Pharmacologic evaluation of pressor and visceromotor reflex responses to bladder distension

AIMS: Several mechanisms that are involved in acute rat bladder nociception were examined. The nociceptive response was measured by analyzing both cardiovascular and visceromotor reflex responses to urinary bladder distension. The contributions of micro-opioid receptor, kappa-opioid receptor, sodium channels, muscarinic receptors, and cyclooxygenase, were explored with morphine, U50,488, mexiletine, oxybutynin, and naproxen, respectively. METHODS: Female Sprague-Dawley rats were acutely instrumented with jugular venous, carotid arterial, and bladder cannulas. Needle electrodes were placed directly into the abdominal musculature to measure myoelectrical activity subsequent to repeated phasic urinary bladder distension (60 mmHg for 20 sec in 3 min intervals) under 1% isoflurane. Drugs were administered by i.v. bolus injection 2 min prior to distension. RESULTS: The analgesics morphine (ID50 0.69 mg/kg), U50,488 (1.34 mg/kg), and mexiletine (2.60 mg/kg) significantly inhibited the visceromotor reflex response to noxious urinary bladder distension. Oxybutynin also attenuated reflex responses to noxious urinary bladder distension to 41% of the maximal pressor response and 32% of the control visceromotor reflex response (3.01 and 5.05 mg/kg), respectively, indicating a role of muscarinic receptors in bladder nociception. Naproxen did not attenuate the pressor response, but moderately inhibited visceromotor reflex to 45% of control at 30 mg/kg (P < 0.05). CONCLUSIONS: Current results using the rat urinary bladder distension model are consistent with previous research demonstrating a role of the analgesics (morphine, U50,488, and mexiletine) in the inhibition of visceral nociceptive transmission. The utility of the reflex responses to urinary bladder distension may provide a method useful to examine mechanisms which target the bladder sensory pathway.     

Effect of selective antagonists of group I metabotropic glutamate receptors on the micturition reflex in rats

OBJECTIVE

To investigate the role of Group I metabotropic glutamate (mGlu) receptor subtypes on reflex‐induced micturition in anaesthetized and conscious rats using selective mGlu1 (NPS 2407 and R214127) and mGlu5 (MPEP, MTEP, and SIB1893) allosteric antagonists.

MATERIALS AND METHODS

The affinity of the compounds at mGlu1 and mGlu5 receptor subtypes was evaluated by displacement of tritiated R214127 and MPEP, respectively, from rat brain tissue. Effects of intravenous (i.v.) administration of the compounds on isovolumic bladder contractions were evaluated in anaesthetized rats. Effects of MPEP and NPS 2407 on bladder filling and voiding were evaluated by cystometry using saline or diluted (0.2%) acetic acid (MPEP only) infusion of bladders in conscious rats.

RESULTS

Binding studies confirmed the selectivity of the mGlu1 (NPS 2407 and R214127) and mGlu5 (MPEP, MTEP, and SIB1893) compounds. Isovolumic bladder contractions were blocked after i.v. administration of all compounds. However, the mGlu5 antagonists were generally more potent than mGlu1 antagonists. In conscious rats with bladders infused with saline, MPEP dose‐dependently and significantly increased bladder capacity starting from oral administration of 10 mg/kg. Oral administration of NPS 2407 (up to 30 mg/kg) did not induce consistent changes in bladder capacity or micturition pressure. MPEP (10 mg/kg, orally) was also evaluated in conscious rats with bladders infused with diluted acetic acid. In this model, MPEP reduced bladder instability counteracting the decrease of bladder volume capacity induced by acetic acid. There were no consistent effects on bladder contractility.

CONCLUSIONS

The results indicate that i.v. and oral administration of selective mGlu5 antagonists, but not those selective for the mGlu1 subtype, have a marked inhibitory effect on reflex micturition pathways in the rat.     

Influence of temperature on urethra to bladder micturition reflex in the awake ewe

AIMS: The flow of fluid along the urethra is known to facilitate detrusor contraction during micturition. This reflex, previously described in awake ewes, helps to achieve complete bladder emptying. In anesthetized cats, another urethra to bladder reflex involving urethral cold receptors has been described. The aim of this study was to investigate whether the urethral reflex first described in awake ewes could also be temperature-dependent. METHODS: Experiments were performed on 10 healthy ewes. Urethral flows were performed by injecting 10 ml saline (ranging from 17 to 43 degrees C) at the level of the proximal urethra. Catheterization of the bladder was performed so that detrusor pressure was continually recorded during the experiments. RESULTS: Urethral flows using body temperature saline (37-39 degrees C) consistently evoked detrusor contraction. Urethral flows using saline at temperatures between 40 and 43 degrees C induced detrusor contractions that were not significantly different from those observed at 37-39 degrees C. Urethral flows using saline at temperatures below 37-39 degrees C (17-36 degrees C) resulted in a weaker or absent detrusor contraction. CONCLUSIONS: In ewes, we have shown that urethral to bladder micturition reflex involving mechanoreceptors is decreased at temperatures below the physiological range. It is suggested that transient receptor potential vanilloid cation channels (e.g., TRPV4 which is activated by sheer/stress flows at near-body temperature) could be involved in this urethra to bladder reflex. In humans, this reflex has hardly been described and is still a matter of debate. Our results reinforce that its full investigation may require systematic use of a range of saline flows at different temperatures.     

Outcome of the bladder cooling test in children with nonneurogenic bladder problems

PURPOSE: The bladder cooling test (BCT) engages a primitive neonatal spinal reflex that becomes suppressed by descending signals in older children and may reappear with suprasacral lesions. We assessed the outcome of the BCT in a large group of children with nonneurogenic bladder problems. MATERIALS AND METHODS: The BCT was evaluated in a consecutive series of 178 girls and 106 boys, 1 month to 18 years old with bladder problems without overt neurology. The test was performed at the end of routine cystometry by a rapid control infusion of body warm saline followed, after fluid evacuation, by the same volume of cold saline (3 to 10C). The test was considered positive if a detrusor contraction greater than 30 cm H2O was evoked by the cold but not the warm fluid. RESULTS: Most children younger than 4 years had a history of pyelonephritis (29 of 34) and/or had vesicoureteral reflux (grade IV to V in 26 of 34). For those younger than 2 years 87% of the BCTs were positive while only 21% of the tests were positive in 2 to 3-year-old children. Most children older than 4 years had idiopathic urge incontinence, and greater than 50% of the BCTs were positive in the youngest (less than 6 years) with a gradual decline to 0% at age 13 years. CONCLUSIONS: Conversion of positive to negative BCTs at about age 2 years presumably represents normal maturation while positive tests in older incontinent children suggest delayed maturation of the central neuronal control of the bladder.     

Effects of glucose deprivation on the contractile response of the rabbit bladder to repetitive stimulation

The urinary bladder requires an adequate energy supply to maintain contractile function. The primary metabolic fuel is glucose. Through glycolysis and oxidative phosphorylation, high energy phosphates are generated, which in turn supply the metabolic energy for the contractile activities of the urinary bladder. The aim of this study was to determine the effects of glucose deprivation and recovery from glucose deprivation on the phasic and tonic components of the contractile responses of rabbit bladder strips to field stimulation, bethanechol, and KCI. The results can be summarized as follow: In response to glucose deprivation, (1) the tonic responses to field stimulation, bethanechol, and KCI all decreased at a significantly greater rate than the phasic responses; (2) the phasic and tonic responses to field stimulation were both reduced to less than 10% of control within 70 minutes of initiating glucose deprivation; (3) the tonic responses to bethanechol and KCI were reduced to approximately 10% of control within 180 minutes whereas the phasic responses remained stable at 40 and 30%, respectively; and (4) glucose replacement stimulated a rapid and nearly complete recovery of the phasic and tonic components of the responses to field stimulation, bethanechol, and KCI. These results indicate that the tonic responses to all forms of stimulation are more sensitive to glucose deprivation than the phasic responses. © 1996 Wiley-Liss, Inc.     

Increased maternal intraabdominal pressure alters the contractile properties of fetal rabbit bladder

Background/Purpose

Increased intraabdominal pressure (IAP) causes impairment of urine flow by compressing the urine-transporting structures and leads to development of various types of anatomical and functional abnormalities in the urinary system. An intrauterine experiment was conducted to determine the relationship between IAP and intraamniotic pressure (IAMNP) and the effects of increased IAMNP on the contractile properties of fetal bladder in the rabbit model.

Materials and Methods

Fourteen time-mated pregnant rabbits were used. A preliminary study (n = 5, 20-day gestation) was performed to determine the relation between IAP and IAMNP. Intraabdominal pressure and IAMNP were recorded through an intraperitoneal catheter and 2 intraamniotic transducers, respectively. Basal IAP and IAMNP were recorded. Then, IAP was increased for 4 cm H₂O in each subsequent 30-minute period until reaching 20 cm H₂O. Control (n = 5) and experiment (n = 4) group animals underwent intraperitoneal catheter placement in the 15th day of gestation. Intraabdominal pressure was increased by intraperitoneal air insufflations from 20th day to term in the experiment group. At term, the fetal bladders were excised and the contractile activity was then recorded isometrically. Electrical field stimulation was applied, and contractile responses to carbachol and high potassium (20 mmol/L KCl) were also evaluated.

Results

A strong relationship was found between IAMNP and IAP and defined as IAMNP = IAP × 0.8 + 2.0 (R² = 0.816, P = .000). Increased IAP did not change basal rhythmic activity but resulted in frequency-related electrical field stimulation responses being higher contractility responses for frequencies below 10 Hz (P < .05) and similar responses at and above 10 Hz. Bladders imposed to elevated IAP displayed greater sensitivity to carbachol with a shift to the left in the concentration-response curve. High potassium-induced contractions had a shorter rise time (P < .05) but similar contraction amplitudes and half decay times in bladders imposed to increased IAP.

Conclusion

Intraamniotic pressure is affected by IAP in pregnant rabbits in accordance with an equation (IAMNP = IAP × 0.8 + 2.0). Increased IAMNP changes contractile properties of the fetal rabbit bladder without affecting spontaneous activity and shortens the rise time of high potassium-induced contractions. Increased IAMNP also results in cholinergic hypersensitivity in fetal bladders. These results may explain the mechanism of dysfunctional voiding and abnormal bladder function observed in conditions in which IAP and/or IAMNP are elevated.     

Autonomous contractile activity in the isolated rat bladder is modulated by a TRPV1 dependent mechanism

AIMS: Resiniferatoxin (RTX), a vanilloid compound and agonist of the transient receptor potential channel 1 (TRPV1), is known for its beneficial effects on neurogenic detrusor overactivity. The mainstream rationale for its use is the desensitization of TRPV1 on sensory bladder afferents. However, recent findings showed that TRPV1 is present in other cell types in the bladder. To eliminate the effects of RTX on spinal and central neural circuits, we investigated autonomous contractility in normal and neurogenic rat bladders after treatment with RTX. METHODS: Female Wistar rats were made paraplegic at vertebral level T8-T9. Animals were intravesically pre-treated with vehicle (ethanol 5%) or RTX (100 nM) and sacrificed after 72 hr. Each bladder was excised and placed in a heated organ bath, where intravesical pressures were measured. Effects on contractile parameters of intravesical volume load, the non-selective muscarinic receptor agonist carbachol (CA) and electrical stimulation (ES) of nerves were studied in both groups. RESULTS: In RTX-treated normal bladders we found shorter contractions with higher amplitude than in control bladders (P < 0.05). In RTX-treated neurogenic bladders the amplitude and duration of autonomous contractions were increased compared with controls (P < 0.05). Furthermore RTX induced an increased response to CA and to ES (P < 0.05). CONCLUSIONS: RTX significantly affected the properties of autonomous bladder contractile activity. This provides evidence for local effects of RTX on bladder contractile activity, which are not mediated by afferent neural pathways and which may contribute to the beneficial effects on detrusor overactivity. TRPV1 and TRPV1(+) cells seem to play an important role in (autonomous) bladder contractility.     

Effect of urethral dilation on vesical motor activity: identification of the urethrovesical reflex and its role in voiding

PURPOSE: We investigated the hypothesis that mild urethral distention, which presumably occurs during the passage of urine through the urethra, stimulates stretch receptors in the urethral wall, leading reflexively to vesical contraction. MATERIALS AND METHODS: We evaluated 9 male and 10 female healthy volunteers with a mean age +/- SD of 39.6 +/- 8.3 years. The posterior urethra was distended by a balloon filled with saline in 1 ml. increments up to 6 ml., while recording vesical pressure. The test was repeated after individual anesthetization of the urethra and bladder. RESULTS: Vesical pressure increased significantly at 1 and 2 ml. urethral distention (p <0.01). Increases in urethral distention effected further vesical pressure elevation (p <0.001), although there was no significant difference in distention at 3 to 6 ml. (p >0.05). No significant vesical pressure response of the individually anesthetized urethra or bladder occurred during urethral distention. CONCLUSIONS: Urethral distention is thought to cause vesical contraction through the stimulation of urethral stretch receptors. Vesical contraction at urethral distention postulates a reflex relationship that was abolished by individual anesthetization of the urethra and bladder. This relationship, which we call the urethrovesical reflex, appears to have a role in maintaining vesical contraction during voiding. Further studies are required to investigate the role of this reflex in voiding disorders.     

人工体神经-内脏神经反射弧治疗脊髓脊膜膨出患者大小便功能障碍

目的 :建立“人工体神经 内脏神经反射弧”(简称人工反射弧 )治疗脊柱裂脊髓脊膜膨出患者大小便功能障碍。方法 :对 30例大小便功能障碍的脊髓脊膜膨出患者 ,手术建立人工反射弧。进行术前与术后 6～ 1 8个月的尿动力学比较。结果 :30例中 1 3例获得了至少 1年的随访。 7例无反射型患者中 4例获得控尿和自主排尿功能 ,尿失禁消失 ,排尿间隔期逐渐延长至 3h以上 ,逼尿肌压由 (1 .37± 0 .78)kPa(1kPa =0 .0 98cmH2 O)增至(3.1 4± 1 .6 7)kPa ;6例高反射型患者全部于术后 1年左右恢复可控排尿 ,剩余尿逐渐减至 (2 2± 1 5 )ml,充盈性尿失禁消失。 1 0例获得膀胱功能控制者 ,直肠功能转为基本正常。下肢功能损伤较小。结论 :人工反射弧能安全有效地治愈先天性脊髓脊膜膨出所致大小便失禁     

Urodynamic studies in the rabbit under the immobility reflex

We studied some urodynamic (UD) parameters in normal rabbits under immobility reflex (IR), without anesthesia. These parameters were compared after induction of anesthesia. We found that anesthesia had a depressing effect on these UD parameters. IR is a good method for studying rabbits without the effect of anesthesia.     

The effect of hexamethonium on the distension-induced contractile activity of the rat bladder: Evidence for the existence of a spinal ‘short-loop’ vesicovestioal reflex in rats

Saline distension of the bladder in urethane-anaesthetized rats elicited three types of phasic contractions: (a) a low amplitude (<4 mmHg) asynchronous contractile activity which is hexamethonium-resistant; (b) an intermediate amplitude (8–16 mmHg) rhythmic contractile activity that was still present in spinal (C2-C3) rats and was eliminated by hexamethonium; and (c) a high amplitude (>20 mmHg) rhythmic contractile activity that was eliminated by spinal cord transection or hexamethonium. All types of hexamethonium-sensitive rhythmic contractile activity having an amplitude higher than 4–6 mmHg were prevented by destruction of the lumbosacral spinal cord. It is concluded that in adult rats two distinct types of vesicovesical reflex activity organized at spinal and supraspinal level, respectively, could be elicited by distension at a physiological-like filling rate.     

兔膀胱5—氟尿嘧啶微球化学栓塞的实验研究

采用以５－氟尿嘧啶、人血清白蛋白为材料制成的微球，注入实验兔髂内动脉、测定髂内动注入微球后的血药浓度及膀胱组织药物浓度。同时对５只兔以同法注入等量常规５－Ｆｕ作为对照。结果：制成的微球直径３５－７５μｍ，含药量均为１０％。     

Effect of nicotine on the pelvic afferent nerve activity and bladder pressure in rats

Objectives:   To record afferent nerve activity and bladder pressure in anesthetized male rats and to investigate whether increased afferent nerve activity induced by nicotine is able to evoke reflex bladder contractions.
Methods:   Using continuous infusion cystometrography, bladder pressure was measured via a bladder cannula. Afferent activity was recorded in the uncut L6 dorsal root. Nicotine was injected intra-arterially through a cannula placed near the bifurcation of the internal iliac artery a few minutes after micturition.
Results:   Nicotine (0.15–1.5 µmol) evoked a marked elevation of afferent discharge without a simultaneous increase in bladder pressure. Bladder contractions appeared about 43 and 19 s after bolus injection of nicotine at 0.45 and 1.5 µmol, respectively. Firing rates of afferent nerves were reduced when the contraction appeared. Continuous infusion of nicotine at 0.75 µmol/min for 20 min evoked marked elevation of afferent discharge, which was maintained during infusion of nicotine and after it had been withdrawn. Repetitive contractions were observed thereafter and disappeared when the L6 dorsal roots were bilaterally resected.
Conclusions:   A transient increase in afferent discharges induced by bolus injection of nicotine was unable to evoke reflex bladder contraction. Repetitive bladder contractions after withdrawal of continuous nicotine infusion were induced in a reflex manner by the increased afferent activity.     

Effects of potassium channel modulators on myogenic spontaneous phasic contractile activity in human detrusor from neurogenic patients

OBJECTIVE

To characterize the spontaneous contractile activity (SCA) developed by detrusor from patients with neurogenic detrusor overactivity (NDO) because the alteration of detrusor properties plays a critical role in the pathogenesis of detrusor overactivity, as well as to evaluate the role of K_ATP and K_Ca channels on this SCA because these channels regulate detrusor SCA in many species, including humans without overactive bladder (OAB).

PATIENTS AND METHODS

Human bladder samples were obtained from 44 patients undergoing cystectomy for bladder cancer with no known OAB symptoms and from 38 patients suffering from urodynamically diagnosed NDO. Detrusor strips with or without urothelium/suburothelium were mounted isometrically in organ baths filled with Krebs‐HEPES (37 °C; 95% O₂/5% CO₂). Strips were incubated with 10 µm pinacidil (K_ATP opener) followed by 10 µm glibenclamide (K_ATP blocker). In another set of experiments, strips were incubated with 30 µm NS‐1619 (BK_Ca opener) followed by 100 nm iberiotoxin (BK_Ca blocker) or with 100 nm apamin (SK_Ca blocker).

RESULTS

SCA occurred more frequently with larger amplitude and area under the curve in detrusor strips from NDO patients compared to control patients. The presence of urothelium/suburothelium did not significantly modify SCA in either patient population. Pinacidil markedly inhibited SCA of detrusor strips from control and NDO patients. This effect was reversed by glibenclamide. By contrast, NS‐1619 followed by iberiotoxin did not elicit any significant changes in SCA from NDO patients, contrary to control patients.

CONCLUSIONS

K_ATP and SK_Ca channels regulate SCA of NDO patients’ detrusor strips. By contrast, BK_Ca channels are not involved in the regulation of detrusor SCA in NDO patients, whereas they regulate SCA in control patients. These results should be considered in the development of K⁺ channels openers for the treatment of NDO. Moreover, SCA observed in vitro should be regarded as an in vitro modelling of human NDO.     

Effect of ischemia of the rabbit bladder on Ca-Mg-activated ATP-ase activity

This investigation is concerned with the effect of ischemia on the activity of Ca-Mg-stimulated ATP-ase in rabbit bladder tissue. White New Zealand male rabbits were used for the experiments. Ischemia was produced by clamping of the vesical arteries. After 1 and 2 hours the clamps were removed, and the animals were sacrificed 2 days later. The bladders were removed, and the muscle and mucosal parts of the bladders were separated. In some experiments with 2-hour ischemia the animals were allowed to recover for 7 days. Homogenates were made of the muscle and mucosal tissue and separated by differential centrifugation into three parts: 1) an initial particulate fraction obtained by low-speed centrifugation; 2) a supernate fraction free of mitochondria; and 3) a mitochondrial-rich fraction. ATP-ase activity was determined in the different fractions in the presence of magnesium or calcium as the activating ion, and the results were expressed as nmols/mg protein/minute. The following results were obtained: with the supernates, ischemia was found to produce a marked inhibition of enzyme activity that was large and significant in muscle tissue after 1 hour and in mucosal tissue after 2 hours. Seven days after termination of 1 hour of ischemia, the ATP-ase activity of the muscle fraction had been partially restored towards normal. Activity of ATP-ase when measured in the particulate fraction was less sensitive to the effect of ischemia; a significant diminution of enzyme activity in preparations from muscle was seen only after 2 hours of ischemia, and no inhibition was observed with mucosal tissue. ATP-ase of muscle mitochondria was severely inhibited by ischemia, and the effect of 1 hour of ischemia was not reversed 7 days after the insult. Mitochondria from mucosal tissue were affected to only a small extent by ischemia. In all cases, results were similar whether magnesium or calcium was used for activation of the enzyme. © 1996 Wiley-Liss, Inc.     

Sympathetic inhibition of reflex activation of bladder motility during filling at a physiological-like rate in urethane anaesthetized rats

The mean volume of saline (infused at a physiological-like rate) required to elicit neurogenic rhythmic contractions of the detrusor muscle (micturition threshold) in urethane anaesthetized rats was reduced by reserpine pretreatment, as well as by chemical (6-hydroxydopamine) or surgical sympathectomy (bilateral section of the hypogastric nerves). Propranolol pretreatment had no significant effect on micturition threshold but increased the intraluminal pressure at which the rhythmic contractions occurred. In spinal rats (T12L1) a flat pressure volume curve was obtained with only a minor phasic contractile activity. Propranolol administration or bilateral section of the hypogastric nerves significantly increased the intraluminal pressure response to saline filling in spinal rats. Topical tetrodotoxin increased the intraluminal pressure response to saline filling in control spinal rats but not following propranolol administration or bilateral section of the hypogastric nerves. These findings provide evidence for a sympathetic inhibition of the reflex activation of the detrusor muscle in response to a physiological-like filling of the urinary bladder.     

Spontaneous contractions of the pig urinary bladder: the effect of ATP-sensitive potassium channels and the role of the mucosa

OBJECTIVE

To investigate the influence of the mucosa on the inhibitory effects of the ATP‐sensitive potassium channel (K_ATP channel) opener, cromakalim, on the spontaneous contractions of pig bladder strips from the bladder dome and trigone. Little is known about the influence of the mucosa on spontaneous contractions and whether the nature of these contractions differs between the bladder dome and trigone.

MATERIALS AND METHODS

Paired longitudinal strips of female pig bladders were isolated from the dome and trigone. The mucosa was removed from one strip per pair and tissues were set up in organ baths. Spontaneous activity was allowed to develop and recorded, and then cumulative concentration–response curves to cromakalim were obtained. The time needed for spontaneous contractions to develop, the frequency and amplitude of spontaneous contractions, and the effect of cromakalim were analysed. The strips of mucosa removed from the dome to produce denuded strips were also analysed by immunofluorescence using antibodies specific for vimentin and α‐smooth muscle actin (α‐SMA).

RESULTS

In the dome removal of the mucosa delayed the development of spontaneous contractions compared with mucosa‐intact strips, whilst the trigone strips developed spontaneous contractions soon after set up in the organ baths irrespective of the presence or absence of mucosa. In the dome, cromakalim was more potent in suppressing spontaneous contractions when the mucosa was absent; whilst in the trigone the effects of cromakalim were similar in mucosa‐intact and denuded strips. Upon examination of the strips of mucosa by immunofluorescence these strips were shown to contain cells positive for α‐SMA or vimentin and cells positive for both, suggesting the presence of not only urothelium but also suburothelium and some detrusor smooth muscle bundles.

CONCLUSION

In the dome, the urothelium and suburothelium reduce the inhibitory effect of cromakalim on spontaneous contractions, whilst in the trigone these structures appear to have little influence. The mechanism for generating spontaneous contractions in the intact strips seems to be linked to the urothelium and suburothelium in the dome but not in the trigone.