Effect of partial outlet obstruction on choline acetyltransferase activity in the rat and rabbit

Benefits and limitations of animal models in partial bladder outlet obstruction for translational research

The functions of the lower urinary tract have been investigated for more than a century. Lower urinary tract symptoms, such as incomplete bladder emptying, weak urine stream, daytime urinary frequency, urgency, urge incontinence and nocturia after partial bladder outlet obstruction, is a frequent cause of benign prostatic hyperplasia in aging men. However, the pathophysiological mechanisms have not been fully elucidated. The use of animal models is absolutely imperative for understanding the pathophysiological processes involved in bladder dysfunction. Surgical induction has been used to study lower urinary tract functions of numerous animal species, such as pig, dog, rabbit, guinea pig, rat and mouse, of both sexes. Several morphological and functional modifications under partial bladder outlet obstruction have not only been observed in the bladder, but also in the central nervous system. Understanding the changes of the lower urinary tract functions induced by partial bladder outlet obstruction would also contribute to appropriate drug development for treating these pathophysiological conditions. In the present review, we discuss techniques for creating partial bladder outlet obstruction, the characteristics of several species, as well as issues of each model, and their translational value.

Comparative biochemical responses and antioxidant activities of the rabbit urinary bladder to whole grapes versus resveratrol

The objective of this study is to compare the antioxidant activity of a whole-grape suspension with the antioxidant activity or pure resveratrol on the effect of hydrogen peroxide (H2O2) on malondialdehyde (MDA) generation, choline acetyltransferase (ChAT) activity, calcium ATPase activity, and sarcoendoplasmic reticular ATPase (SERCA) of the male rabbit urinary bladder. MDA was used as a model for the effect of H2O2 on lipid peroxidation. ChAT, SERCA, and calcium ATPase were evaluated based on their importance in urinary bladder physiology and pathology. Four male rabbit bladders were used. Each bladder was separated into muscle and mucosa, frozen under liquid nitrogen and stored at -80 °C for biochemical evaluation. The effect of H2O2 on the enzymes listed above was determined in the presence and absence of either resveratrol or a whole-grape suspension. (1) Resveratrol was significantly more effective than the grape suspension at protecting the bladder muscle and mucosa against peroxidation as quantitated by MDA formation. (2) The grape suspension was significantly more effective at protecting ChAT activity against oxidative stress of the muscle than resveratrol. (3) Neither the grape suspension nor resveratrol were particularly effective at protecting the bladder muscle or mucosa calcium ATPase or SERCA against oxidative stress. (4) ChAT was significantly more sensitive to oxidative stress than either calcium ATPase or SERCA. These data support the idea that the grape suspension protects the mitochondria and nerve terminals to a significantly greater degree than resveratrol which suggests that the activities of the grape suspension are due to the combination of active components found in the grape suspension and not just resveratrol alone.

Bladder outlet obstruction causes up-regulation of nicotinic acetylcholine receptors in bladder-projecting pelvic ganglion neurons

Pelvic ganglion (PG) neurons relay sympathetic and parasympathetic signals to the lower urinary tract, comprising the urinary bladder and bladder outlet, and are thus essential for both storage and voiding reflexes. Autonomic transmission is mediated by activation of the nicotinic acetylcholine receptor (nAChR) in PG neurons. Previously, bladder outlet obstruction (BOO), secondary to benign prostatic hyperplasia, was found to increase soma sizes of bladder-projecting PG neurons. To date, however, it remains unknown whether these morphological changes are accompanied by functional plasticity in PG neurons. In the present study, we investigated whether BOO alters acetylcholine receptor (nAChR) transcript expression and current density in bladder PG neurons. Partial ligation of the rat urethra for six weeks induced detrusor overactivity (DO), as observed during cystometrical measurement. In rats exhibiting DO, membrane capacitance of parasympathetic bladder PG neurons was selectively increased. Real-time PCR analysis revealed that BOO enhanced the expression of the transcripts encoding the nAChR α3 and β4 subunits in PG neurons. Notably, BOO significantly increased ACh-evoked current density in parasympathetic bladder PG neurons, whereas no changes were observed in sympathetic bladder and parasympathetic penile PG neurons. In addition, other ligand-gated ionic currents were immune to BOO in bladder PG neurons. Taken together, these data suggest that BOO causes upregulation of nAChR in parasympathetic bladder PG neurons, which in turn may potentiate ganglionic transmission and contribute to the development of DO.

Estrogen administration attenuates bladder outlet obstruction induced oxidative stress in the female rabbit

AIMS

Estrogen administration to female rabbits induces a functional hypertrophy of the bladder. The aim of this study was to investigate whether supplementation of estrogen in the female rabbit with partial bladder outlet obstruction (PBOO) would affect the severity of bladder dysfunction.

METHODS

We surgically created PBOO in female New Zealand White rabbits. Group 1 included sham operated rabbits which served as controls. Group 2 received PBOO without estrogen treatment. Group 3 received estrogen treatment after PBOO. Group 4 received estrogen pretreatment before PBOO. The bladders were then removed for contractile, biochemical, and protein expression studies. There were four rabbits per group.

RESULTS

(1) PBOO resulted in significant decreases in the contractile responses to all forms of stimulation (field stimulation [FS], carbachol, KCl, ATP). Both pretreatment and post-treatment with estrogen resulted in significantly increased contractile responses to all forms of stimulation, although the responses were still lower than control. (2) PBOO resulted in a significant decrease in the activity of choline acetyltransferase (ChAT). Both pretreatment and post-treatment with estrogen resulted in significant increases in ChAT activity back toward control levels. (3) PBOO resulted in significant increases in both protein oxidation and nitration; both pretreatment and post-treatment with estrogen significantly reduced oxidation and nitration toward control levels.

CONCLUSIONS

Estrogen pretreatment and post-treatment in the female rabbit ameliorated contractile and biochemical dysfunctions associated with PBOO. This improvement is likely due to reduced oxidative stress. As expected, pretreatment was generally more effective than post-treatment.

Effects ofl-arginine andl-NAME on chronic partial bladder outlet obstruction in rabbit

Nitric oxide (NO) is synthesized from l-arginine by nitric oxide synthase (NOS). NOS can be inhibited by NG-nitro-l-arginine methyl ester (l-NAME) and stimulated by supplementing the diet with l-arginine. The aim of this study was to investigate the influence of NOS activity on the response of rabbits to chronic partial bladder outlet obstruction (PBOO). Surgical PBOOs (2 and 8 wk) were performed on male New Zealand White rabbits. Before obstruction, one-third of the animals were premedicated for 7 days with l-NAME and another third with l-arginine. The results are summarized as follows. First, bladder weight after 8-wk PBOO was significantly lower in animals treated with l-arginine compared with both untreated and rabbits treated with l-NAME. Second, contractile function decreased progressively with PBOO duration. However, after 8 wk of PBOO, the l-arginine group had significantly greater contractile function compared with the no-treatment group, and the l-NAME group had significantly lower contractile function compared with the no-treatment group. Third, at 8 wk following PBOO, the level of protein oxidation and nitration was lowest for the l-arginine group and highest in the l-NAME group. These studies clearly demonstrated that increasing blood flow by stimulating NOS significantly protected the bladder from PBOO dysfunctions, whereas inhibiting blood flow by l-NAME enhanced the dysfunctions mediated by PBOO.

Effect of short-term outlet obstruction on rat bladder nerve density and contractility

1 The present study was designed to investigate the relationship between innervation density and contractile responses to field stimulation and exogenous agonists at early time points after induction of bladder outlet obstruction (BOO) in rats. 2 When compared with sham-operated animals, 1, 3 and 7 days of BOO were associated with a 75%, 80% and 90% increase of bladder weight. Field stimulation caused a frequency-dependent increase in force of contraction. The force of contraction was reduced at each frequency in BOO rats with the greatest decrease after 1 day and a gradual but incomplete recovery thereafter. In contrast, contractile responses to ATP, carbachol and KCl were markedly reduced after 1 day of BOO and fully recovered after 7 days. The neurofilament staining was not altered by 1 day of BOO, but gradually decreased with increasing duration of BOO reaching the lowest levels after 7 days. 3 We conclude that impaired cellular contractility seems to underlie the early reductions of field stimulation-induced contraction, possibly reflecting surgical trauma of the tissue. However, at later time points a reduced nerve density, possibly reflecting a partial denervation, appears to be the main reason for impaired contractile response to field stimulation.

Effect of castration on male rabbit lower urinary tract tissue enzymes

OBJECTIVES

The influence of testosterone on the prostate and corpus cavernosum have been studied extensively. However, the influence of testosterone on the lower urinary tract (bladder and urethra) have not been investigated to any great extent. The aim of this study was to determine whether androgen deprivation alters lower urinary tract metabolism.

METHODS

A total of 16 rabbits were divided into four groups of four rabbits each. Each rabbit in groups 1-3 underwent surgical bilateral castration for duration of 1, 2 , and 4 weeks, and group 4 underwent sham operations. Sections of bladder body and base wall and mucosa, urethra and corpora were isolated, frozen, and stored under liquid nitrogen. The activities of citrate synthase-thapsigargin sensitive Ca(2+) ATPase (Sarco/Endoplasmic Reticulum Ca(2+ )ATPase [SERCA]), and choline acetyl-transferase were examined as markers for mitochondrial function, sarcoplasmic reticular calcium storage and release, and cholinergic nerve function, respectively.

RESULTS

The activity of SR function indicator, Ca(2+) ATPase was significantly higher in the control corpora than in the control bladder or urethra. Castration resulted in decreased activity in the mitochondria specific enzyme, citrate synthase, the activity of which was greatest in the urethra and lowest in the corpora. Cholinergic nerve density indicator, choline acetyl-transferase activity was greatest in the bladder body and lowest in the urethra.

CONCLUSIONS

Our data indicate that (1) significant differences exist in the activities of all three enzymes in the various organs associated with the lower urinary tract; and (2) that castration results in significant alterations in the activities of all three enzymes in the bladder body, base, urethra, and corpora.

Alterations in purinergic and cholinergic components of contractile responses of isolated detrusor contraction in a rat model of partial bladder outlet obstruction

OBJECTIVE

To study the effect of 3 weeks of partial bladder outlet obstruction (BOO), compared to a sham operation, on the cholinergic and purinergic components of detrusor contractile responses to agonists and to electrical field stimulation (EFS); the expression of P2X receptor subtypes was also examined.

MATERIALS AND METHODS

Partial BOO was induced in female Sprague-Dawley rats by surgically applying a jeweller's silver 'jump' ring around the urethra, such that the urethra was constricted but not closed. Sham-operated female rats underwent an identical procedure without placement of a ring.

RESULTS

After 3 weeks of partial BOO the rat bladders became significantly hypertrophied, doubling in weight. Spontaneous activity was markedly increased, but the contractile response to a single bolus of KCl (120 mM) was unaltered. The neurogenic-induced contractile responses of strips of detrusor from obstructed bladders were significantly greater than those from sham-operated bladders, and the responses of strips of detrusor from obstructed bladders to EFS showed a significantly greater atropine-sensitive component than sham-operated detrusor. However, the response of detrusor strips to EFS that was susceptible to desensitization by alpha,beta-methylene ATP was not significantly changed in obstructed bladders. The sensitivity of the strips from obstructed bladders to carbachol, ATP and beta,gamma-methylene ATP was less than in sham-operated detrusor. Immunohistochemical studies showed no difference in the P2X receptor subtypes expressed on detrusor smooth muscle from obstructed and sham-operated rats.

CONCLUSION

In the rat, after moderate bladder hypertrophy, the atropine-sensitive component was significantly up-regulated, but the ATP-sensitive component was marginally reduced, although not significantly. These results suggest that up-regulation of the P2X component of bladder contraction seen in humans with bladder instability, and in other species models of BOO, is not mirrored in the rat, or occurs later in the pathological process of bladder hypertrophy.

Early treatment of benign prostatic hyperplasia: implications for reducing the risk of permanent bladder damage

A significant change has occurred in the management of symptomatic benign prostatic hyperplasia (BPH) since effective pharmacological treatment became available and led to a significant decrease in the number of surgical procedures in many Western countries. The hypothesis of a causative role of benign prostatic enlargement and bladder outflow obstruction (BOO) in lower urinary tract symptoms (LUTS) was based on the association between prostate growth and symptoms of prostatism in elderly men and on the dramatic reduction of LUTS upon relief of obstruction. Careful investigation into the epidemiology of LUTS and BPH failed to confirm such an association and opened new perspectives in the pathophysiology of lower urinary tract dysfunction and symptoms. The observation that LUTS were equally distributed in male and female cohorts, when matched for age, moved attention away from the prostate and towards the urinary bladder and its aging-related disorders. When BPH surgery was developed, the management of the disease was aimed at preventing death from chronic renal failure, but the picture has changed and modern medical treatment is now aimed at improving the patient's quality of life. The increasing size of elderly populations in the Western world and the consequent financial constraints of national healthcare systems have raised the question of when pharmacological treatment of symptomatic BPH should be initiated. Retrospective and prospective analysis of various BPH populations and clinical studies has clearly defined the capacity of pharmacological treatment to reduce the incidence of complications of BPH, such as acute urinary retention and the need for surgery, but the cost/benefit ratio is unclear. Notwithstanding the limitations inherent in the experimental models, there is evidence from various animal models, investigating the pathophysiology of the urinary bladder in the presence of outflow obstruction, to indicate that a cause and effect relationship between BOO and bladder decompensation has been established and to support the hypothesis that permanent bladder damage may occur when the obstruction is not relieved early enough. Preliminary experimental evidence also suggests that alpha(1)-adrenoceptor antagonists may have a role in reducing the damaging effects of BOO on the urinary bladder. At present, there is no evidence to support the need for early pharmacological treatment of symptomatic BPH with no BOO beyond the obvious target of improving the patient's quality of life. The evidence for early treatment of BOO and the need to preserve bladder function is clear. Further experimental and clinical research is required to identify markers of early bladder damage and decompensation which can be used to select patients for early pharmacological treatment of BPH.

The decompensated detrusor III: impact of bladder outlet obstruction on sarcoplasmic endoplasmic reticulum protein and gene expression

PURPOSE

Regulation of calcium ion homeostasis has a significant role in smooth muscle contractility. The sarcoplasmic endoplasmic reticulum, calcium, magnesium, adenosine triphosphatase (SERCA) is a regulatory ion pump that may have a role in the functional outcome after outlet obstruction. We investigate what correlation if any existed between SERCA protein and gene expression, and the contractile properties in the same bladder.

MATERIALS AND METHODS

Standardized partial bladder outlet obstructions were created in adult New Zealand white rabbits, which were divided into control, sham operated and obstructed groups. Muscle strip studies subcategorized the obstructed group into compensated (force greater than 50% of control) and decompensated (force less than 50% of control). Microsomal membrane and total RNA fractions were prepared from the same bladder tissue. Membrane proteins were used for Western blot analysis using a SERCA specific monoclonal antibody, and total RNA was assessed with Northern blot analysis.

RESULTS

The relative intensities of signals for the Western and Northern blots demonstrated a strong correlation between protein and gene expression. Furthermore there was a strong association between the loss of SERCA messenger RNA and protein expression and loss of bladder function.

CONCLUSIONS

Bladder contractility after outlet obstruction is influenced in part by smooth muscle cell ability to maintain calcium homeostasis via SERCA. The loss of SERCA protein expression is mediated by down-regulation in gene expression in the same bladder. These data suggest that smooth muscle ion pump gene expression is in part mechanically (pressure work) regulated.

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.

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.

Effect of partial outlet obstruction on the myogenic response to field stimulation

1. Experimental studies of outlet obstruction have been performed on rats, rabbits, guinea pigs, cats, dogs and pigs. There is evidence that partial outlet obstruction can alter the membrane properties of the bladder smooth muscle and result in progressive denervation. The current studies were designed to evaluate the effects of moderate partial outlet obstruction on the response of isolated strips of rabbit bladder smooth muscle to field stimulation in the absence and presence of tetrodotoxin (TTX). 2. The results are as follows: In the absence of TTX, partial outlet obstruction resulted in a significant reduction in the neurogenic response at all frequencies. In the presence of 1 microM TTX, which caused maximal inhibition of the release of neurotransmitters, partial outlet obstruction caused a significant increase in the myogenic response to field stimulation. 3. These studies clearly demonstrate that partial outlet obstruction results both in a significant decrease in the neurogenic response of the obstructed bladder to field stimulation and in a significant increase in the myogenic component.

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.

Bladder function in experimental outlet obstruction: pharmacologic responses to alterations in innervation, energetics, calcium mobilization, and genetics

The two functions of the urinary bladder is to store urine at low intravesical pressures, and to periodically expel the urine through a coordinated contraction of the bladder and relaxation of the urethra. To a large extent, urinary bladder function depends upon the underlying structure of the organ as a whole, particularly on the inter-relationships among the smooth muscle, connective tissue, and neuronal elements. An alteration in the ratio of connective tissue to smooth muscle, for example, can significantly alter compliance and functional capacity, structurally impairing the bladder's ability to empty efficiently and fully. Thus, a change in structural compartmentation can affect bladder function independent of autonomic receptor density, response to receptor stimulation, and the contractile capabilities of the smooth muscle elements. Similarly, a selective alteration in either the afferent or efferent innervation of the bladder or urethra can induce significant alterations in the structural interrelationships between smooth muscle and connective elements. In addition, the bladder responds rapidly to alterations in urine volume and urethral resistance with marked changes in bladder and urethral structure and function, and these changes are under the controls of specific genes that are known to control cellular growth, hypertrophy, and hyperplasia. A knowledge of the mechanisms that control the response to specific forms of stress may lead to novel therapies for specific disease states.

Effect of partial outlet obstruction on contractility: comparison between severe and mild obstruction

Detrusor dysfunction is one of the most common problems in patients with outflow obstruction secondary to benign prostatic hyperplasia. These patients complain of various symptoms, including urinary frequency, urge incontinence, difficulty in voiding, and retention. The severity of the symptoms is dependent on the stage of disease and/or severity of the obstruction. We compared the changes in the rat detrusor function following both mild and severe models of partial outlet obstruction in the rat. Outflow obstructions were created by ligation of the urethra over which a catheter was placed. The size of the catheter determined whether the severity of obstruction was mild or severe (1.70 mm for mild obstruction and 1.09 mm for severe obstruction). Changes in the bladder weight, length-tension relationships, and the contractile response to field stimulation, pharmacologic agonists, and KCl were studied in bladders isolated from 1 and 2 week obstructed rats. Bladder weights of all obstructed rats increased significantly. The weight of the severe obstructed rats were significantly greater than rats subjected to mild obstruction. In general, passive length-tension curves of obstructed rats were shifted to right. The magnitude of the active tension induced by high KCl was higher in the mild obstruction and lower in the severe obstruction. The maximum response to KCl of mild obstruction was generated at greater lengths than for the other groups. In general, the contractile responses of the mild obstructed bladder body to field stimulation, bethanechol, KCl, and ATP, and of the bladder base to field stimulation, KCl, and methoxamine, were significantly increased when compared to the responses of the control bladder body and base. However in the severe obstructed bladder, the responses to field stimulation, KCl, ATP, and methoxamine were significantly reduced from the responses of the control strips; the response to bethanechol was similar for control and the severe obstructed groups. In conclusion, the severity of outlet obstruction significantly altered the contractile response of the bladder. Mild obstruction induced a mild increase in bladder mass, which was associated with significant increases to all forms of stimulation. Severe outflow obstruction induced a substantial increase in bladder mass and a significantly greater reduction in the response to field stimulation than the response to bethanechol (which was unchanged).