The effect of ovariectomy on the contractile response of the rat isolated detrusor muscle and urethra

Gap junction expression and the effects of gap junction inhibitors in overactive bladder models: does ovariectomy have a role?

PURPOSE

In this study, gap junction expression and the effects of estrogen deficiency and gap junction inhibitors were investigated in overactive bladder models which were created by bladder outlet obstruction.

METHODS

In our study, we created four groups as control, ovariectomy, bladder outlet obstruction (BOO), and ovariectomy + BOO. We investigated the effects of oxybutynin and 18-alpha glycyrrhetinic acid (18-α-GA) which is a gap junction blocker on isolated detrusor strips. Western blot method was used to measure the level of connexin-43 in detrusor.

RESULTS

Bladder weights were significantly increased in the BOO and ovariectomy + BOO groups (p < 0.05). There was no statistically significant difference in the maximal contraction responses to carbachol between ovariectomy and control groups. In BOO and ovariectomy + BOO groups, contractile responses were significantly prominent with higher doses of carbachol. Oxybutynin-induced relaxant responses of BOO and ovariectomy + BOO groups were significantly higher than control group (p < 0.05). The relaxation effect of 18-a-GA was more effective in the obstruction groups. Among those two groups, the relaxation observed in BOO group was higher than ovariectomy + BOO group in higher doses of 18-a-GA. Connexin-43 expression was increased in BOO group compared with the control group (p = 0.006). Ovariectomy did not change connexin-43 expression alone; however, when combined with BOO, connexin-43 expression decreased significantly (p = 0.023).

CONCLUSIONS

Ovariectomy had no effect on the gap junctions in the bladder and bladder overactivity alone. Therefore, obstruction is the main factor that increases the amount of gap junctions, and gap junction blockers are thus more effective in obstruction. However, ovariectomy was shown to decrease the expression of gap junctions and relaxation effect of gap junction blockers, when combined with BOO.

[Role of estrogens in lower urinary tract physiology and physiopathology]

GOAL

The aim was to review the literature on estrogens and lower urinary tract.

MATERIAL

A review of literature through the PubMed library until December 31, 2012 was carried out using the following keywords: lower urinary tract, bladder, urethra, nervous central system, innervation, female, women, estrogen, estradiol, urogenital atrophy, urinary incontinence, overactive bladder, urinary tract infection.

RESULTS

On the bladder, estrogens are involved in the trophicity, vascularisation, alpha-adrenergic, cholinergic and muscarinic receptor density, detrusor contractility and inflammation. On the urethra, they impact vascularisation, contractility, urethral pulse and tone, anatomical and functional length. On the neurological control, they act on capsaicin-sensitive afferent fibres, neurological regeneration, nerve growth factor expression and viscerovisceral sensitisation.

CONCLUSION

Estrogens play a major role on the lower urinary tract physiology and physiopathology both on the urethra and the bladder.

Dietary phytoestrogens maintain contractile responses to carbachol with age in the female rat isolated bladder

AIMS

Development of urinary incontinence, for many women, occurs following menopause. Dietary phytoestrogens consumed over the long term may affect the contractile function and maintenance of the urinary bladder in post menopausal women. This study examined the muscarinic receptor mediated contractile responses in the rat isolated bladder in response to ovariectomy and long term dietary phytoestrogen consumption.

MAIN METHODS

Ovariectomised or sham-operated female Wistar rats (8 weeks) were fed either normal rat chow (soy, phytoestrogens) or a non-soy (phytoestrogen free) diet. Bladders were dissected from rats at 12, 24 and 52 weeks of age and placed in 25 ml organ baths filled with McEwans solution.

KEY FINDINGS

The contractile response to carbachol, in 12 week old female rats did not change as a result of dietary phytoestrogens or ovariectomy (P>0.05). At 24 weeks of age, detrusor muscle strip responses to carbachol from non-soy fed ovariectomised rats were attenuated (P<0.05). At 52 weeks, bladder detrusor strip responses to carbachol were reduced in all treatment groups with the exception of the soy-fed sham operated rats.

SIGNIFICANCE

These results suggest an age-related reduction in the contractile response of the detrusor to the muscarinic receptor agonist carbachol, which may be prevented by long term dietary phytoestrogen intake.

Dietary soy isoflavone replacement improves detrusor overactivity of ovariectomized rats with altered connexin-43 expression in the urinary bladder

To evaluate the effects of dietary soy isoflavone on detrusor overactivity (DO) in ovariectomized (Ovx) rats and the association between these effects and expression of the gap junction protein, connexin-43, in the urinary bladder, and to discuss the usefulness of soy isoflavones for overactive bladder (OAB).

MATERIALS AND METHODS

In all, 24 (8-week-old) virgin female Sprague-Dawley rats were divided equally into four groups: sham operation with control diet (with no dietary soy isoflavones; Sham-CD), bilateral Ovx with CD (Ovx-CD), sham operation with soy isoflavone diet (Sham-ID), bilateral Ovx with soy ID (Ovx-ID). Cystometry was performed after the 4-week CD or ID in each group while awake. Quantitative reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemical and Western blot analyses were also performed to examine the expression of connexin-43 in each group.

RESULTS

In Ovx-CD rats, there were some significant changes in cystometry variables, including shortening of the intercontraction interval and an increased number of non-voiding contractions compared with Sham-CD rats (P < 0.05). These changes were significantly improved by 4-week soy isoflavone administration (Ovx-ID; P < 0.05). Quantitative RT-PCR, immunohistochemical and Western blot analyses showed that the expression level of connexin-43 mRNA and protein was significantly greater in the urinary bladder of Ovx-CD rats compared with Sham-CD rats. Soy isoflavone administration significantly reduced this increased expression (Ovx-ID).

CONCLUSIONS

Soy isoflavone replacement improved DO with alteration of the connexin-43 expression pattern in the urinary bladder of Ovx rats. Routine consumption of diet soy isoflavones may be a useful treatment to prevent and improve OAB.

Functional and anatomical effects of hormonally induced experimental prostate growth: a urodynamic model of benign prostatic hyperplasia (BPH) in the beagle

BACKGROUND

Benign prostatic hypertrophy (BPH) produces a variety of changes in the urodynamic pattern of micturition and is usually associated with high detrusor voiding pressure and poor urine flow-rate. In most previous experimental models, designed to simulate this condition, some degree of obstruction is immediately imposed by the technique employed to produce urethral occlusion. Consequently these models cannot reproduce the gradual onset of obstruction. In the present study a canine prostatic enlargement model, using 5alpha-dihydrotestosterone (DHT) + 17beta-estradiol (E) was adapted in order to produce a more gradual onset of partial obstruction and impaired voiding.

MATERIALS AND METHODS

Hormonally induced prostatic enlargement was produced using seven beagles, given DHT 75 mg/day together with E 0.75 mg/day for 28 days via an implantable pump. The functional effects of DHT + E treatment on micturition pressure/flow were measured in the conscious animal. Identical measurements were also made using a separate older group of five beagles with symptoms of BPH. In addition seven beagles similarly instrumented were used as controls.

RESULTS

Pressure/flow studies show that DHT + E produced obstructive micturition, characterized by a significantly increased micturition detrusor pressure, from 33.3 +/- 10.5 to 50.8 +/- 10.7 cmH(2)O and significantly decreased low urine flow-rate from 8.6 +/- 2.1 to 6.9 +/- 0.9 ml/sec. Associated with the obstructive micturition, this treatment increased wet prostate weight from 11.9 +/- 2.5 to 31.6 +/- 10.0 g. Prostate volume of the BPH beagles was 29.3 +/- 8.9 g. Morphologic studies show that DHT + E produced epithelial hyperplasia extending focally into the lumen.

CONCLUSIONS

Hormonally induced prostate growth produced bladder obstruction, in terms of pressure/flow characteristics, that are analogous to BPH. It is suggested that this type of hormonal treatment can be used to create a model for the study of the effects of controlled increased in prostate growth and the development of BPH on micturition.

Urodynamic effects of estradiol (E2) in ovariectomized (ovx) rats

Whether estrogens have a beneficial effect in the urinary bladder to prevent or to delay occurrence of urinary bladder incontinence is an open question. Good animal models are missing. Therefore, in ovariectomized (ovx) rats we studied the effects of estradiol (E2) administered with food for 3 mo on urodynamic properties of the urinary bladder and the urethra. A biluminal catheter with one outlet in the bladder and another in the urethra in juxtaposition to the external sphincter was inserted in isoflurane anaesthetized animals. Within 2 x 30 s (1 min apart) 0.5 mL Ringer's solution was infused into the bladder and the inner vesicular and urethral pressure were recorded. In comparison to ovx estradiol-treated rats, ovx animals had significantly (p < 0.05) lower vesicular and urethral pressure. In the sham-treated ovx animals vesicular and urethral pressures were unstable and appeared uncoordinated, whereas estrogens increased vesicular and urethral pressure in a coordinated way, such that in these animals leaked volume was significantly lower than in the sham-treated ovx animals. By means of quantitative RT-PCR we demonstrate that the upper and lower part of the bladder and the urethra express estrogen receptor of the alpha- and beta-subtype (ER alpha and beta) and nerve growth factor, which is associated with painful sensations in inflamed urinary bladders. E2 downregulated both ERs in the bladder but not in the urethra, while NGF gene expression was downregulated in the urethra but unaffected by E2 in the bladder. It is concluded that estrogen deprivation causes uncoordinated function of the detrusor and sphincter muscles and that this effect can be prevented by estradiol.

The effect of ovariectomy and estradiol replacement on collagen and elastic fibers in the bladder of rats

The authors quantified the collagen and elastic fibers in the bladder wall of ovariectomized rats with and without estradiol replacement. This study was conducted on 60 3-month-old Wistar rats. Group 1 remained intact; group 2 underwent bilateral ovariectomy and were sacrificed after 30 days; group 3 were sham operated and sacrificed after 30 days; group 4 had a bilateral ovariectomy and after 30 days were started on subcutaneous injections of 17beta-estradiol (10 microg/kg body weight) for 90 days; group 5 were sham operated and after 30 days were on started subcutaneous sesame oil replacement (0.2 ml/day) for 90 days; group 6 had a bilateral ovariectomy and after 30 days were started on subcutaneous sesame oil replacement (0.2 ml/day) for 90 days. Sirius red and Weigert's resorcin-fuchsin were used to stain collagen and elastic fibers on paraffin-embedded rat bladder sections. The M-42 grid system was used to quantitatively analyze the fibers. Ovariectomy had no effect on the volumetric density and absolute volume of the collagen and elastic fibers in the bladder wall of rats, or on the weight of the bladder. Estradiol replacement in castrated animals did not demonstrate any significant difference in the stereological parameters compared to the castrated group without hormonal replacement.

The effect of ovariectomy and long-term estrogen replacement on bladder structure and function in the rat

PURPOSE The use of estrogen replacement therapy for treating postmenopausal urinary incontinence is a controversial topic. We examined the behavioral, cystometric and histological changes that occur with long-term estrogen depletion and supplementation in rat bladders to determine the role of menopause in lower urinary tract dysfunction. MATERIALS AND METHODS A total of 40 female Sprague-Dawley rats were placed into 1 of 3 groups, including bilateral ovariectomy, bilateral ovariectomy plus estrogen replacement and control. The estrogen replaced group received a 0.25 mg. 16-week sustained release pellet (Innovative Research of America, Sanasota, Florida) placed subcutaneously. After surgery voiding frequency and volume were measured in 24-hour periods by placing animals in metabolic cages. After 16 weeks the rats underwent catheterization and continuous cystometry. The bladder was then removed and stained with Gomori trichrome. The collagen-to-smooth muscle density ratio was calculated for each specimen using current imaging software. RESULTS There was no significant difference in voiding patterns in the 3 groups, as measured by volume and voiding frequency. Cystometric data showed a trend toward higher voiding pressure, threshold pressure, baseline pressure and mean inter-voiding pressure in the ovariectomy group compared with the estrogen and control groups, although there was no statistical significance. Histological studies showed a higher mean collagen-to-smooth muscle ratio plus or minus standard deviation in the ovariectomy group (0.807 +/- 0.204) than in the ovariectomy plus estrogen replacement (0.709 +/- 0.118) and control (0.700 +/- 0.129) groups (p <0.05). Furthermore, when histological and cystometric data were compared for individual samples, we found a direct correlation of mean inter-voiding pressure (a measure of bladder instability) with the collagen-to-smooth muscle ratio (p <0.05). CONCLUSIONS Long-term estrogen replacement is beneficial for treating postmenopausal urinary incontinence.

The influence of ovariectomy and estrogen replacement on voiding patterns and detrusor muscarinic receptor affinity in the rat

A rat model of ovariectomy-induced voiding dysfunction was established and the effects of ovariectomy and subsequent estrogen replacement on the affinity of muscarinic receptors in the rat bladder were determined. Voiding frequency and spatial distribution patterns were documented in sham-operated (control), and ovariectomized (placebo- or estrogen-treated) rats. The ovariectomized rats had a significantly different urinating pattern, i.e. higher voiding frequency and less peripheral voiding than the sham-operated group, suggestive of urge incontinence. Using this model of voiding dysfunction, negative logs of dissociation constants of carbachol of the rat detrusor muscarinic receptors were then determined indirectly using the Furchgott's double-reciprocal method. Receptor affinities were not significantly different in all groups compared to control females. In conclusion, a model of ovariectomy-induced voiding dysfunction in ovariectomized rats was established, where bladder dysfunction occurred with no significant changes in the affinity of muscarinic receptors.

Muscarinic receptors of the urinary bladder: detrusor, urothelial and prejunctional

1. The parasympathetic nervous system is responsible for maintaining normal bladder function, contracting the bladder smooth muscle (detrusor) and relaxing the bladder outlet during micturition. 2. Contraction of the bladder involves direct contraction via M3 receptors and an indirect 're-contraction' via M2-receptors whereby a reduction in adenylate cyclase activity reverses the relaxation induced by beta-adrenoceptor stimulation. 3. Muscarinic receptors are also located on the epithelial lining of the bladder (urothelium) where they induce the release of a diffusible factor responsible for inhibiting contraction of the underlying detrusor smooth muscle. The factor remains unidentified but is not nitric oxide, a cyclooxygenase product or adenosine triphosphate. 4. Finally, muscarinic receptors are also located prejunctionally in the bladder on cholinergic and adrenergic nerve terminals, where M1-receptors facilitate transmitter release and M2 or M4-receptors inhibit transmitter release. 5. In pathological states, changes may occur in these receptor systems resulting in bladder dysfunction. Muscarinic receptor antagonists are the main therapeutic agents available for treatment of the overactive bladder, but whether their therapeutic effect involves actions at all three locations (detrusor, prejunctional, urothelial) has yet to be established.

Gender specificity of tolterodine on micturition and the diurnal variation of urine production of the conscious rat

OBJECTIVE

To evaluate the effect of the oral administration of tolterodine on the diurnal micturition characteristics of the male and female conscious rat, and to examine the relative effect of tolterodine in influencing water consumption and urine production.

MATERIALS AND METHODS

Baseline micturition volume and frequency characteristics of nine male and 10 female Sprague-Dawley age-matched adult rats (body weight 399 +/- 15 and 249 +/- 3 g, respectively) were evaluated over 24-h. Initial hydration conditions were standardized with an oral dose (5 mL) of water. Rats were subsequently placed in a metabolic cage and had free access to water. Micturition volume/frequency characteristics were derived from the measurements of voided volume (measured using a digital balance below the metabolic cage and connected to a computer). The total volume of water consumed over the 24 h was also measured. Two separate baseline studies were conducted, followed by the administration of a single oral dose of 1 mg/mL of tolterodine dissolved in 5 mL of water. The mean frequency of micturition and mean volume voided per micturition were computed in 3-h periods and plotted over the 24-h period. In addition, the mean values of the number of micturitions and voided volumes during the day/dark cycle were evaluated.

RESULTS

Baseline data showed that females (when corrected for body weight) consistently imbibed significantly more water (83%) than did male rats. Tolterodine did not significantly affect water consumption in the males but significantly reduced water consumption in females by 42%. Tolterodine did not significantly affect the amount of urine produced by male rats but significantly reduced the total amount of urine production in females by 26%. Tolterodine significantly increased the number of voids in male rats compared with baseline during the day but not during the night. More importantly tolterodine produce no significant effect on the volume voided per micturition in male rats either during the day or night cycle, but significantly decreased the volume voided per micturition in females.

CONCLUSIONS

These results suggest that the effect of tolterodine on micturition is gender-specific, suppressing water consumption and urine production in female but not male rats, and decreasing bladder volume. There is a possibility that the reported clinical effects of tolterodine arise through the suppression of fluid consumption.

Diabetes influences the effect of 17beta-estradiol on mechanical responses of rat urethra and detrusor strips

Estrogen deficiency is one of the factors involved in the stress incontinence in postmenopausal women, and estrogens have been used clinically in the treatment of urinary disorders during menopause. Sex hormones seem to be also involved in the diabetic changes of urinary bladder and urethra, because ovariectomy causes an increase in the micturition of streptozotocin-diabetic rats. In the present study diabetic and healthy female rats were used to investigate the effect of 17beta-estradiol on mechanical contractions to norepinephrine and to KCI and relaxations to ATP on isolated proximal urethral preparations as well as on contractions to ACh, ATP and KCl on detrusor smooth muscle strips. The data were compared with those obtained in OVX animals, with or without estradiol replacement. The present study showed that ovariectomy decreased the responses to ATP, NE and KCl in urethral preparations, and responses to ATP, ACh and KCl in bladder strips from both healthy and diabetic rats. Diabetes appeared to potentiate the effect of ovariectomy in both tissues. Estrogen replacement was able to recover functional responses in urethras of healthy rats. In diabetic rats, this treatment partially restored ATP-induced responses in both tissues, almost completely restored those to NE in urethra and those to ACh in bladder. This study clearly indicated that abnormalities of urethra and bladder function caused by ovariectomy can be restored by estrogen treatment also in diabetic animals, at least at an early stage of disease.

Age dependent response to exogenous estrogen on micturition, contractility and cholinergic receptors of the rat bladder

The age related effects of 17beta-estradiol (E) supplementation on micturition and contractility of ovariectomized rats (OVX) were evaluated. Studies were carried out in young, 2 month, and mature, 10 month old rats which were distributed into three groups: Sham-operated (SHAM), (OVX), and (OVX+E). Following treatment, urodynamic studies were performed followed by an in vitro bladder tissue evaluation. Urodynamic studies show age and time related changes in bladder function. The in vitro results show that the hormone deprived tissues of 2 months old rats had a decreased responsiveness to cholinergic stimulation; maximum contractile force occurred at 78% and 187% for the SHAM. The response from the OVX+E tissues was evident at 113%. E supplementation of the mature rats increased bladder contractile force to the same levels as SHAM (156% and 176%). The response of the mature OVX rats remained significantly below that of SHAM or OVX+E rats. Findings suggest that the impact of E on bladder function depends on age at which it is given. Differential response between young and mature to exogenous E indicates that endogenous estrogen plays a major role in the neuromuscular development of normal bladder function and micturition reflexes. Contractility data show that OVX in young rats irreversibly decreases the response of the bladder to cholinergic stimulation, suggesting that exogenous E partially restores function while in mature rats, exogenous E was able to reverse the effects of OVX.