenyl-2-picryl-hydrazil (DPPH) radical scavenging abilities.

RESULTS

The extract showed higher PDE-5 (IC₅₀ = 43.19 μg/mL), ACE (IC₅₀ = 44.23 μg/mL), AChE (IC₅₀ = 55.51 μg/mL) and arginase (IC₅₀ = 46.12 μg/mL) inhibitory activity in the penile tissue than PDE-5 (IC₅₀ = 44.67 μg/mL), ACE (IC₅₀ = 53.99 μg/mL), AChE (IC₅₀ = 60.03 μg/mL) and arginase (IC₅₀ = 49.12 μg/mL) inhibitory activity in the testicular tissue homogenate. Furthermore, the extract scavenged free radicals and in a dose-dependent manner.

CONCLUSION

The enzyme activities displayed might be associated with the bioactive compounds present in the extract which could possibly explain its use in the management of erectile dysfunction (ED).

Pharmacokinetics and Pharmacodynamics of Promising Arginase Inhibitors

Up-regulation of arginase activity in several chronic disease conditions, including cancer and hypertension, may suggest new targets for treatment. Recently, the number of new arginase inhibitors with promising therapeutic effects for asthma, cancer, hypertension, diabetes mellitus, and erectile dysfunction has shown a remarkable increase. Arginase inhibitors may be chemical substances, such as boron-based amino acid derivatives, α-difluoromethylornithine (DMFO), and Nω-hydroxy-nor-L-arginine (nor-NOHA) or, of plant origin such as sauchinone, salvianolic acid B (SAB), piceatannol-3-O-β-D-glucopyranoside (PG) and obacunone. Despite their promising therapeutic potential, little is known about pharmacokinetics and pharmacodynamics of some of these agents. Several studies were conducted in different animal species and in vitro systems and reported significant differences in pharmacokinetics and pharmacodynamics of arginase inhibitors. Therefore, extra caution should be considered before extrapolating these studies to human. Physicochemical and pharmacokinetic profiles of some effective arginase inhibitors make it challenging to formulate stable and effective formulation. In this article, existing literature on the pharmacokinetics and pharmacodynamics of arginase inhibitors were reviewed and compared together with emphasis on possible drug interactions and solutions to overcome pharmacokinetics challenges and shortage of arginase inhibitors in clinical practice.

Effects of daily tadalafil on lower urinary tract symptoms in young men with multiple sclerosis and erectile dysfunction: a pilot study

PURPOSE

Men affected by multiple sclerosis often experience neurogenic overactive bladder (OAB), lower urinary tract symptoms and erectile dysfunction (ED). The aim of the study was to investigate modifications of urinary and sexual functions after administration of daily tadalafil (TAD) 5 mg.

METHODS

Twenty men were enrolled in a single-blind, 4-week prospective study while 10 men without treatment served as controls. Primary outcomes were changes from baseline of International Prostate Symptom (IPSS), OAB questionnaire (OAB-q-short form) and International Index of Erectile Function (IIEF-5) scores. To evaluate the influence of bladder filling on somatic reflexes, we studied variations of the H-reflex evoked by electrical stimuli applied to the tibial nerve at the popliteal fossa and recorded from the soleus muscle. Also testosterone/estradiol (T/E) ratio was measured before and after treatment.

RESULTS

In TAD group, an improvement in IPSS (p < 0.001), OAB-q (p < 0.001) and IIEF-5 (p < 0.001) scores was found. Also, an increase in Q _max (p < 0.01) and T/E ratio (p < 0.01) was found with a concomitant reduction in post-void residual volume (p < 0.001) without any changes in the H-reflex.

CONCLUSIONS

The study demonstrates for the first time that daily TAD in patients with multiple sclerosis improves storage symptoms, post-void residual volume, steroid hormone pattern and ED without urodynamic changes.

Identification of temporal genes involved in the mechanisms of spinal cord injury

OBJECTIVES

As a high-cost neurological disability, spinal cord injury (SCI) can result in permanent paralysis and loss of sensation. To identify the temporal genes involved in the pathogenesis of SCI, we analysed the expression profile of GSE45006.

METHODS

GSE45006 was downloaded from Gene Expression Omnibus, including 20 SCI samples (samples at 1 day, 3 days, 1 week, 2 weeks and 8 weeks after injury, four repetitions for each time point) and 4 normal samples. The Bayesian Estimation of Temporal Regulation (BETR) and randomForest packages were used to screen the temporal genes and the top 100 temporal genes, respectively. Then, the gplots package and Pearson correlation analysis separately were used to perform hot map analysis and expression pattern clustering for the top 100 temporal genes. Using the clusterProfiler package and TargetMine tool, their potential functions were analysed by enrichment analyses. Moreover, interaction relationships between these temporal genes and pathways were investigated by pathway-gene crosslinking networks.

RESULTS

In total, 1907 temporal genes were identified. The top 100 temporal genes were obtained and divided into six clusters. Most of the gene functions were enriched in biological process categories. ARG1 and NOS3 in cluster 4 were enriched in biological process of arginine catabolic process. TGFβ2, TGFβ3, ALDH2 and ALDH3A2 were correlated with numerous pathways in the pathway-gene crosslinking network. Pathways related to TGFβ2 and TGFβ3 were connected to pathways related to ARG1 and NOS3 via ARG1.

CONCLUSION

Several temporal genes, including TGFβ2, TGFβ3, ALDH2, ALDH3A2, ARG1 and NOS3, might be involved in SCI.

Long-term anodal block stimulation at sacral anterior roots promoted recovery of neurogenic bladder function in a rabbit model of complete spinal cord injury

A complete spinal cord injury model was established in experimental rabbits using the spinal cord clip compression method. Urodynamic examination was performed 2 weeks later to determine neurogenic bladder status. The rabbits were treated with anodal block stimulation at sacral anterior roots for 4 weeks. Electrical stimulation of sacral anterior roots improved urodynamic parameters of neurogenic bladder in rabbit models of complete spinal cord injury, effectively promoted urinary function, and relieved urinary retention. Immunohistochemistry results showed that a balance was achieved among expression of muscarinic receptor subunits M2, M3, ATP-gated ion channel P2X3 receptors, and β2-adrenergic receptor, and nerve growth factor expression decreased. These results suggested that long-term sacral anterior root stimulation of anodal block could be used to treat neurogenic bladder in a rabbit model of complete spinal cord injury.

S-Nitrosoglutathione protects the spinal bladder: novel therapeutic approach to post-spinal cord injury bladder remodeling

AIMS

Bladder and renal dysfunction are secondary events of the inflammatory processes induced by spinal cord injury (SCI). S-Nitrosoglutathione (GSNO), an endogenous nitrosylating agent is pleiotropic and has anti-inflammatory property. Hence, GSNO ameliorates inflammatory sequelae observed in bladder and renal tissues after SCI. Thus, we postulate that GSNO will improve the recovery of micturition dysfunction by quenching the bladder tissue inflammation associated with SCI.

METHODS

Contusion-based mild SCI was induced in female Sprague-Dawley rats. Sham operated rats served as the controls. SCI rats were gavaged daily with GSNO (50 µg/kg) or vehicle. Bladder function was assessed by urodynamics at 2 and 14 days following SCI. Urine protein concentration and osmolality were measured. Bladder and kidney tissues were analyzed by histology and immunofluorescence for a variety of endpoints related to inflammation.

RESULTS

Two days after SCI, urodynamics demonstrated a hyperreflexive bladder with overflow and no clear micturition events. By Day 14, vehicle animals regained a semblance of a voiding cycle but with no definite intercontraction intervals. GSNO-treated SCI-rats showed nearly normal cystometrograms. Vehicle-treated SCI rats had increased bladder wet weight, proteinuria, and urine osmolality at Day 14, which was reversed by GSNO treatment. In addition, the SCI-induced increase in immune cell infiltration, collagen deposition, iNOS, and ICAM-1 expression and apoptosis were attenuated by GSNO.

CONCLUSIONS

These results indicate that oral administration of GSNO hastens the recovery of bladder function after mild contusion-induced SCI through dampening the inflammation sequelae. These findings also suggest that GSNO-mediated redox modulation may be a novel therapeutic target for the treatment of mild SCI-induced renal and bladder dysfunction.

Arginase promotes skeletal muscle arteriolar endothelial dysfunction in diabetic rats

Endothelial dysfunction is a characteristic feature in diabetes that contributes to the development of vascular disease. Recently, arginase has been implicated in triggering endothelial dysfunction in diabetic patients and animals by competing with endothelial nitric oxide synthase for substrate l-arginine. While most studies have focused on the coronary circulation and large conduit blood vessels, the role of arginase in mediating diabetic endothelial dysfunction in other vascular beds has not been fully investigated. In the present study, we determined whether arginase contributes to endothelial dysfunction in skeletal muscle arterioles of diabetic rats. Diabetes was induced in male Sprague Dawley rats by streptozotocin injection. Four weeks after streptozotocin administration, blood glucose, glycated hemoglobin, and vascular arginase activity were significantly increased. In addition, a significant increase in arginase I and II mRNA expression was detected in gracilis muscle arterioles of diabetic rats compared to age-matched, vehicle control animals. To examine endothelial function, first-order gracilis muscle arterioles were isolated, cannulated in a pressure myograph system, exposed to graded levels of luminal flow, and internal vessel diameter measured. Increases in luminal flow (0–50 μL/min) caused progressive vasodilation in arterioles isolated from control, normoglycemic animals. However, flow-induced vasodilation was absent in arterioles obtained from streptozotocin-treated rats. Acute in vitro pretreatment of blood vessels with the arginase inhibitors N^ω-hydroxy-nor-l-arginine or S-(2-boronoethyl)-l-cysteine restored flow-induced responses in arterioles from diabetic rats and abolished differences between diabetic and control animals. Similarly, acute in vitro pretreatment with l-arginine returned flow-mediated vasodilation in vessels from diabetic animals to that of control rats. In contrast, d-arginine failed to restore flow-induced dilation in arterioles isolated from diabetic animals. Administration of sodium nitroprusside resulted in a similar degree of dilation in arterioles isolated from control or diabetic rats. In conclusion, the present study identifies arginase as an essential mediator of skeletal muscle arteriolar endothelial dysfunction in diabetes. The ability of arginase to induce endothelial dysfunction in skeletal muscle arterioles may further compromise glucose utilization and facilitate the development of hypertension in diabetes.

Common theme for drugs effective in overactive bladder treatment: inhibition of afferent signaling from the bladder

The overactive bladder syndrome and detrusor overactivity are conditions that can have major effects on quality of life and social functioning. Antimuscarinic drugs are still first-line treatment. These drugs often have good initial response rates, but adverse effects and decreasing efficacy cause long-term compliance problems, and alternatives are needed. The recognition of the functional contribution of the urothelium/suburothelium, the autonomous detrusor muscle activity during bladder filling and the diversity of nerve transmitters involved has sparked interest in both peripheral and central modulation of overactive bladder syndrome/detrusor overactivity pathophysiology. Three drugs recently approved for treatment of overactive bladder syndrome/detrusor overactivity (mirabegron, tadalafil and onabotulinum toxin A), representing different pharmacological mechanisms; that is, β-adrenoceptor agonism, phosphodiesterase type 5 inhibition, and inhibition of nerve release of efferent and afferent transmitters, all seem to have one effect in common: inhibition of the afferent nervous activity generated by the bladder during filling. In the present review, the different mechanisms forming the pharmacological basis for the use of these drugs are discussed.

Nitric oxide modulates bladder afferent nerve activity in the in vitro urinary bladder-pelvic nerve preparation from rats with cyclophosphamide induced cystitis

Effects of a nitric oxide (NO) donor (SNAP), NO substrate (l-arginine), and NO synthase inhibitor (l-NAME) on bladder afferent nerve (BAN) activity were studied in an in vitro bladder-pelvic nerve preparation from untreated or cyclophosphamide (CYP) treated rats. Distension of the bladder induced phasic bladder contractions (PBC) that were accompanied by multiunit afferent firing. Intravesical administration of SNAP (2mM) which did not change the amplitude of PBC significantly decreased peak afferent firing from 79 ± 15 spikes/s to 44 ± 8 spikes/s in CYP pretreated but not untreated preparations. In CYP treated preparations SNAP also decreased by 33-55% BAN firing induced by isotonic distension of the bladder at 10-40 cmH(2)O pressures. Electrical stimulation on the surface of the bladder elicited action potentials (AP) in BAN. SNAP significantly increased the voltage threshold by 75% (p<0.05) and decreased by 45% (p<0.05) the area of the AP evoked at submaximal stimulus intensity. Bath application of SNAP (2mM) or l-arginine (50mM) elicited similar inhibitory effects on the distension evoked BAN firing. The effects of l-arginine were blocked by bath application of l-NAME (20mM). l-NAME alone did not alter BAN firing. In preparations from normal rats SNAP or l-arginine did not alter BAN activity. These results suggest that exogenous as well as endogenously generated NO depresses the excitability of sensitized but not normal BAN and that NO may have an antinociceptive function and modulate bladder hyperactivity induced by pathological conditions.

The mechanism of action of phosphodiesterase type 5 inhibitors in the treatment of lower urinary tract symptoms related to benign prostatic hyperplasia

CONTEXT

Clinical trials of phosphodiesterase type 5 inhibitors (PDE5-Is) have consistently demonstrated a significant reduction in lower urinary tract symptoms (LUTS) and small urinary flow rate changes in men with benign prostatic hyperplasia (BPH).

OBJECTIVE

This review presents the proposed mechanisms of action of PDE5-Is in the treatment of BPH-LUTS focusing on the localization of PDE5 isoenzymes in the pelvic structures; smooth muscle relaxation in the bladder, prostate, and supporting vasculature; increased blood perfusion of the bladder and prostate; and modulation of sensory impulses from these organs.

EVIDENCE ACQUISITION

Literature describing in vitro, preclinical, or clinical studies of pathologic processes contributing to LUTS or effects of PDE5 inhibition on the lower urinary tract (LUT) was selected for review.

EVIDENCE SYNTHESIS

We objectively assessed and summarized the published data focusing on articles published within the past 10 yr. Articles before the time cut-off were included if historically relevant.

CONCLUSIONS

The PDE5 isoenzymes are highly expressed in the LUT including the bladder, prostate, and their supporting vasculature. In vitro assays have demonstrated PDE5-Is by regulating cyclic guanosine monophosphate (cGMP) degradation and enhancing the nitric oxide/cGMP signaling pathway to relax human smooth muscle strips from the prostate, bladder, and LUT arteries. In animals characterized by ischemia/hypoxia of the genitourinary tract, treatment with PDE5-Is increases bladder and prostate tissue oxygenation. PDE5-Is have been shown to reduce nonvoiding contractions and bladder afferent nerve firing in decerebrate spinal cord-injured rats, and to reduce mechanosensitive afferent activities of both Aδ- and C-fibers in an irritated or overextended bladder model.

Developmental and spinal cord injury-induced changes in nitric oxide-mediated inhibition in rat urinary bladder

AIMS

During postnatal development large amplitude spontaneous activity of the neonatal rat bladder changes to a low amplitude adult pattern of activity that leads to improved storage function. Previously, we have shown that spontaneous activity in neonatal rat bladder strips is inhibited by activation of the nitric oxide (NO)-cGMP signaling pathway. In the present experiments we determined if this inhibitory pathway is altered during postnatal development or spinal cord injury.

METHODS

Baseline tone and amplitude and frequency of spontaneous contractions were measured in bladder strips from male or female neonatal (days 10-21), juvenile (days 24-39) and adult female spinal cord intact or chronic spinal cord injured Sprague-Dawley rats.

RESULTS

The inhibitory effects of an NO donor (SNAP) and a PDE-5 inhibitor (zaprinast) on spontaneous activity of bladder strips decreased during postnatal development, while an inhibitory effect of 8-bromo-cGMP, which was blocked by a protein kinase G inhibitor, was detected at all ages tested. However, the effect of NO-cGMP signaling to reduce baseline tone emerged during postnatal development. The inhibition induced by the NO donor was blocked by an inhibitor of soluble guanylyl cyclase (sGC). Chronic spinal cord injury (cSCI), which causes the re-emergence of a neonatal-like pattern of spontaneous activity, did not restore sensitivity to NO-mediated inhibition in adult rat bladders.

CONCLUSIONS

These data indicate that while cGMP signaling inhibits activity in young and adult bladders as well as after cSCI, there is a developmental decrease in the sensitivity of bladder to NO-mediated inhibition.

Vardenafil decreases bladder afferent nerve activity in unanesthetized, decerebrate, spinal cord-injured rats

BACKGROUND

Phosphodiesterase type 5 inhibitors (PDE5-Is) improve storage symptoms in benign prostatic hyperplasia patients, despite a lack of effect on peak urinary flow rate. Moreover, vardenafil improves urodynamic parameters in spinal cord-injured (SCI) patients with neurogenic detrusor overactivity (NDO). SCI rats also display NDO characterized by nonvoiding contractions (NVCs) during bladder filling, resulting in an increased bladder afferent nerve firing (BANF).

OBJECTIVE

We postulated that vardenafil could improve urodynamic parameters by reducing BANF. The effect of vardenafil has been investigated on intravesical pressure by cystometry experiments while recording BANF in response to bladder filling.

DESIGN, SETTING, AND PARTICIPANTS

Complete T7-T8 spinalization was performed in 15 female adult Sprague-Dawley rats (250-275 g).

MEASUREMENTS

At 21-29 d postspinalization, fine filaments were dissected from the L6 dorsal roots and placed across a bipolar electrode. Bladder afferent nerve fibers were identified by electrical stimulation of the pelvic nerve and bladder distension. SCI rats were decerebrated before cystometry experiments. Bladders were filled to determine the maximal bladder filling volume (BFV) for each rat. Then, after bladder stabilization at 75% of maximal BFV, saline (n=7) or vardenafil 1 mg/kg (n=8) was delivered intravenously. NVCs and BANF were recorded for 45 min.

RESULTS AND LIMITATIONS

In all SCI rats, BANF was already present and regular at resting conditions (26.2±4.1 spikes per second). During bladder filling, intravesical pressure (IVP) slowly increased with transient NVCs superimposed. Concomitantly, BANF progressively increased up to 2.4-fold at maximal BFV (2.08±0.24 ml). After stabilization at submaximal BFV, BANF was increased by 186±37%. Vardenafil injection induced an immediate decrease in NVCs compared to saline (p<0.001) and BANF (52% decrease vs 28% in saline after 45 min; p<0.001).

CONCLUSIONS

Systemic vardenafil reduced both NVCs and BANF in unanesthetized, decerebrate, SCI rats. These findings provide new insights into the mechanism of action by which PDE5-Is improve storage symptoms in SCI patients.

Pharmacologic therapy for the neurogenic bladder

This article is a review of the current and past literature on medical management of the neurogenic bladder, with a particular focus on spinal cord injury and multiple sclerosis. The use of antimuscarinics, αα-blocker, and tricyclic antidepressants and their combined use are discussed along with new therapies in human and animal trials.

Nitric oxide/cyclic guanosine monophosphate signalling mediates an inhibitory action on sensory pathways of the micturition reflex in the rat

BACKGROUND

Overactive bladder can be associated with a hyperexcitability of bladder afferent C-fibres. Several studies have suggested that nitric oxide (NO) or its downstream signalling could modulate the micturition reflex (MR) by reducing the excitability of bladder afferents.

OBJECTIVES

To evaluate the role of the NO/cyclic guanosine monophosphate (cGMP) signalling pathway on the MR in a model of bladder hyperactivity (BHA) associated with C-fibre activation in the rat.

DESIGN, SETTING, AND PARTICIPANTS

Adult female Sprague Dawley rats were used.

MEASUREMENTS

Cystometry was performed in anaesthetised rats. The effects of 0.1 mg/kg of sodium nitroprusside (SNP), an NO donor; 10 mg/kg of 8Br-cGMP, a cGMP analogue; 3 mg/kg of sildenafil and 1 mg/kg of vardenafil, two phosphodiesterase type 5 inhibitors (PDE5-I); 10 mg/ml of L-N(G)-nitroarginine methyl ester (L-NAME), an NO synthase inhibitor; and 1 mg/kg of LY-83583, a guanylate cyclase inhibitor, were investigated on BHA during intravesical capsaicin (30 micromol/l) instillation. All drugs were delivered intravenously except for L-NAME, which was intravesically administered.

RESULTS AND LIMITATIONS

SNP, 8Br-cGMP, and PDE5-I increased the intercontraction interval (ICI), while SNP and PDE5-I increased the micturition pressure threshold (MPT). L-NAME and LY-83583 decreased MPT, and L-NAME decreased ICI. 8Br-cGMP decreased the maximum intravesical pressure (MP), contrary to L-NAME and LY-83583. SNP and PDE5-I had no effect on MP. SNP increased the voided volume (VV). PDE5-I and 8Br-cGMP also increased VV, although not significantly. In contrast, L-NAME tended to decrease VV. Although 8Br-cGMP decreased the baseline intravesical pressure, LY-83583 increased it. Neither SNP nor PDE5-I nor L-NAME had any effect on baseline pressure.

CONCLUSIONS

Compounds activating the NO/cGMP pathway inhibited BHA, whereas compounds inhibiting the NO/cGMP pathway increased it. These results indicate that the NO/cGMP signalling pathway is involved in the regulation of the MR, with an action that seems more predominant on the sensory rather on the motor component of the MR in a rat model of BHA associated with C-fibre afferent activation.

Simvastatin protects bladder and renal functions following spinal cord injury in rats

BACKGROUND

Urinary bladder and renal dysfunction are secondary events associated with spinal cord injury (SCI) in humans. These secondary events not only compromise quality of life but also delay overall recovery from SCI pathophysiology. Furthermore, in experimental models the effects of SCI therapy on bladder and renal functions are generally not evaluated. In this study, we tested whether simvastatin improves bladder and renal functions in a rat model of experimental SCI.

METHODS

SCI was induced by controlled contusion of T9-T10 in adult female rats. Simvastatin (5 mg/Kg body weight) was administered at two hours after SCI and repeated every 24 hours until the end point. Simvastatin-treated SCI animals (simvastatin group) were compared with vehicle-treated SCI animals (vehicle group) in terms of the Basso Beattie Bresnahan score, tissue morphology, cell death, and bladder/renal functions.

RESULTS

The urinary bladder of vehicle animals showed a 4.3-fold increase in size and a 9-fold increase in wet weight compared to sham animals. Following SCI, the urine to plasma osmolality ratio increased initially but decreased 1 week after SCI. Hematoxylin and eosin staining of bladder tissue showed transitional epithelial hyperplasia, degeneration of lamina propria, and enlargement of tunica adventia in addition to detrusor muscle hypertrophy. Rats treated with simvastatin for 14 days displayed remarkable recovery by showing decreased bladder size and maintenance of a normal urine/plasma osmolality ratio, in addition to improved locomotion. The muscularis layer of the bladder also regained its compact nature in simvastatin animals. Moreover, SCI-induced renal caspase-3 activity was significantly decreased in the simvastatin group indicating the ability of simvastatin to reduce the renal tubular apoptosis.

CONCLUSION

Post-injury administration of simvastatin ameliorates bladder and renal dysfunction associated with SCI in rats.

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.