Endogenous purinergic control of bladder activity via presynaptic P2X3 and P2X2/3 receptors in the spinal cord.

P2X(3) and P2X(2/3) receptors are localized on sensory afferents both peripherally and centrally and have been implicated in various sensory functions. However, the physiological role of these receptors expressed presynaptically in the spinal cord in regulating sensory transmission remains to be elucidated. Here, a novel selective P2X(3) and P2X(2/3) antagonist, AF-792 [5-(5-ethynyl-2-isopropyl-4-methoxy-phenoxy)-pyrimidine-2,4-diamine, previously known as RO-5], in addition to less selective purinoceptor ligands, was applied intrathecally in vivo. Cystometry recordings were made to assess changes in the micturition reflex contractions after drug treatments. We found that AF-792 inhibited micturition reflex activity significantly (300 nmol; from baseline contraction intervals of 1.18 +/- 0.07 to 9.33 +/- 2.50 min). Furthermore, inhibition of P2X(3) and P2X(2/3) receptors in the spinal cord significantly attenuated spinal activation of extracellular-signal regulated kinases induced by acute peripheral stimulation of the bladder with 1% acetic acid by 46.4 +/- 12.0% on average. Hence, the data suggest that afferent signals originating from the bladder are regulated by spinal P2X(3) and P2X(2/3) receptors and establish directly an endogenous central presynaptic purinergic mechanism to regulate visceral sensory transmission. Identification of this spinal purinergic control in visceral activities may help the development of P2X(3) and P2X(2/3) antagonist to treat urological dysfunction, such as overactive bladder, and possibly other debilitating sensory disorders, including chronic pain states.

Selective pharmacological blockade of the TRPV1 receptor suppresses sensory reflexes of the rodent bladder.

PURPOSE: We investigated the pharmacological effect of TRPV1 antagonists in anesthetized rodent models of bladder function. MATERIALS AND METHODS: The TRPV1 antagonists JNJ17203212 and JYL1421 were evaluated in the anesthetized rat volume induced micturition reflex model. JNJ17203212 was further evaluated in this model in capsaicin (Sigma) desensitized rats, and in rat capsaicin and mouse citric acid models of irritant induced detrusor overactivity. RESULTS: Systemic JNJ17203212 and JYL1421 administration in the anesthetized rat volume induced micturition reflex model resulted in an increased micturition threshold volume. JNJ17203212 also decreased bladder contraction amplitude but JYL1421 had no effect. Capsaicin desensitization significantly increased baseline micturition threshold volume and decreased bladder contraction amplitude in the volume induced micturition reflex model compared to those in sham treated controls and JNJ17203212 produced no further effect after capsaicin desensitization. JNJ17203212 was also effective in 2 models of irritant induced detrusor overactivity, preventing the decrease in micturition threshold volume and the increase in bladder contraction amplitude observed with intravesical instillation of 10 microM capsaicin, and the decreased voiding interval induced by intravesical citric acid. CONCLUSIONS: The TRPV1 antagonists JNJ17203212 and JYL1421 increased the threshold for activation of the micturition reflex in the anesthetized rat volume induced micturition reflex model. This effect appeared to be mediated by capsaicin sensitive afferents. JNJ17203212 also inhibited detrusor overactivity induced by intravesical capsaicin and intravesical citric acid. These data extend our understanding of the role of TRPV1 in sensory modulation of the micturition reflex under nonirritant and inflammatory conditions.

Effects of the selective prostacyclin receptor antagonist RO3244019 on the micturition reflex in rats.

PURPOSE: We investigated the role of prostacyclin on afferent modulation of the micturition reflex using the novel selective prostacyclin receptor antagonist RO3244019 in rat models of bladder function. MATERIALS AND METHODS: The effects of RO3244019 on urodynamic parameters were evaluated in 3 rat models. In the anesthetized isovolumetric bladder contraction and the volume induced micturition reflex (Refill) models the effects of RO3244019 and chronic capsaicin desensitization were compared. In the citric acid induced detrusor overactivity model the effects of RO3244019 and the cyclooxygenase inhibitor indomethacin were evaluated. RESULTS: In the isovolumetric bladder contraction model RO3244019 dose dependently decreased bladder contraction frequency with a mean +/- SEM maximum decrease of 72.2% +/- 4.3% at 3.16 mg/kg. RO3244019 also dose dependently increased the micturition threshold in the Refill model with a maximum increase of 86.9% +/- 19.1% at 3.0 mg/kg. In animals that were chronically treated with capsaicin bladder contraction frequency was decreased by 88.9% in the isovolumetric bladder contraction model and micturition threshold was increased by 68.1% in the Refill model relative to sham treated rats. RO3244019 (3.0 mg/kg) further increased the micturition threshold in capsaicin treated animals by 53.7% +/- 18.1% from baseline. In the citric acid induced detrusor overactivity model citric acid decreased the voiding interval to 28.5% of baseline. This effect was reversed by RO3244019 (73.0% +/- 6.4%) and indomethacin (97.7% +/- 5.5%) at 3.0 mg/kg compared to vehicle (55.0% +/- 4.1%). CONCLUSIONS: The prostacyclin receptor antagonist RO3244019 decreased bladder contraction frequency and increased micturition threshold in the anesthetized isovolumetric bladder contraction and Refill models, respectively, and increased the micturition voiding interval in the conscious citric acid induced detrusor overactivity model. Additionally, RO3244019 remained effective for increasing the micturition threshold in the Refill model even following chronic capsaicin desensitization. Taken together these data suggest that prostacyclin may have a facilitory role in the micturition reflex by modulating the threshold for activation of capsaicin sensitive and insensitive bladder sensory afferents.

Purinoceptors as therapeutic targets for lower urinary tract dysfunction.

Lower urinary tract symptoms (LUTS) are present in many common urological syndromes. However, their current suboptimal management by muscarinic and alpha(1)-adrenoceptor antagonists leaves a significant opportunity for the discovery and development of superior medicines. As potential targets for such therapeutics, purinoceptors have emerged over the last two decades from investigations that have established a prominent role for ATP in the regulation of urinary bladder function under normal and pathophysiological conditions. In particular, evidence suggests that ATP signaling via P2X(1) receptors participates in the efferent control of detrusor smooth muscle excitability, and that this function may be heightened in disease and aging. ATP also appears to be involved in bladder sensation, via activation of P2X(3) and P2X(2/3) receptors on sensory afferent neurons, both within the bladder itself and possibly at central synapses. Such findings are based on results from classical pharmacological and localization studies in non-human and human tissues, knockout mice, and studies using recently identified pharmacological antagonists--some of which possess attributes that offer the potential for optimization into candidate drug molecules. Based on recent advances in this field, it is clearly possible that the development of selective antagonists for these receptors will occur that could lead to therapies offering better relief of sensory and motor symptoms for patients, while minimizing the systemic side effects that limit current medicines.