Effect of bladder outlet obstruction on the morphology, physiology, and pharmacology of the bladder

Obstruction-induced changes in urinary bladder smooth muscle contractility: a role for Rho kinase

Detrusor smooth muscle (DSM) undergoes hypertrophy after partial bladder outlet obstruction (PBOO) in male rabbits, as it does in men with PBOO induced by benign prostatic hyperplasia. Despite detrusor hypertrophy, some bladders are severely dysfunctional (decompensated). In this study, the rabbit model for PBOO was used to determine the biochemical regulation of the contractile apparatus and force maintenance by the detrusor from decompensated bladders (DB). Bladders from sham-operated rabbits served as a control. On stimulation with 125 mM KCl, the DSM from sham-operated (SB) rabbits showed phasic contractions, whereas the detrusor from DB was tonic, exhibiting slow development of force, a longer duration of force maintenance, and slow relaxation. The Rho kinase (ROK) inhibitor Y-27632 enhanced the relaxation of precontracted DSM strips from DB. The enhancement of relaxation of the KCl-induced contraction of DB by Y-27632 was associated with dephosphorylation of myosin light chain (MLC20). The DSM extract from DB showed low phosphatase activity compared with that from SB. The DB also showed more Ca2+-independent MLC20 phosphorylation, which was partially inhibited by Y-27632. RT-PCR and Western blotting revealed similar expression levels of MLC kinase and ROK-alpha in SB and DB, but ROK-beta was overexpressed in DB. These results suggest that the ROK-mediated pathway is partly responsible for the high degree of force maintenance and slow relaxation in the detrusor from DB.

Bladder wall tension during physiological voiding and in patients with an unstable detrusor or bladder outlet obstruction

OBJECTIVE

To develop and evaluate a new clinical method for measuring bladder wall tension (BWT) on detrusor contraction during physiological voiding and under pathological conditions, as in experimental trials during subvesical obstruction the ability to generate pressure increases, whereas the contractile force per cross-sectional area of detrusor muscle decreases.

PATIENTS AND METHODS

In all, 24 patients were divided into three equal groups: group 1 (mean age 58, sd 8.6 years) comprised men with bladder outlet obstruction in accordance with the Abrams-Griffiths nomogram; group 2 (four men and four women, 56, sd 7.2 years) had detrusor instability; and group 3 (54, sd 9.6 years) had normal bladder emptying. BWT, as the detrusor force per cross-sectional area of bladder tissue (in N/cm2), was calculated after a urodynamic evaluation and ultrasonographic estimate of bladder wall thickness.

RESULTS

In all patients it was possible to measure BWT; the mean (sd) maximum BWT in group 1 was 9.8 (3.9) N/cm2, in group 2 during bladder instability was 11.7 (2.6) N/cm2 and in group 3 was 2.8 (0.5) N/cm2.

CONCLUSIONS

Estimating BWT in humans is possible by combining a urodynamic evaluation with an ultrasonographic estimate of bladder wall thickness. Further clinical research should elucidate the clinical relevance of BWT under comparable conditions.

Analysis of hydrostatic pressure-induced changes in umbrella cell surface area

All cells experience and respond to external mechanical stimuli including shear stress, compression, and hydrostatic pressure. Cellular responses can include changes in exocytic and endocytic traffic. An excellent system to study how extracellular forces govern membrane trafficking events is the bladder umbrella cell, which lines the inner surface of the mammalian urinary bladder. It is hypothesized that umbrella cells modulate their apical plasma membrane surface area in response to hydrostatic pressure. Understanding the mechanics of this process is hampered by the lack of a suitable model system. We describe a pressure chamber that allows one to increase hydrostatic pressure in a physiological manner while using capacitance to monitor real-time changes in the apical surface area of the umbrella cell. It is demonstrated that application of hydrostatic pressure results in an increase in umbrella cell apical surface area and a change in the morphology of umbrella cells from roughly cuboidal to squamous. This process is dependent on increases in cytoplasmic Ca(2+). This system will be useful in further dissecting the mechanotransduction pathways involved in cell shape change and regulation of exocytic and endocytic traffic in umbrella cells.

Effectiveness of vaginally administered oxybutynin on rabbit bladder function

OBJECTIVES

To demonstrate the effectiveness of vaginally delivered oxybutynin on bladder function. Oxybutynin has been used for treatment of urge urinary incontinence for more than 20 years.

METHODS

Thirty female New Zealand White rabbits were used for this experiment. Each rabbit was anesthetized, and the carotid artery was cannulated for blood pressure monitoring. The bladder dome was catheterized for both monitoring of bladder pressure and cystometry. After initial cystometry, acetylcholine (ACh) was injected into the vesical artery at 15-minute intervals for 4 hours. Cystometry was performed at the 2-hour mark and at the end of each experiment (4 hours). After the third ACh administration, vaginal or oral oxybutynin was given and the effect on the response to ACh, blood pressure, and cystometry was observed.

RESULTS

The high dose of oxybutynin completely inhibited the response to ACh and significantly inhibited the micturition reflex. A 45% inhibition of micturition pressure occurred at the intermediate dose. Little effect on compliance after the low dose and a significant increase in compliance after the mid-dose occurred. Both the low and intermediate doses of oxybutynin reduced the response to ACh to approximately 50% of control. No blood pressure effects of vaginal oxybutynin were noted for any concentration. Oral oxybutynin showed very similar effects to that of the intermediate vaginal dose.

CONCLUSIONS

Vaginally delivered oxybutynin was effective in decreasing bladder compliance and inhibiting intra-arterial ACh-stimulated bladder contractions with little or no effect on the vascular effect of ACh.

Inducible nitric oxide synthase promotes pathophysiological consequences of experimental bladder outlet obstruction

PURPOSE

Bladder outlet obstruction leads to histological and functional changes in the bladder over time. We investigated the role of inducible nitric oxide synthase (iNOS) in the progression of pathological changes of the bladder secondary to outlet obstruction in a rat and a mouse model.

MATERIALS AND METHODS

To assess expression of iNOS in the bladder, polymerase chain reaction amplification of mRNA was done. Rats were subjected to sham operation or partial bladder outlet obstruction. They were given the iNOS inhibitor aminoguanidine in drinking water or unmodified water. After 2 weeks, awake cystometric evaluation was performed, the bladders were harvested and the degree of fibrosis was assessed. In another series of experiments mice deficient in the iNOS gene (iNOS -/-) were compared to WT mice for cystometric as well as histological changes in the bladder following partial bladder outlet obstruction or sham operation.

RESULTS

Partial bladder outlet obstruction induced the expression of iNOS mRNA in the mouse bladder. iNOS -/- mice showed a significantly smaller increase in bladder volume at 3 weeks compared with WT. Pharmacological inhibition of iNOS activity significantly attenuated the increase in bladder size and the number of spontaneous bladder contractions in obstructed rats at 2 weeks. Furthermore, genetic and pharmacological decreases in iNOS led to significantly less fibrosis of the bladder after partial bladder outlet obstruction in mice and rats, respectively.

CONCLUSIONS

Pharmacological or genetic decreases in iNOS resulted in amelioration of functional and fibrotic changes in the bladder after partial bladder outlet obstruction, suggesting that NO contributes to the pathophysiology of bladder outlet obstruction.

Preoperatively evaluated bladder wall tension as a prognostic parameter for postoperative success after surgery for bladder outlet obstruction

OBJECTIVES

To evaluate a novel method for the determination of bladder wall tension (BWT) and to correlate these findings with postoperative persistent residual urine, postoperative uroflow, International Prostate Symptom Score, and quality-of-life index in patients with bladder outlet obstruction.

METHODS

In 28 male patients with prostate enlargement or bladder neck sclerosis undergoing surgical treatment, the preoperative BWT was determined after urodynamic investigation and ultrasound determination of bladder weight. The patients were divided into two groups: group 1 (n = 24), postoperative residual urine volume less than 50 mL; and group 2 (n = 4), persistent residual urine volume greater than 50 mL. Five patients in group 1 were unobstructed in accordance with the Abrams-Griffiths nomogram. This group was compared separately with group 2, in which all 4 patients were also classified as unobstructed.

RESULTS

The preoperative BWT in group 1 was 5.2 +/- 4.1 N/cm(2), significantly different from the preoperative BWT in group 2 (0.98 +/- 0.3 N/cm(2)). The BWT in the 5 unobstructed patients in group 1 (3.4 +/- 1.3 N/cm(2)) was significantly greater than that in patients in group 2. BWT was the sole parameter that was distinctly different between these 5 patients and the patients in group 2, with a significant influence on postoperative uroflow, International Prostate Symptom Score, and quality-of-life index.

CONCLUSIONS

The results of this pilot study show that the determination of BWT allows further evaluation of the detrusor function. Especially in patients classified as unobstructed according to the Abrams-Griffiths nomogram, preoperative determination of the BWT could become a supplemental and important parameter with predictive value for postoperative success in patients with prostate enlargement or bladder neck sclerosis.

Comparison of parameters to determine the cause of urinary disturbance in men with prostate volume less than 20 milliliters

BACKGROUND

A pressure-flow study, although a slightly invasive procedure, can evaluate bladder outlet obstruction and detrusor contractility. This study was conducted in men with a non-enlarged prostate to determine the cause of urinary disturbance by less invasive examinations that might eventually replace pressure-flow study.

METHODS

Thirty-six men with lower urinary tract symptoms were enrolled. Their prostate volume, estimated by transrectal ultrasonography, was less than 20 mL. All patients were examined using pressure-flow study, free-flowmetry, transrectal ultrasonography, prostate specific antigen and an interview using the International Prostate Symptom Score and Quality of Life Index. With determination of the cause for urinary disturbance, parameters that correlated with outflow obstruction or impaired detrusor contractility were sought.

RESULTS

Twenty-one (60%) of the 36 men were judged as having outflow obstruction, and 16 of these 21 men had normal detrusor function. Impaired detrusor contractility was observed in 17 men. Only three of these 17 men had no outflow obstruction. Four patients had an unstable bladder. All these four had normal detrusor contractility, but had outflow obstruction. Among the parameters examined, only the maximum flow rate in a flow metrogram (Qmax) correlated significantly with the degree of outflow obstruction (P = 0.04). The positive predictive value of Qmax for outflow obstruction was 65% at a flow rate of less than 10 mL/s, and 100% at that of less than 5 mL/s. No parameter correlated with detrusor contractility.

CONCLUSION

The only parameter that was a clear indicator of outflow obstruction was Qmax. Other indicators of detrusor contractility should be sought.

Relationship of mass of obstructed rat bladders and responsiveness to adrenergic stimulation

PURPOSE

The effects of experimental partial bladder outlet obstruction on the bladder response to nerve stimulation and contractile agonists have been well characterized. Mildly obstructed bladders have small increases in mass and increased contractile responses to electrical field stimulation. More severely obstructed bladders become decompensated with large increases in mass and decreased functional responses. Little is known about relaxant mechanisms after obstruction. We investigated the relationship of the increase in rat bladder mass induced by outlet obstruction and responses to alpha and beta-adrenergic stimulation.

MATERIALS AND METHODS

Male Sprague-Dawley rats were divided into 3 groups, namely control, sham operated and obstructed. Surgical obstruction was done by tying a 2-zero silk ligature around the urethra. The ligature was placed around the urethra and removed in sham operated rats. At 2 and 6 weeks bladders from all groups were harvested, weighed and cut into strips. Contractile responses to electrical field stimulation and norepinephrine in the presence of propranolol were measured. Relaxant responses to norepinephrine and isoproterenol were measured after pre-contraction with KCl.

RESULTS

All strips from control and sham operated rats relaxed completely in response to norepinephrine. Obstructed bladders that weighed 2 to 3-fold more than control or sham operated bladders also relaxed. In contrast, bladders that were 5 to 10-fold heavier failed to relax by at least 50% in response to norepinephrine, independent of duration of bladder outlet obstruction. These were called nonresponders. Two week nonresponders relaxed completely in response to isoproterenol, but 6-week nonresponders did not, suggesting that the duration of decompensation is important. All nonresponders relaxed in response to pinacidil (Sigma-Aldrich Corp., St. Louis, Missouri). Nonresponders tended to contract in response to norepinephrine in the presence of propranolol. Strips from the other rats were less responsive, suggesting an increase in alpha1-receptors with decompensation. Contractile responses to field stimulation were increased in obstructed strips that relaxed to norepinephrine, while responses of nonresponders were decreased compared with controls and sham operated rats.

CONCLUSIONS

Severely obstructed bladders had an increase in mass and a decreased response to field stimulation, indicative of decompensation. This response was accompanied by decreased ability to relax to beta-agonists and an increased response to alpha-agonists. These changes were not seen in smaller, compensated bladders. Our findings suggest a change in detrusor alpha1 and beta-adrenergic receptor density. An increase in detrusor alpha-receptors may explain the clinical efficacy of alpha-blockers in alleviating irritative voiding symptoms in men with benign prostatic hyperplasia.

The aging bladder--a significant but underestimated role in the development of lower urinary tract symptoms

There are three major areas in which bladder dysfunction causes considerable losses in quality of life: detrusor instability, impaired detrusor function and detrusor reaction on bladder outlet obstruction. Considerable changes in detrusor morphology, detrusor innervation and bladder metabolism are seen with aging and obstruction. This causes dysfunction and lower urinary tract symptoms. The relation between aging per se and external influence on the detrusor from diseases in the nervous system, in the vascular supply and in the lower urinary tract itself is poorly understood. To improve our ability to prevent and treat these conditions we need more insight in these pathophysiological conditions.

Hypoxia and an angiogenic response in the partially obstructed rat bladder

Previous molecular and blood flow studies performed on animal models of partial bladder outlet obstruction (PBOO) caused us to propose that bladder hypoxia/ischemia was a significant effector of the cellular and functional changes that occur in the bladder as a result of this condition. To confirm the occurrence of hypoxia in the partially obstructed bladder, we obtained rat bladders at increasing intervals following PBOO and measured biomarkers of hypoxia (intracellular formation of hypoxyprobe-1 adducts and expression of hypoxia inducible factor-1 alpha [HIF-1 alpha] protein) and whether such hypoxia might elicit an angiogenic response in the tissue. Rats receiving PBOO or controls were treated with hypoxyprobe-1 at increasing intervals subsequent to surgery and their bladders were sectioned and immunostained using an antibody that detects hypoxyprobe-1 adducts. Control rat bladders were unstained, whereas intense, but regionally restricted, hypoxyprobe-1 immunostaining was detected in all obstructed bladders in a unique pattern that changed over time. Proteins were extracted from bladders removed from similarly treated rats and were analyzed for the expression of the HIF-1 alpha protein as well as for expression of angiogenic regulatory factors (vascular endothelial growth factor, angiopoietin-1, and endostatin) using Western blotting techniques. HIF-1 alpha protein was not expressed in control bladders, however, the protein was highly up-regulated over the 2-week period after PBOO. Likewise, the expression of vascular endothelial growth factor (a downstream target of HIF-1 alpha action) and angiopoietin-1 was also up-regulated in obstructed bladders confirming an angiogenic response to this hypoxia. Enigmatically, however, expression of the antiangiogenic molecule endostatin was also up-regulated by chronic PBOO. These results further support the concept that hypoxia is involved in the cellular remodeling as well as in the progressive functional impairment exhibited by the urinary bladder after PBOO.

Effect of doxazosin on rat urinary bladder function after partial outlet obstruction

Hypoxia induced by partial outlet obstruction is believed to play a major role in both the hypertrophic and degenerative effects of partial outlet obstruction. Doxazosin (dox) is a clinically effective alpha-adrenergic antagonist used in the treatment of symptomatic benign prostatic hyperplasia (BPH). Although the major therapeutic effect of the agent is believed to occur on the smooth muscle components of the prostate by reducing prostatic urethral resistance and thus improving emptying, dox may have part of its clinical action via effects mediated by other actions, including via spinal alpha-adrenergic receptors or direct effects on the bladder, possibly via inhibition of vascular alpha receptors. The specific aim of the current study was to determine whether dox pretreatment on rats affects blood flow to the bladder and reduces the level of bladder dysfunction induced by partial outlet obstruction. In part 1, eight rats were separated into two groups of four rats each. Group 1 received oral administration of dox (30 mg/kg) for 4 weeks; group 2 received vehicle (5% dimethyl sulfoxide). After 4 weeks of treatment, blood flow studies were performed using fluorescent microspheres and the bladders excised, frozen, and submitted to Interactive Medical Technologies (IMT) for blood flow analysis. In part 2, 32 adult male rats were separated into four groups of eight rats each. Groups 1 and 2 received oral administration of dox (30 mg/kg) for 4 weeks, groups 3 and 4 received vehicle (5% dimethyl sulfoxide). At 4 weeks, the rats in groups 1 and 3 received partial outlet obstructions and treatment continued for an additional 2 weeks. After 6 weeks of treatment (total), each rat was anesthetized, the bladder excised, weighed, and isolated strips mounted and contractility studies performed. 1) Four weeks pretreatment of rats with dox increased blood flow to the bladder in both the control and obstructed groups. 2) Partial outlet obstruction induced a mild decrease in blood flow. 3) The magnitude of the increased bladder weight in the vehicle-treated obstructed group was significantly greater than in the dox-treated obstructed group. 4) Partial outlet obstruction resulted in significant decreases in the contractile response to field stimulation in both treated and non-treated rats. The magnitude of the decreased response was significantly greater in the non-treated rats. 5) The response to potassium chloride was significantly reduced by partial outlet obstruction in the vehicle-treated group but not in the dox-treated group. 6) The time to maximal tension was significantly increased in response to carbachol, adenosine triphosphate, and potassium chloride. However, the magnitude of the increase was significantly greater for the vehicle-treated obstructed groups stimulated by potassium chloride than for the dox-treated groups. Dox treatment of rats increased blood flow to the bladder and reduced the severity of the response to partial outlet obstruction. These beneficial effects would be due to pharmacological effects on alpha-adrenergic systems outside those present in the prostate. These include effects on blood flow to the bladder, effects on the micturition centers of the central nervous system, spinal reflexes, and alpha-adrenergic receptors in the urethra and bladder.

A method for estimating within-patient variability in maximal urinary flow rate adjusted for voided volume

OBJECTIVES

To investigate whether volume adjustment can be used to reduce the within-patient variability of the maximal urinary flow rate (Qmax) without affecting the variability between patients.

METHODS

We analyzed 2049 urinary flow curves of 208 men with lower urinary tract symptoms suggestive of bladder outlet obstruction and studied the relation between Qmax and voided volume (VV) in individual patients using multilevel regression analysis.

RESULTS

In agreement with most previous studies, we found a hyperbolic relation between the VV and Qmax. Although hyperbolic on average, the slope of the regression line relating the VV to Qmax differed substantially across individual patients. In some patients, Qmax even tended to be lower with an increased VV.

CONCLUSIONS

The reproducibility of Qmax is poor, in part because of its dependence on the VV. The current methods to adjust Qmax for VV, such as the Siroky nomogram, minimize between-patient dependency, whereas our findings emphasize the importance of within-patient variability. A common approach to adjust Qmax for VV, however, is not feasible, because the relation of Qmax to VV differs substantially across patients. The only valid, although impractical option, remains to record a large number of urinary flow curves for each patient.

The scaffold protein IB1/JIP-1 controls the activation of JNK in rat stressed urothelium

The c-Jun N-terminal kinase (JNK) is critical for cell survival, differentiation, apoptosis and tumorigenesis. This signalling pathway requires the presence of the scaffold protein Islet-Brain1/c-Jun N-terminal kinase interacting protein-1 (IB1/JIP-1). Immunolabeling and in situ hybridisation of bladder sections showed that IB1/JIP-1 is expressed in urothelial cells. The functional role of IB1/JIP-1 in the urothelium was therefore studied in vivo in a model of complete rat bladder outlet obstruction. This parietal stress, which is due to urine retention, reduced the content of IB1/JIP-1 in urothelial cells and consequently induced a drastic increase in JNK activity and AP-1 binding activity. Using a viral gene transfer approach, the stress-induced activation of JNK was prevented by overexpressing IB1/JIP-1. Conversely, the JNK activity was increased in urothelial cells where the IB1/JIP-1 content was experimentally reduced using an antisense RNA strategy. Furthermore, JNK activation was found to be increased in non-stressed urothelial cells of heterozygous mice carrying a selective disruption of the IB1/JIP-1 gene. These data established that mechanical stress in urothelial cells in vivo induces a robust JNK activation as a consequence of regulated expression of the scaffold protein IB1/JIP-1. This result highlights a critical role for that scaffold protein in the homeostasis of the urothelium and unravels a new potential target to regulate the JNK pathway in this tissue.

The effect of partial outlet obstruction on prostaglandin generation in the rabbit urinary bladder

Partial outlet obstruction of the urinary bladder has been demonstrated to induce specific dysfunctions in cellular and sub-cellular membrane structures within the bladder's smooth muscle and mucosal compartments. Recent studies have linked these membrane dysfunctions to alterations in phospholipid metabolism leading to mobilization of free arachidonic acid, the precursor for synthesis of prostaglandins (PG). The purpose of this study was to determine if partial outlet obstruction of the urinary bladder induces changes in the capacity of bladder smooth muscle and mucosa to generate PG. PG were isolated from control and partially obstructed urinary bladder smooth muscle and mucosa of male New Zealand White (NZW) rabbits. PG concentrations (PGE2, PGF2alpha and PGI2, as its stable metabolite 6-keto-PGF1alpha) were determined after 30 minute incubations using enzyme-linked immunoassay (ELISA) kits. In both control and obstructed rabbit urinary bladders, PG generation was significantly higher in isolated mucosa than muscle tissues. A significantly higher concentration of PGF2alpha, and 6-keto-PGF1alpha was measured in obstructed muscle tissue relative to controls. The concentration of 6-keto-PGF1alpha was also significantly higher than the concentrations measured for PGE2 and PGF2alpha in both control and obstructed smooth muscle samples. The generation of PGE2 was significantly higher in rabbit urinary bladder mucosa than either PGF2alpha or 6-keto-PGF1alpha in both control and obstructed samples. The capacity of obstructed mucosal tissue to generate 6-keto-PGF1alpha was significantly higher than control tissue, while no significant differences in PGE or PGF2alpha generation were noted. These data suggest obstruction of the urinary bladder induce specific elevations in PG in both smooth muscle and mucosal tissues.

Effect of partial outlet obstruction on 14C-adenine incorporation in the rabbit urinary bladder

Bladder outlet obstruction induces severe changes in urinary bladder function and metabolism. These changes are characterized by significant reductions in the ability of the in vitro whole bladder to generate pressure and to empty. Metabolically, partial outlet obstruction induces a shift from oxidative to anaerobic metabolism. The decreased oxidative metabolism is mediated in part by significant decreases in mitochondrial substrate metabolism, which in turn is correlated with decreased activity of 2 important mitochondrial enzymes: citrate synthase and malate dehydrogenase. The present study was designed to evaluate mitochondrial function by studying the incorporation of 14C-adenine into high-energy phosphates (ATP, AMP, and ADP). Mild partial outlet obstructions were created by surgically placing silk ligatures loosely around the bladder neck. The results of these studies demonstrate that after 60 min incubation in oxygenated medium containing glucose + 1uCi14C-adenine, 1) There was no significant differences in the total AMP, ADP, and ATP concentrations measured in bladders taken from controls, 7- and 14-day obstructed rabbits; 2) there was no effect of obstruction on either the concentration of 14C-AMP in the tissue or in the ratio of hot to cold AMP; and 3) there was a 50% decrease in the concentration of 14C-ADP and a 70% decrease in the concentration of 14C-ATP in the bladder smooth muscle obtained from obstructed tissue (from both 7- and 14-day obstructions) compared to concentration in the control bladder smooth muscle. These results confirm the previous finding that obstruction did not reduce the rate of incorporation of adenine to AMP within the obstructed bladder smooth muscle and extends these studies to identify a significant reduction in the synthesis of both ADP and ATP. These results support the hypothesis that partial outlet obstruction induce a major dysfunction in mitochondrial function, both in the ability to oxidize substrates and in the ability to generate ATP.

Compliance of the obstructed fetal rabbit bladder

We evaluated compliance in the developing bladder using a newly developed animal model of posterior urethral valves: partial infravesical obstruction in the fetal rabbit bladder. Partial bladder outlet obstruction was created in fetal rabbits at day 23 of a 31 to 32-day gestation period. An in vitro whole bladder preparation provided data on compliance and an isolated bladder strip preparation provided data on the mechanical properties of the bladder wall. In addition, the influence of calcium on both preparations was evaluated. Partial bladder outlet obstruction in the fetal rabbit resulted in a markedly larger bladder weight (246.4 +/- 22.3 mg, n = 14) than control bladders (90.2 +/- 5.7 mg, n = 13). Isolated smooth muscle strips from obstructed and normal bladders revealed identical stretch-stress patterns. In contrast, obstructed bladders had significantly increased compliance in the whole bladder preparation. Since the increase in compliance was not correlated to mechanical properties of the isolated bladder strips, it must therefore result from the pattern of mass increase of the whole bladder wall. During filling, both the control and obstructed bladders had the same slow, large amplitude spontaneous contractions. In addition, both had rapid contractions: those in the obstructed bladders had significantly lower frequency and higher amplitude than the ones in the control bladders. Removing the calcium from the organ bath eliminated the spontaneous contractions but did not change the baseline pressure or force values, indicating that the compliance of these fetal rabbit bladders is a function of the passive properties of the bladder wall. Three main patterns occur in cystometrograms of patients with posterior urethral valves: myogenic failure, hyperreflexic bladders, and low compliance bladders. Using our model of partial outlet obstruction in the fetal rabbit bladder, we could not imitate the group with low compliance. We therefore hypothesize that the different patterns of bladder dysfunction associated with posterior urethral valves are due to infravesical obstruction occurring with different severities or at different ages of gestation.

Correlation between the structure and function of the rabbit urinary bladder following partial outlet obstruction

PURPOSE

To understand the relationship between contractile and structural changes in the obstructed bladder, rabbit bladder was partially obstructed for up to 70 days and alterations in tension response to field stimulation and carbachol were compared with alterations in ultrastructure and innervation of detrusor smooth muscle (SM). The effect of partial outlet obstruction on the physiological responses to field stimulation (FS) (nerve mediated contraction) and carbachol (receptor mediated contraction) were correlated with the structure and innervation of the detrusor smooth muscle (SM) of the same animal during a 70 day period.

MATERIALS AND METHODS

28 rabbits were subjected to 1 to 70 days of mild partial outlet obstruction. Sham operated rabbits were euthanized at 7, 14, 28, and 70 days post-obstruction. At each time period, isolated strips of bladder body were mounted in individual baths and the contractile response to FS and carbachol determined. Three additional strips from each bladder were fixed for electron microscopy.

RESULTS

Bladder mass increased rapidly during the first 7 days after obstruction, was constant for the next 7 days, and then continued to increase gradually. Dysfunction of the contractile response to FS was noted as early as 3 days and progressively increased over the 70-day study period. The decrease in the response to FS increased at a significantly faster rate than the decrease in the contractile response to carbachol. In ultrastructure studies, at 3 and 7 days post-obstruction the majority of SM cells displayed the characteristics of hypertrophy. At 28 days some SM cells displayed loosely packed myofilaments and an irregular distribution of sarcoplasmic dense bodies. At 70 days swollen mitochondria were present in all cell types of the bladder wall. Evidence of axonal degeneration was first observed at 7 days post-obstruction and became more extensive thereafter. No evidence of mitotic figures, nerve growth cones or regenerating SM cells was observed.

CONCLUSIONS

Prolonged partial bladder outflow obstruction is accompanied by a progressive decrease in contractility of SM. The present study describes the structural damage that occurs in the bladder wall in response to partial outlet obstruction and correlates these observations with the contractile dysfunction with which it is associated. Furthermore, mitochondrial damage in vessels and fibroblasts is suggestive of bladder wall ischemia.

Effects of partial bladder outlet obstruction and its relief on types I and III collagen and detrusor contractility in the rat

Bladder outlet obstruction induces a rapid hypertrophy characterized by increased bladder mass and collagen deposition. An increase in collagen is likely to reduce the contractility and compliance of bladder wall. This study was undertaken to investigate the effects of partial bladder outlet obstruction and its relief on types I and III collagen, and the relationship between detrusor contractility and collagen types. A total of 40 female rats was used for experiment and divided into one control, one obstruction, and three recovery groups. The contractility to field stimulation was recorded; total collagen and collagen concentration were quantified. The localization of types I and III collagen and the expression of pro-alpha1(I) and alpha1(III) collagen mRNA were determined by immunohistochemical staining and Northern blot hybridization, respectively. Contractile response to field stimulation was reduced after obstruction and recovered following relief. The total amount of collagen increased after obstruction and decreased after relief; however, collagen concentration decreased after obstruction and increased following relief. Contractility correlated negatively with total collagen but positively with collagen concentration. The protein deposition of types I and III collagen was localized in lamina propria and muscle bundles in all groups. The expression of types I and III collagen gene was up regulated after obstruction, but down regulated after relief. Negative correlation between contractility and gene expressions of collagen types was significant. These data suggest that the change in localization and quantity of collagen types leads to morphologic changes of bladder and can have an impact on the contractility of detrusor. Neurourol. Urodynam. 19:29-42, 2000.

Fatty acid profiles in normal and obstructed rabbit bladder smooth muscle and mucosa

Partial bladder outlet obstruction results in progressive loss in contractile and specific cellular and subcellular membrane functions. There is evidence that ischemic activation of proteolytic and lipolytic enzymes play a major role in the etiology of bladder dysfunction secondary to partial outlet obstruction. The specific aims of the current study were to determine the fatty acid profiles in normal rabbit bladder smooth muscle and mucosa and to determine the effect of partial outlet obstruction on the distribution and content of free and total fatty acids. Fatty acids were isolated by extraction from obstructed and normal bladder smooth muscle and mucosal homogenates, and samples were analyzed by gas chromatography. All samples contained palmitic, stearic, oleic, linoleic, and arachidonic acids. A 100% increase in total fatty acid concentration was observed in the obstructed bladder muscle tissue relative to normal bladders, although the concentration of total arachidonic acid remained constant in the two groups. Significantly higher levels of free arachidonic acid were observed in the obstructed bladder muscle group compared to the normal group. No changes were observed in fatty acid concentrations or distributions in bladder mucosa. These data show that fatty acid composition is altered as a result of bladder obstruction and support the idea that obstruction increases the activity of lipase activity and/or decreases acyl transferase activity. Neurourol. Urodynam. 18:697-711, 1999.

Metabolic basis for contractile dysfunction following chronic partial bladder outlet obstruction in rabbits

Prior studies have shown that partial outlet obstruction of the rabbit bladder causes a progressive increase in bladder mass, a progressive decrease in the contractile response to different forms of stimulation, and a selective decrease in the activity of mitochondrial enzymes. In this investigation the contractile responses to field stimulation and bethanechol were directly correlated with the activity of citrate synthase as a function of both the duration of obstruction and the bladder mass. Partial bladder outlet obstruction was surgically induced in twenty New Zealand White rabbits. The bladders were then rapidly excised at 30, 40, 90, 105 or 150 days post obstruction. The contractile responses to field stimulation (32 Hz) and bethanechol (250 microM) were determined. The remainder of the bladders were frozen and used for citrate synthase activity determinations. The data were grouped for analysis both by the duration of obstruction and by the bladder mass. Chronic partial outlet obstruction caused a parallel decline in the activity of citrate synthase and in the response of the obstructed tissue to stimulation.

Mitochondrial and mitochondrial-related nuclear genetic function in rabbit urinary bladder following reversal of outlet obstruction

Partial outlet obstruction of the rabbit urinary bladder causes increased tissue hypertrophy and decreased contractility of that organ; we showed that, in an experimental rabbit model, both correlate closely with alterations in the status and expression of mitochondrial (mt), and mt-related nuclear, genetic parameters in bladder smooth muscle. Here we investigate the rate and overall level of recovery of mt and nuclear genetic function following reversal of outlet obstruction in the same animal model. Release from outlet obstruction at 28 days resulted in improvement in both level of hypertrophy and contractile function in all bladders studied. However, bladders fell into two groups based on whether relative copy mt genome number per cell was above or below that of unobstructed controls. Bladders with high mt DNA content adjusted organellar genome copy number toward normal post-reversal but did not properly adjust mt transcript levels; mt-related nuclear transcripts in these samples showed recovery. Bladders with low mt DNA content showed no adjustment of those levels toward normal post-reversal but did show some adjustment in other mt and nuclear genetic parameters. Thus, a limiting factor for return of normal bladder function following reversal of outlet obstruction may be recovery of normal mt genetic performance.

Neuronal nitric oxide synthase in the neural pathways of the urinary bladder

Nitric oxide (NO) is a unique biological messenger molecule. It serves, in part, as a neurotransmitter in the central and peripheral nervous systems. Neurons containing NO have been identified histochemically by the presence of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) reactivity or immunohistochemically by the antibody for neuronal NO synthase (n-NOS). Previous histochemical or pharmacological studies have raised the possibility that NO may play an important role in the neural pathways of the lower urinary tract. There is also considerable evidence to suggest that n-NOS is plastic and could be upregulated following certain lesions in the lower urinary tract. The present review summarises the distribution of n-NOS containing neurons innervating the urinary bladder and the changes of the enzyme expression in some experimentally induced pathological conditions.

Mitochondrial involvement in bladder function and dysfunction

Benign bladder pathology resulting from prostatic hypertrophy or other causes is a significant problem associated with ageing in humans. This condition is characterized by increased bladder mass, decreased urinary flow rate, decreased compliance, and these and other changes in bladder function often subject patients to increased risk of urinary tract infection. While the physiologic attributes of benign bladder pathology have been extensively described in humans and in various animal model systems, the biochemical and molecular genetic bases for that pathology have only recently been investigated in detail. Studies demonstrate that mitochondrial energy production and utilization are severely impaired in bladder smooth muscle during benign bladder disease, and to a large extent this realization has provided a rational basis for understanding the characteristic alterations in urinary flow and compliance in bladder tissue. Recent investigations targeting the detailed molecular basis for impaired mitochondrial function in the disease have shown that performance of the organellar genetic system, and to a large extent that of relevant portions of the nuclear genetic system as well, is severely aberrant in bladder tissue. In this article, we discuss the physiologic aspects of benign bladder disease, summarize biochemical evidence for the altered mitochondrial energy metabolism that appears to underlie bladder pathology, review the structure and function of the mitochondrial genetic system, and discuss molecular genetic studies of that system which have begun to provide a mechanistic explanation for the biochemical and physiological abnormalities that characterize the disease. We also discuss areas for further research which will be critically important in increasing our understanding of the detailed causes of benign bladder pathology.

Biochemical evaluation of obstructive bladder dysfunction in men secondary to BPH: a preliminary report

OBJECTIVES

In the rabbit, two of the major cellular alterations that mediate bladder dysfunction secondary to partial outlet obstruction are a decreased ability of the sarcoplasmic reticulum (SR) to store and release Ca2+, and mitochondrial dysfunction. The objective of the current study was to determine whether SR and mitochondrial dysfunctions are associated with symptomatic benign prostatic hyperplasia (BPH) in men.

METHODS

Bladder biopsies were obtained from men with symptomatic BPH and from age-matched men with no urologic dysfunction. Each biopsy was analyzed for the following enzyme activities: malate dehydrogenase and citrate synthase (mitochondrial markers) and the sarcoplasmic reticular enzyme Ca2+ -dependent adenosine triphosphatase (ATPase). These values were compared with the enzyme activities of control rabbit bladder smooth muscle and bladder smooth muscle obtained from rabbits subjected to 2 weeks of partial outlet obstruction.

RESULTS

The enzymatic activities of all three enzymes are significantly lower in human bladder smooth muscle than in rabbit bladder smooth muscle. The maximal activities of all three enzymes are significantly lower in human bladder samples obtained from men with diagnosed obstructive uropathy than in men of equal age with no urologic dysfunction.

CONCLUSIONS

These studies demonstrate that similar to the response of the rabbit to partial outlet obstruction, obstructive dysfunction secondary to BPH is characterized by mitochondrial and SR dysfunction.

Subcellular Distribution of Free Fatty Acids, Phospholipids, and Endogenous Lipase Activity of Rabbit Urinary Bladder Smooth Muscle and Mucosa

OBJECTIVES

The urinary bladder wall can be separated into two major compartments: the urothelium (mucosa) and the detrusor smooth muscle. Specific dysfunctions of both layers have been linked to ischemia, which may induce significant cellular and subcellular membrane damage via the activation of selective calcium dependent and independent hydrolytic enzymes. Preliminary to investigating changes in cell membrane composition induced by ischemia, we measured the free fatty acid (FFA) and phospholipid (PL) content of normal rabbit bladder muscle and mucosal cellular and subcellular membranes, and characterized the endogenous lipase activity.

METHODS

Rabbit bladders were excised and the muscle and mucosal layers separated; each layer was homogenized, then fractionated by differential centrifugation. Endogenous lipase activity of the homogenates, and FFA and PL concentrations of the homogenates and subcellular fractions were measured.

RESULTS

(1) The basal FFA concentration of the mucosal homogenates was 5 times that of the muscle homogenates. (2) The basal PL concentrations of the two tissues were similar. (3) Subcellular studies: FFA concentration was greatest in the mitochondrial fraction of both compartments. In the mucosa, PL concentration was significantly greater in the mitochondria and microsomes than in the other fractions; in the smooth muscle, the PL concentration was highest in the mitochondria. (4) The maximal endogenous lipase activity was 10 times higher in the mucosal homogenates than in the muscle homogenates.

CONCLUSIONS

These results are consistent with those of previous studies which indicate that the mucosa is metabolically more active than the resting smooth muscle, which may cause the mucosa to be significantly more sensitive than the muscle to hypoxic/ischemic damage.

Dog model for studying detrusor instability secondary to acutely induced variable bladder outlet obstruction

BACKGROUND

Involuntary detrusor contractions often cause irritative symptoms such as urgency and incontinence. A dog model for acutely induced variable bladder outlet resistance was developed to investigate the possible role of prostatic afferent nerve fibers in the development and maintenance of detrusor instability.

METHODS

Fifty-eight mongrel dogs (weight range 19.5-36.5 kg) were divided into five groups: group I (n = 11) had surgically induced bladder outlet obstruction. Group II (n = 14) had urinary obstruction and bilateral sectioning of the lowest branches of the pelvic plexus supplying the prostate. Group III (n = 10) had prostate denervation only. Groups IV (n = 10) and V (n = 13) were sham-operated and controls, respectively. In the obstructed groups (I and II), an artificial urinary sphincter (length 4.5-6.0 cm) was placed around the bladder neck and connected to a reservoir placed subcutaneously to allow postoperative adjustments of urinary resistance. All dogs were evaluated at baseline and postoperatively at 1, 3, and 6 months with uroflowmetry, postvoid residual urine volume, cystometry as well as serum creatinine, and urinalysis.

RESULTS

Occurrences of detrusor instability were not associated with prostatic denervation input. The mean peak flow rates decreased significantly in the obstructed groups at all follow-ups, but did not change significantly in the nonobstructed groups. Postoperatively, the mean maximum bladder capacity was significantly decreased for groups I and II only. However, a significant correlation between maximum bladder capacity and maximum detrusor pressure could not be detected at any time point in any of the groups. Mean postvoid residual urine volume varied considerably in all groups over time. Creation of a urinary model of infravesical obstruction was associated with considerable problems.

CONCLUSIONS

In our dog model of bladder outlet obstruction, prostatic sensory nerve fibers appear not to be involved in detrusor instability. Surgical induction of a constant model of bladder outlet obstruction was difficult even in a large animal. The observations from the present study raise questions about the validity of obstructive urinary animal models.

Influence of transient overdistension on bladder wall morphology and enzyme histochemistry

Bladder overdistension has been found to cause transitional morphological changes in innervation which correlate with changes in micturition and bladder contractility. We investigated the influence of overdistension on bladder wall morphology using histological and enzyme histochemical methods. Overdistension was induced in female rats for 3 h by forced diuresis and balloon obstruction of the bladder neck. Oedema was seen beneath the mucosa at 12 h, with hyperemia and haemorrhages. The urothelium was mostly intact, although enzymes leaked out of the epithelial cells. The changes were increased at 24 h. The urothelium also showed some disruptions and degenerative vacuolization. The oedema reached its maximum at 48 h, and large numbers of inflammatory cells were also seen. The urothelium was disruptured in many places and vacuolated, but the subendothelial capillaries remained normal. Damage to some muscle cells was seen. After 7 days the oedema had disappeared and the urothelium was continuous. Enlarged nuclei were seen as white spots in the epithelial cells. Numbers of inflammatory cells were similar to those in the controls. Overdistension causes damage primarily to the bladder urothelium, and to a lesser extent to the muscular layer. Urothelium integrity is destroyed for several days, which makes it possible for various substances to penetrate the bladder wall and allows for bacterial adherence. The damage however is, almost completely healed within one week.

Correlation of ischemia/reperfusion or partial outlet obstruction-induced spectrin proteolysis by calpain with contractile dysfunction in rabbit bladder

OBJECTIVES

In the rabbit, both experimental ischemia and partial outlet obstruction of the urinary bladder induce similar dysfunctions with regard to the contractile responses to both field (neuronal) stimulation and postsynaptic receptor stimulation. Circumstantial evidence indicates that the pathologic response to both conditions is related to two connected processes-tissue ischemia and reperfusion injury-that result in a marked increase in intracellular calcium ([Ca2+]i), followed by the activation of the Ca(2+)-dependent neutral protease calpain. Calpain activation results in the proteolysis of specific membrane proteins, including those of neuronal membranes (resulting in progressive denervation of the detrusor) and the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA), resulting in the previously reported decrease in SERCA. The current study is designed to generate direct support for the theory that both ischemia and partial outlet obstruction result in the activation of calpain.

METHODS

Separate sets of rabbits were subjected to 1 or 2 hours of ischemia, followed by reperfusion for different lengths of time, or partial outlet obstruction for different lengths of time. We determined the state of calpain activation by quantitating tissue proteolysis of alpha-spectrin by Western blot analysis. Correlative organ bath studies were conducted to observe the contractile responses of bladder strips to field stimulation and bethanechol administration.

RESULTS

(1) Sixty minutes of ischemia followed by 30 minutes of reperfusion resulted in (a) a reduction in the contractile responses to field stimulation and bethanechol (89% and 57%, respectively), and (b) a 72% decrease in native alpha-spectrin, with a concomitant 300% increase in its breakdown products (BDPs). Neither alpha-spectrin nor its BDPs had returned to control levels after 72 hours of reperfusion. (2) Twenty-four hours after the creation of a partial obstruction, alpha-spectrin BDP levels were increased 330%, then gradually fell to 130% of control levels by 14 days after obstruction. Concomitantly, the native alpha-spectrin level was decreased 74% 24 hours after obstruction and remained low through 7 days after obstruction. At 14 days after obstruction, the alpha-spectrin levels had recovered to 75% of control levels.

CONCLUSIONS

These findings suggest that Ca(2+)-dependent proteolysis of the preferred calpain substrate alpha-spectrin in urinary bladder tissues is increased significantly by both ischemia/reperfusion and partial outlet obstruction. Temporally, proteolysis precedes the reduced muscle function resulting from these pathologic conditions.

Ability of obstructed bladders to empty is dependent on method of stimulation

PURPOSE

To correlate pharmacologic changes that occur in the bladder after a partial outlet obstruction with the bladder's ability to perform work and empty.

METHODS

After 2 weeks of partial outlet obstruction, rabbit bladders were stimulated in vitro both isovolumetrically [field stimulation (FS)] and to empty (FS, bethanechol, and KCl).

RESULTS

The obstructed bladders were separated into two groups according to their ability to empty when stimulated with FS. Compensated bladders were those that could empty as much as controls. Decompensated bladders emptied significantly less than controls. With FS and bethanechol, the compensated obstructed bladders showed no difference from the control bladders in their ability to empty. In contrast, with KCl, the compensated bladders generated significantly less pressure, performed less work, and emptied less than controls. When the decompensated bladders were stimulated with all three types of stimulation, all parameters, including emptying ability, were significantly decreased.

CONCLUSIONS

The reduction in the response of compensated bladders to KCl stimulation suggested that the initial defects to the bladder after an outlet obstruction involved the interaction of smooth muscle proteins with calcium and ATP. In contrast, the response of decompensated bladders to all three forms of stimulation was equally reduced, suggesting that the degenerative processes were directly related to significant cellular damage to metabolic processes involved in energy synthesis, storage, and utilization.

Effect of ischemia and partial outflow obstruction on rat bladder function

We investigated the effects of ischemia induced by ligation of the bilateral internal iliac arteries following partial outlet obstruction on changes in detrusor function in rat. Rats were divided into three groups: sham-operated control rats, rats with partial outlet obstruction, and rats with obstruction+ischemia. Bladder function was studied by the in vitro organ bath technique 7 days after surgery. The weight of the bladder was significantly increased in both the obstruction and obstruction+ischemia groups. The obstruction+ischemia group exhibited a greater increase in weight. The passive length-tension relationship of detrusor muscle strips showed that tissue elasticity was decreased and the active length-tension relationship demonstrated that the peak response was observed at a shorter tissue length in the obstruction+ischemia group compared with the other two groups. There was no difference in the passive and active length-tension relationships between the control group and the obstruction group. The contractile response to various kinds of stimulation (field stimulation, bethanechol, ATP, and KCl) increased in the obstruction group and decreased in the obstruction+ischemia group. These findings suggest that partial outflow obstruction alone increased bladder contractility in response to stimuli. However, ischemia reduced the contractility and elasticity of the bladder wall.

Restoration of rat bladder function following release of short- and long-term partial outflow obstruction

Detrusor dysfunction does not recover in some patients with benign prostatic hyperplasia (BPH) even after prostate resection. 'We studied the functional restoration of the rat bladder after release of short- or long-term outflow obstruction. Bladder function was assessed by in vivo infusion cystometry and an in vitro organ bath technique. There were no significant differences in bladder weight and contractile strength induced by stimuli in detrusor muscle strips from obstructed rats and age-matched control rats. After short-term obstruction the whole bladder pressure generated in vitro by field stimulation, bethanechol, ATP, and KCl completely recovered to control levels. In contrast, after long-term obstruction, the whole bladder pressure in response to field stimulation remained significantly lower than in controls. Infusion cystometry variables, including the pressure at which micturition was induced, maximal voiding pressure, capacity, and residual urine volume, were similar between controls and rats subjected to short-term obstruction. However, the maximal voiding pressure after long-term obstruction was significantly less than that of controls.

Influence of hormone treatment on prostate growth and micturition characteristics of the rat

The influence of dihydrotestosterone propionate (DHT) and estradiol (E) on prostate growth and micturition was evaluated. Complete studies were carried out on 49 Sprague-Dawley rats over a 14-day period. Rats were divided into three groups: (1) controls, (2) DHT, and (3) DHT + E. All groups were injected daily with 0.1 ml of sesame oil, together with 1.25 mg/kg of DHT for group 2 and 1.25 DHT + 0.125 mg/kg E for group 3. Physiological measurements of micturition were done weekly by subcutaneously administering a fluid loading dose consisting of 10 mg/kg furosemide + 5 ml saline. Parameters of micturition frequency, volume, and prostate weight were calculated. Prostate weight values for controls were 0.89 +/- 0.06 g while those treated with DHT increased significantly to 1.26 +/- 0.10 g (P < 0.05) and those treated with DHT + E also increased significantly to 1.24 +/- 0.09 g (P < 0.05). There was no significant difference in prostate weight between the DHT and DHT + E groups. Analysis of micturition data shows that the mean volume voided per micturition decreases in both the DHT and DHT + E treated rats. At between 7 and 14 days of DHT and DHT + E treatment, rats micturated at significantly reduced mean volumes. The lowest mean volume per micturition was detected on the 14th day of DHT treatment, showing a significant reduction from control values of 3.05 +/- 0.27 to 1.68 +/- 0.05 ml. The corresponding value of the mean micturated volume in the DHT + E groups was 1.86 +/- 0.31 ml. Control values for frequency of micturition was 3.25 +/- 0.52/hr, while for rats treated with DHT it was 3.62 +/- 0.38/hr and for DHT + E it was 4.0 +/- 0.54/hr. Evidence is provided to demonstrate that 14 day DHT, and particularly DHT + E, stimulation produces significant alterations in prostate weight and micturition characteristics of unanesthetized rats. On the basis of these observations it is proposed that the hormonally enlarged prostate promotes stimuli to trigger the spinal micturition reflex, thereby producing increased frequency of micturition.

Smooth-muscle physiology

In the last several years, significant advances have been made in the understanding of bladder smooth muscle physiology. This article provides a summary for the clinician of current knowledge about the detrusor smooth muscle cell structure, function, and the relationship of structure to function in terms of bladder storage and physical properties such as compliance. The integration of this basic science knowledge into clinical practice is illustrated in discussion of two common disorders: detrusor instability, and outflow obstruction.