Roles of adenosine A1 and A2A receptors in the control of micturition in rats

Activation of the adenosine A1 receptor in the lumbosacral spinal cord improves bladder overactivity in rats with cystitis induced by cyclophosphamide

PURPOSE

To investigate the effect of intrathecal administration of CCPA, an adenosine A1 receptor agonist, on voiding function in rats with cystitis induced by cyclophosphamide (CYP).

METHODS

Thirty 8-week-old Sprague Dawley rats were randomly divided into a control group (n = 15) and a cystitis group (n = 15). Cystitis was induced by a single intraperitoneal injection of CYP (200 mg/kg, dissolved in physiological saline) in rats. Control rats were injected intraperitoneally with physiological saline. The PE10 catheter reached the level of L6-S1 spinal cord through L3-4 intervertebral space for intrathecal injection. Forty-eight hours after intraperitoneal injection, urodynamic tests were conducted to observe the effect of intrathecal administration of 10% dimethylsulfoxide (vehicle) and 1 nmol CCPA on micturition parameters, including basal pressure (BP), threshold pressure (TP), maximal voiding pressure (MVP), intercontraction interval (ICI), voided volume (VV), residual volume (RV), bladder capacity (BC), and voiding efficiency (VE). Histological changes of the bladder of cystitis rats were studied through hematoxylin-eosin staining (HE staining). Moreover, Western blot and immunofluorescence were used to study the expression of adenosine A1 receptor in the L6-S1 dorsal spinal cord in both groups of rats.

RESULTS

HE staining revealed submucosal hemorrhage, edema, and inflammatory cell infiltration in the bladder wall of cystitis rats. The urodynamic test showed significant increase in BP, TP, MVP and RV in cystitis rats, while ICI, VV, BC and VE decreased significantly, indicating bladder overactivity. CCPA inhibited the micturition reflex in both control and cystitis rats, and significantly increased TP, ICI, VV, BC, and VE, but had no significant effect on BP, MVP and RV. Western blot and immunofluorescence showed that there was no significant difference in the expression of adenosine A1 receptor in the L6-S1 dorsal spinal cord between the control and cystitis rats.

CONCLUSION

The findings of this study suggest that intrathecal administration of the adenosine A1 receptor agonist CCPA alleviates CYP-induced bladder overactivity. Furthermore, our results indicate that the adenosine A1 receptor in the lumbosacral spinal cord may be a promising target for treatment of bladder overactivity.

Sensory Neurons, PIEZO Channels and PAC1 Receptors Regulate the Mechanosensitive Release of Soluble Ectonucleotidases in the Murine Urinary Bladder Lamina Propria

The urinary bladder requires adequate concentrations of extracellular adenosine 5'-triphosphate (ATP) and other purines at receptor sites to function properly. Sequential dephosphorylation of ATP to ADP, AMP and adenosine (ADO) by membrane-bound and soluble ectonucleotidases (s-ENTDs) is essential for achieving suitable extracellular levels of purine mediators. S-ENTDs, in particular, are released in the bladder suburothelium/lamina propria (LP) in a mechanosensitive manner. Using 1,N⁶-etheno-ATP (eATP) as substrate and sensitive HPLC-FLD methodology, we evaluated the degradation of eATP to eADP, eAMP and eADO in solutions that were in contact with the LP of ex vivo mouse detrusor-free bladders during filling prior to substrate addition. The inhibition of neural activity with tetrodotoxin and ω-conotoxin GVIA, of PIEZO channels with GsMTx4 and D-GsMTx4 and of the pituitary adenylate cyclase-activating polypeptide type I receptor (PAC1) with PACAP6-38 all increased the distention-induced but not spontaneous release of s-ENTDs in LP. It is conceivable, therefore, that the activation of these mechanisms in response to distention restricts the further release of s-ENTDs and prevents excessive hydrolysis of ATP. Together, these data suggest that afferent neurons, PIEZO channels, PAC1 receptors and s-ENTDs form a system that operates a highly regulated homeostatic mechanism to maintain proper extracellular purine concentrations in the LP and ensure normal bladder excitability during bladder filling.

Initiating daily acute intermittent hypoxia (dAIH) therapy at 1-week after contusion spinal cord injury (SCI) improves lower urinary tract function in rat

Spinal cord injury (SCI) above the level of the lumbosacral spinal cord produces lower urinary tract (LUT) dysfunction, resulting in impairment of urine storage and elimination (voiding). While spontaneous functional recovery occurs due to remodeling of spinal reflex micturition pathways, it is incomplete, indicating that additional strategies to further augment neural plasticity following SCI are essential. To this end, acute intermittent hypoxia (AIH) exposure has been proposed as a therapeutic strategy for improving recovery of respiratory and other somatic motor function following SCI; however, the impact of AIH as a therapeutic intervention to improve LUT dysfunction remains to be determined. Therefore, we examined the effects of daily AIH (dAIH) on both spontaneous micturition patterns and reflex micturition event (rME) behaviors in adult female Sprague-Dawley rats with mid-thoracic moderate contusion SCI. For these experiments, dAIH gas exposures (five alternating 3 min 12% O₂ and 21% O₂ episodes) were delivered for 7 consecutive days beginning at 1-week after SCI, with awake micturition patterns being evaluated weekly for 2-3 sessions before and for 4 weeks after SCI and rME behaviors elicited by continuous infusion of saline into the bladder being evaluated under urethane anesthesia at 4-weeks after SCI; daily normoxia (dNx; 21% O₂ episodes) served as a control. At 1-week post-SCI, both an areflexic phenotype (i.e., no effective voiding events) and a functional voiding phenotype (i.e., infrequent voiding events with large volumes) were observed in spontaneous micturition patterns (as expected), and subsequent dAIH, but not dNx, treatment led to recovery of spontaneous void frequency pattern to pre-SCI levels; both dAIH- and dNx-treated rats exhibited slightly increased void volumes. At 4-weeks post-SCI, rME behaviors showed increased effectiveness in voiding in dAIH-treated (compared to dNx-treated) rats that included an increase in both bladder contraction pressure (delta BP; P = 0.014) and dynamic voiding efficiency (P = 0.018). Based on the voiding and non-voiding bladder contraction behaviors (VC and NVC, respectively) observed in the BP records, bladder dysfunction severity was classified into mild, moderate, and severe phenotypes, and while rats in both treatment groups included each severity phenotype, the primary phenotype observed in dAIH-treated rats was mild and that in dNx-treated rats was moderate (P = 0.044). Taken together, these findings suggest that 7-day dAIH treatment produces beneficial improvements in LUT function that include recovery of micturition pattern, more efficient voiding, and decreased NVCs, and extend support to the use of dAIH therapy to treat SCI-induced LUT dysfunction.

Urinary ATP Levels Are Controlled by Nucleotidases Released from the Urothelium in a Regulated Manner

Adenosine 5′-triphosphate (ATP) is released in the bladder lumen during filling. Urothelial ATP is presumed to regulate bladder excitability. Urinary ATP is suggested as a urinary biomarker of bladder dysfunctions since ATP is increased in the urine of patients with overactive bladder, interstitial cystitis or bladder pain syndrome. Altered urinary ATP might also be associated with voiding dysfunctions linked to disease states associated with metabolic syndrome. Extracellular ATP levels are determined by ATP release and ATP hydrolysis by membrane-bound and soluble nucleotidases (s-NTDs). It is currently unknown whether s-NTDs regulate urinary ATP. Using etheno-ATP substrate and HPLC-FLD detection techniques, we found that s-NTDs are released in the lumen of ex vivo mouse detrusor-free bladders. Capillary immunoelectrophoresis by ProteinSimple Wes determined that intraluminal solutions (ILS) collected at the end of filling contain ENTPD3 > ENPP1 > ENPP3 ≥ ENTPD2 = NT5E = ALPL/TNAP. Activation of adenylyl cyclase with forskolin increased luminal s-NTDs release whereas the AC inhibitor SQ22536 had no effect. In contrast, forskolin reduced and SQ22536 increased s-NTDs release in the lamina propria. Adenosine enhanced s-NTDs release and accelerated ATP hydrolysis in ILS and lamina propria. Therefore, there is a regulated release of s-NTDs in the bladder lumen during filling. Aberrant release or functions of urothelial s-NTDs might cause elevated urinary ATP in conditions with abnormal bladder excitability.

Mechanosensitive Hydrolysis of ATP and ADP in Lamina Propria of the Murine Bladder by Membrane-Bound and Soluble Nucleotidases

Prior studies suggest that urothelium-released adenosine 5′-triphosphate (ATP) has a prominent role in bladder mechanotransduction. Urothelial ATP regulates the micturition cycle through activation of purinergic receptors that are expressed in many cell types in the lamina propria (LP), including afferent neurons, and might also be important for direct mechanosensitive signaling between urothelium and detrusor. The excitatory action of ATP is terminated by enzymatic hydrolysis, which subsequently produces bioactive metabolites. We examined possible mechanosensitive mechanisms of ATP hydrolysis in the LP by determining the degradation of 1,N⁶-etheno-ATP (eATP) at the anti-luminal side of nondistended (empty) or distended (full) murine (C57BL/6J) detrusor-free bladder model, using HPLC. The hydrolysis of eATP and eADP was greater in contact with LP of distended than of nondistended bladders whereas the hydrolysis of eAMP remained unchanged during filling, suggesting that some steps of eATP hydrolysis in the LP are mechanosensitive. eATP and eADP were also catabolized in extraluminal solutions (ELS) that were in contact with the LP of detrusor-free bladders, but removed from the organ chambers prior to addition of substrate. The degradation of both purines was greater in ELS from distended than from nondistended preparations, suggesting the presence of mechanosensitive release of soluble nucleotidases in the LP. The released enzyme activities were affected differently by Ca²⁺ and Mg²⁺. The common nucleotidase inhibitors ARL67156, POM-1, PSB06126, and ENPP1 Inhibitor C, but not the alkaline phosphatase inhibitor (-)-p-bromotetramisole oxalate, inhibited the enzymes released during bladder distention. Membrane-bound nucleotidases were identified in tissue homogenates and in concentrated ELS from distended preparations by Wes immunodetection. The relative distribution of nucleotidases was ENTPD1 >> ENPP1 > ENTPD2 = ENTPD3 > ENPP3 = NT5E >> ENTPD8 = TNAP in urothelium and ENTPD1 >> ENTPD3 >> ENPP3 > ENPP1 = ENTPD2 = NT5E >> ENTPD8 = TNAP in concentrated ELS, suggesting that regulated ectodomain shedding of membrane-bound nucleotidases possibly occurs in the LP during bladder filling. Mechanosensitive degradation of ATP and ADP by membrane-bound and soluble nucleotidases in the LP diminishes the availability of excitatory purines in the LP at the end of bladder filling. This might be a safeguard mechanism to prevent over-excitability of the bladder. Proper proportions of excitatory and inhibitory purines in the bladder wall are determined by distention-associated purine release and purine metabolism.

Suppression of adenosine A2a receptors alleviates bladder overactivity and hyperalgesia in cyclophosphamide-induced cystitis by inhibiting TRPV1

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a type of chronic bladder inflammation characterized by increased voiding frequency, urgency and pelvic pain. The sensitization of bladder afferents is widely regarded as one of the pathophysiological changes in the development of IC/BPS. There is evidence that adenosine A_2a receptors are involved in regulating the sensitization of sensory afferents. However, the effect of adenosine A_2a receptors on cystitis remains unknown. In the present study, a rat model of chronic cystitis was established by intraperitoneal injection with cyclophosphamide (CYP). Cystometry and behavioral tests were performed to investigate bladder micturition function and nociceptive pain. The rats with chronic cystitis showed symptoms of bladder overactivity, characterized by an increase in bladder voiding frequency and voiding pressure. CYP treatment significantly increased the expression of the A_2a receptor in bladder afferent fibers and dorsal root ganglion (DRG) neurons. The A_2a receptor antagonist ZM241385 prevented bladder overactivity and hyperalgesia elicited by CYP-induced cystitis. In addition, the A_2a receptor and TRPV1 were coexpressed on DRG neurons. The TRPV1 antagonist capsazepine blocked bladder overactivity induced by the A_2a receptor agonist CGS21680. In contrast, ZM241385 significantly inhibited the capsaicin-induced increase in intracellular calcium concentration in DRG neurons. These results suggest that suppression of adenosine A_2a receptors in bladder afferents alleviates bladder overactivity and hyperalgesia elicited by CYP-induced cystitis in rats by inhibiting TRPV1, indicating that the adenosine A_2a receptor in bladder afferents is a potential therapeutic target for the treatment of IC/BPS.

The Urothelium: Life in a Liquid Environment

The urothelium, which lines the renal pelvis, ureters, urinary bladder, and proximal urethra, forms a high-resistance but adaptable barrier that surveils its mechanochemical environment and communicates changes to underlying tissues including afferent nerve fibers and the smooth muscle. The goal of this review is to summarize new insights into urothelial biology and function that have occurred in the past decade. After familiarizing the reader with key aspects of urothelial histology, we describe new insights into urothelial development and regeneration. This is followed by an extended discussion of urothelial barrier function, including information about the roles of the glycocalyx, ion and water transport, tight junctions, and the cellular and tissue shape changes and other adaptations that accompany expansion and contraction of the lower urinary tract. We also explore evidence that the urothelium can alter the water and solute composition of urine during normal physiology and in response to overdistension. We complete the review by providing an overview of our current knowledge about the urothelial environment, discussing the sensor and transducer functions of the urothelium, exploring the role of circadian rhythms in urothelial gene expression, and describing novel research tools that are likely to further advance our understanding of urothelial biology.

Which molecular targets do we need to focus on to improve lower urinary tract dysfunction? ICI-RS 2017

AIMS

Update on some molecular targets for new drugs to improve lower urinary tract (LUT) dysfunction.

METHODS

Using PubMed, a search for literature on molecular targets in the LUT was performed to identify relevant clinical and animal studies. Keywords were entered as Medical Subject Headings (MeSH) or as text words. The Mesh terms were used in various combinations and usually included the terms lower urinary AND pharmacology. Other Mesh term included: bladder, urethra, CNS, physiology, afferent activity, ATP, prostanoids, cannabinoids, fibrosis. Search results were assessed for their overall relevance to this review.

RESULTS

In a normal bladder, ATP contributes little to detrusor contraction, but in a diseased bladder ATP may contribute to OAB. Selective decrease of ATP release via adenosine A1 receptor stimulation offers a potential treatment possibility. Candidates for relaxation of the smooth muscle of the urethra can be found among, for example, the receptor subtypes of PGE₂ , and PGD₂ . Drugs for relaxation of the striated sphincter can target the muscle directly or the spinal sphincter control. Fibrosis is a major problem in LUT dysfunction and agents with an inhibitory effect on the TGFβ pathway, for example relaxin and BMP7, may be promising avenues. Available drugs with a CNS site of action are often limited by low efficacy or adverse effects. Inhibitors of the glycine receptor Gly-T2 or antagonists of the adenosine A2 receptor may be new alternatives.

CONCLUSION

New molecular targets for drugs aiming at improvement of voiding function can be identified, but their translational impact remains to be established.

Purinergic P2X7 receptors as therapeutic targets in interstitial cystitis/bladder pain syndrome; key role of ATP signaling in inflammation

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic lower urinary tract condition. Patients with IC/BPS suffer from debilitating pain and urinary urgency. The underlying etiology of IC/BPS is unknown and as such current treatments are mostly symptomatic with no real cure. Many theories have been proposed to describe the etiology of IC/BPS, but this review focuses on the role of inflammation. In IC/BPS patients, the permeability of the urothelium barrier is compromised and inflammatory cells infiltrate the bladder wall. There are increased levels of many inflammatory mediators in patients with IC/BPS and symptoms such as pain and urgency that have been associated with the degree of inflammation. Recent evidence has highlighted the role of purinergic receptors, specifically the P2X7 receptor, in the process of inflammation. The results from studies in animals including cyclophosphamide-induced hemorrhagic cystitis strongly support the role of P2X7 receptors in inflammation. Furthermore, the deletion of the P2X7 receptor or antagonism of this receptor significantly reduces inflammatory mediator release from the bladder and improves symptoms. Research results from IC/BPS patients and animal models of IC/BPS strongly support the crucial role of inflammation in the pathophysiology of this painful disease. Purinergic signaling and purinergic receptors, especially the P2X7 receptor, play an undisputed role in inflammation. Purinergic receptor antagonists show positive results in treating different symptoms of IC/BPS.

Inosine - a Multifunctional Treatment for Complications of Neurologic Injury

Spinal cord injury (SCI) caused by trauma or disease leads to motor and sensory abnormalities that depend on the level, severity and duration of the lesion. The most obvious consequence of SCI is paralysis affecting lower and upper limbs. SCI also leads to loss of bladder and bowel control, both of which have a deleterious, life-long impact on the social, psychological, functional, medical and economic well being of affected individuals. Currently, there is neither a cure for SCI nor is there adequate management of its consequences. Although medications provide symptomatic relief for the complications of SCI including muscle spasms, lower urinary tract dysfunction and hyperreflexic bowel, strategies for repair of spinal injuries and recovery of normal limb and organ function are still to be realized. In this review, we discuss experimental evidence supporting the use of the naturally occurring purine nucleoside inosine to improve the devastating sequelae of SCI. Evidence suggests inosine is a safe, novel agent with multifunctional properties that is effective in treating complications of SCI and other neuropathies.

Long-term Outcome of Adenosine A2A Receptor Antagonist on Lower Urinary Tract Symptoms in Male Parkinson Disease Patients

Supplemental digital content is available in the text.

Objectives

In addition to motor symptoms, bladder dysfunction is a major clinical issue in patients with Parkinson disease (PD). Istradefylline is adenosine A2A receptor antagonist approved for PD patients with wearing-off symptoms. The aim of this study was to determine the long-term effects of istradefylline on lower urinary tract symptoms (LUTSs) in PD patients.

Methods

We enrolled 14 male PD patients. The mean age of patients was 73 years (61–77 years), the Hoehn-Yahr stage was 2 (2–3), and disease duration was 9 years (3–28 years). The effects of istradefylline (20 mg/d) on LUTSs in PD patients with motor complications after 3, 6, and 12 months of therapy were evaluated based on the International Prostate Symptom Score and Overactive Bladder Symptom Score before and after its administration.

Results

Motor symptoms significantly improved at 12 months' administration (Movement Disorder Society–sponsored revision of the Unified Parkinson's Disease Rating Scale part III: 30.0 ± 12.9 vs 13.8 ± 8.1; P < 0.01). Significant improvements were also observed in the answers provided on urinary questionnaires (International Prostate Symptom Score, 14.4 ± 7.6 vs 8.5 ± 6.8; Overactive Bladder Symptom Score, 6.9 ± 2.8 vs 5.5 ± 3.7; P < 0.05). Nighttime urinary frequency and the percentage of the nocturnal urine volume also improved significantly at 3 months' administration (P < 0.01).

Conclusions

Istradefylline effectively improved not only motor symptoms, but also LUTSs in patients with PD.

Istradefylline improves daytime sleepiness in patients with Parkinson's disease: An open-label, 3-month study

BACKGROUND

Istradefylline, a selective adenosine A2A receptor antagonist, has been reported to improve daily "off time" and motor symptoms in patients with Parkinson's disease (PD). However, the effect of istradefylline on sleep problems has not been thoroughly investigated.

METHODS

We evaluated the effect of istradefylline on daytime sleepiness, sleep disturbances, and motor symptoms in 22 PD patients who were affected by the wearing off phenomenon in an open-label, 3-month study. Participants received 20-40mg/day istradefylline once daily (morning) over a 3-month period. The Epworth Sleepiness Scale (ESS), PD sleep scale (PDSS)-2 and PD Questionnaire (PDQ-8) were administered at baseline, 2weeks, 1month, 2months and 3months. At baseline and 3months, patients were evaluated on the Movement Disorder Society Revision of the Unified PD Rating Scale (MDS-UPDRS) parts III and IV.

RESULTS

Twenty-one patients (95.5%) completed the study. At 3months, MDS-UPDRS part III (-5.3, p=0.0002) and part IV (-2.5, p=0.001) scores improved and off time decreased significantly (-50.1min, p=0.0004). PDQ-8 scores were unchanged at 3months. ESS scores decreased significantly at 2months and 3months (-2.4 and -3.3, respectively, p<0.0001), but the total PDSS-2 scores did not change.

CONCLUSION

Istradefylline improved daytime sleepiness in PD patients, possibly through its effect on enhancing alertness. In addition, the lack of significant changes in the total PDSS-2 scores over the study period suggests istradefylline had no negative impact on sleep.

Inhibition of cholinergic neurotransmission by β3-adrenoceptors depends on adenosine release and A1-receptor activation in human and rat urinary bladders

The direct detrusor relaxant effect of β₃-adrenoceptor agonists as a primary mechanism to improve overactive bladder symptoms has been questioned. Among other targets, activation of β₃-adrenoceptors downmodulate nerve-evoked acetylcholine (ACh) release, but there is insufficient evidence for the presence of these receptors on bladder cholinergic nerve terminals. Our hypothesis is that adenosine formed from the catabolism of cyclic AMP in the detrusor may act as a retrograde messenger via prejunctional A₁ receptors to explain inhibition of cholinergic activity by β₃-adrenoceptors. Isoprenaline (1 µM) decreased [³H]ACh release from stimulated (10 Hz, 200 pulses) human (-47 ± 5%) and rat (-38 ± 1%) detrusor strips. Mirabegron (0.1 µM, -53 ± 8%) and CL316,243 (1 µM, -37 ± 7%) mimicked isoprenaline (1 µM) inhibition, and their effects were prevented by blocking β₃-adrenoceptors with L748,337 (30 nM) and SR59230A (100 nM), respectively, in human and rat detrusor. Mirabegron and isoprenaline increased extracellular adenosine in the detrusor. Blockage of A₁ receptors with 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 100 nM) or the equilibrative nucleoside transporters (ENT) with dipyridamole (0.5 µM) prevented mirabegron and isoprenaline inhibitory effects. Dipyridamole prevented isoprenaline-induced adenosine outflow from the rat detrusor, and this effect was mimicked by the ENT1 inhibitor, S-(4-nitrobenzyl)-6-thioinosine (NBTI, 30 µM). Cystometry recordings in anesthetized rats demonstrated that SR59230A, DPCPX, dipyridamole, and NBTI reversed the decrease in the voiding frequency caused by isoprenaline (0.1-1,000 nM). Data suggest that inhibition of cholinergic neurotransmission by β₃-adrenoceptors results from adenosine release via equilibrative nucleoside transporters and prejunctional A₁-receptor stimulation in human and rat urinary bladder.

Inosine attenuates spontaneous activity in the rat neurogenic bladder through an A2B pathway

Neurogenic detrusor overactivity (NDO) is among the most challenging complications of spinal cord injury (SCI). A recent report by us demonstrated an improvement in NDO in SCI rats following chronic systemic treatment with the purine nucleoside inosine. The objective of this study was to investigate the mechanism of action of inosine underlying improvement of NDO. Male Sprague-Dawley rats underwent complete spinal cord transection at T8. Inosine (1 mM) delivered intravesically to SCI rats during conscious cystometry significantly decreased the frequency of spontaneous non-voiding contractions. In isolated tissue assays, inosine (1 mM) significantly decreased the amplitude of spontaneous activity (SA) in SCI bladder muscle strips. This effect was prevented by a pan-adenosine receptor antagonist CGS15943, but not by A₁ or A₃ receptor antagonists. The A_2A antagonist ZM241385 and A_2B antagonist PSB603 prevented the effect of inosine. The effect of inosine was mimicked by the adenosine receptor agonist NECA and the A_2B receptor agonist BAY60-6583. The inhibition of SA by inosine was not observed in the presence of the BK antagonist, iberiotoxin, but persisted in the presence of K_ATP and SK antagonists. These findings demonstrate that inosine acts via an A_2B receptor-mediated pathway that impinges on specific potassium channel effectors.

Contractile effects and receptor analysis of adenosine-receptors in human detrusor muscle from stable and neuropathic bladders

To measure the relative transcription of adenosine receptor subtypes and the contractile effects of adenosine and selective receptor-subtype ligands on detrusor smooth muscle from patients with neuropathic overactive (NDO) and stable bladders and also from guinea-pigs. Contractile function was measured at 37°C in vitro from detrusor smooth muscle strips. Contractions were elicited by superfusate agonists or by electrical field stimulation. Adenosine-receptor (A1, A2A, A2B, A3) transcription was measured by RT-PCR. Adenosine attenuated nerve-mediated responses with equivalent efficacy in human and guinea-pig tissue (pIC50 3.65–3.86); the action was more effective at low (1–8 Hz) compared to high (20–40 Hz) stimulation frequencies in human NDO and guinea-pig tissue. With guinea-pig detrusor the action of adenosine was mirrored by the A1/A2-agonist N-ethylcarboxamidoadenosine (NECA), partly abolished in turn by the A2B-selectve antagonist alloxazine, as well as the A1-selective agonist N6- cyclopentyladenosine (CPA). With detrusor from stable human bladders the effects of NECA and CPA were much smaller than that of adenosine. Adenosine also attenuated carbachol contractures, but mirrored by NECA (in turn blocked by alloxazine) only in guinea-pig tissue. Adenosine receptor subtype transcription was measured in human detrusor and was similar in both groups, except reduced A2A levels in overactive bladder. Suppression of the carbachol contracture in human detrusor is independent of A-receptor activation, in contrast to an A2B-dependent action with guinea-pig tissue. Adenosine also reduced nerve-mediated contractions, by an A1- dependent action suppressing ATP neurotransmitter action.

A1 Adenosine Receptor-Mediated Inhibition of Parasympathetic Neuromuscular Transmission in Human and Murine Urinary Bladder

The potential role of A1 adenosine receptors in modulating neuromuscular transmission in the detrusor muscle of the urinary bladder has been tested in human and murine preparations with the intent to determine the viability of using adenosine receptor agonists as adjuncts to treat overactive bladder. In human detrusor muscle preparations, contractile responses to electrical field stimulation were inhibited by the selective A1 adenosine receptor agonists 2-chloro-N(6)-cyclopentyladenosine, N(6)-cyclopentyladenosine (CPA), and adenosine (rank order of potency: 2-chloro-N(6)-cyclopentyladenosine > CPA > adenosine). Pretreatment with 8-cyclopentyl-3-[3-[[4(fluorosulphonyl)benzoyl]oxy]propyl]-1-propylxanthine, an irreversible A1 antagonist, blocked the effects of CPA, thus confirming the role of A1 receptors in human detrusor preparations. In murine detrusor muscle preparations, contractions evoked by electrical field stimulation were reduced by CPA or adenosine. Amplitudes of the P2X purinoceptor-mediated excitatory junctional potentials (EJPs) recorded with intracellular microelectrodes were reduced in amplitude by CPA and adenosine with no effect on the spontaneous EJP amplitudes, confirming the prejunctional action of these agents. 8-Cyclopentyltheophylline, a selective A1 receptor antagonist, reversed the effects of CPA on EJP amplitudes with no effect of spontaneous EJPs, confirming the role of A1 receptors in mediating these effects.

Impairment of ATP hydrolysis decreases adenosine A1 receptor tonus favoring cholinergic nerve hyperactivity in the obstructed human urinary bladder

This study was designed to investigate whether reduced adenosine formation linked to deficits in extracellular ATP hydrolysis by NTPDases contributes to detrusor neuromodulatory changes associated with bladder outlet obstruction in men with benign prostatic hyperplasia (BPH). The kinetics of ATP catabolism and adenosine formation as well as the role of P1 receptor agonists on muscle tension and nerve-evoked [(3)H]ACh release were evaluated in mucosal-denuded detrusor strips from BPH patients (n = 31) and control organ donors (n = 23). The neurogenic release of ATP and [(3)H]ACh was higher (P < 0.05) in detrusor strips from BPH patients. The extracellular hydrolysis of ATP and, subsequent, adenosine formation was slower (t (1/2) 73 vs. 36 min, P < 0.05) in BPH detrusor strips. The A(1) receptor-mediated inhibition of evoked [(3)H]ACh release by adenosine (100 μM), NECA (1 μM), and R-PIA (0.3 μM) was enhanced in BPH bladders. Relaxation of detrusor contractions induced by acetylcholine required 30-fold higher concentrations of adenosine. Despite VAChT-positive cholinergic nerves exhibiting higher A(1) immunoreactivity in BPH bladders, the endogenous adenosine tonus revealed by adenosine deaminase is missing. Restoration of A1 inhibition was achieved by favoring (1) ATP hydrolysis with apyrase (2 U mL(-1)) or (2) extracellular adenosine accumulation with dipyridamole or EHNA, as these drugs inhibit adenosine uptake and deamination, respectively. In conclusion, reduced ATP hydrolysis leads to deficient adenosine formation and A(1) receptor-mediated inhibition of cholinergic nerve activity in the obstructed human bladder. Thus, we propose that pharmacological manipulation of endogenous adenosine levels and/or A(1) receptor activation might be useful to control bladder overactivity in BPH patients.

Signalling molecules in the urothelium

The urothelium was long considered to be a silent barrier protecting the body from the toxic effects of urine. However, today a number of dynamic abilities of the urothelium are well recognized, including its ability to act as a sensor of the intravesical environment. During recent years several pathways of these urothelial abilities have been proposed and a major part of these pathways includes release of signalling molecules. It is now evident that the urothelium represents only one part of the sensory web. Urinary bladder signalling is finely tuned machinery of signalling molecules, acting in autocrine and paracrine manner, and their receptors are specifically distributed among different types of cells in the urinary bladder. In the present review the current knowledge of the formation, release, and signalling effects of urothelial acetylcholine, ATP, adenosine, and nitric oxide in health and disease is discussed.