Structural changes in the rat bladder after acute outlet obstruction

Effects of β3-adrenoceptor agonist on acute urinary retention in a rat model

PURPOSE

To investigate the protective effect of mirabegron on bladder dysfunction in an acute urinary retention rat model.

MATERIALS AND METHODS

Thirty-six 16-week Sprague-Dawley rats were assigned to the mirabegron and normal saline (N/S) groups. Each group of eighteen was divided into sub-groups of 6 for 30 min, 2 h, and 24 h. They were administered mirabegron (10 mg/kg) and N/S daily for 4 weeks, respectively. Mirabegron and N/S groups were divided into sub-groups of 6 rats for 30 min, 2 h, and 24 h. The changes in bladder blood flow were measured using laser Doppler (moorVMS-LDF2). Histopathological examination of the bladder and nitric oxide (NO) measurement were performed.

RESULT

During the urinary retention phase in the mirabegron group, it showed higher and rapider recovery of blood flow; the lowest at 19.5% ± 3.68% at 3 min, a significant recovery from the lowest value as 23.7 ± 3.4% at 10 min, than that in the N/S group; 15.1 ± 1.84% at 5 min, 23.7 ± 3.4% at 20 min, respectively (P < 0.05). At 30 min, 120 min, and 24 h after reperfusion, the recovery of blood flow in the mirabegron group was significantly higher than that in the N/S group (mirabegron: 41.1 ± 1.7%, 59.9 ± 7.2%, and 89.7 ± 4.4%, N/S: 31.3 ± 2.1%, 47.3 ± 4.5%, 83.9 ± 3.6%, respectively (P < 0.05)). NO levels tended to be higher in the mirabegron group; however, the difference was not statistically significant. Histological examination revealed that the mirabegron group showed recovery close to normal tissue after 24 h.

CONCLUSIONS

In an acute urinary retention rat model, mirabegron maintained and restored higher bladder blood flow, resulting in protective and recovery effect after acute urinary retention.

Neuroanatomic and behavioral correlates of urinary dysfunction induced by vaginal distension in rats

The aim of the present study was to use a model of simulated human childbirth in rats to determine the damage to genitourinary structures and behavioral signs of urinary dysfunction induced by vaginal distension (VD) in female rats. In experiment 1, the length of the genitourinary tract and the nerves associated with it were measured immediately after simulated human delivery induced by VD or sham (SH) procedures. Electroneurograms of the dorsal nerve of the clitoris (DNC) were also recorded. In experiment 2, histological characteristics of the bladder and major pelvic ganglion of VD and SH rats were evaluated. In experiment 3, urinary parameters were determined in conscious animals during 6 h of dark and 6 h of light before and 3 days after VD or SH procedures. VD significantly increased distal vagina width (P < 0.001) and the length of the motor branch of the sacral plexus (P < 0.05), DNC (P < 0.05), and vesical nerves (P < 0.01) and decreased DNC frequency and amplitude of firing. VD occluded the pelvic urethra, inducing urinary retention, hematomas in the bladder, and thinness of the epithelial (P < 0.05) and detrusor (P < 0.01) layers of the bladder. Major pelvic ganglion parameters were not modified after VD. Rats dripped urine in unusual places to void, without the stereotyped behavior of micturition after VD. The neuroanatomic injuries after VD occur alongside behavioral signs of urinary incontinence as determined by a new behavioral tool for assessing micturition in conscious animals.

Effect of different durations of overdistention on rat bladder function and morphology

We investigated the contribution of the duration of overdistention (DOD) to rat bladder function and morphology and explored its possible molecular mechanisms. Bladder overdistention was induced in male Sprague-Dawley rats (200-250 g) by an infusion of saline. Forty rats were divided into 5 groups submitted to different DOD, i.e., 1, 2, 4, and 8 h, and control. Bladder function was evaluated by cystometry. Morphological changes were observed by light and transmission electron microscopy. Compared to control (44.567 ± 3.472 cmH2O), the maximum detrusor pressure of groups with 2-, 4- and 8-h DOD decreased significantly (means ± SEM): 32.774 ± 3.726, 31.321 ± 2.847, and 29.238 ± 3.724 cmH2O. With the increase of DOD, inflammatory infiltration and impairment of ultrastructure were more obvious in bladder tissue. Compared to control (1.90 ± 0.77), the apoptotic indexes of groups with 1-, 2-, 4-, and 8-h DOD increased significantly (6.47 ± 2.10, 10.66 ± 1.97, 13.91 ± 2.69, and 18.33 ± 3.28%). Compared to control (0.147 ± 0.031/0.234 ± 0.038 caspase 3/β-actin and Bax/Bcl-2 ratios), both caspase 3/β-actin and Bax/Bcl-2 ratios of 1-, 2-, 4-, and 8-h DOD increased significantly (0.292 ± 0.037/0.508 ± 0.174, 0.723 ± 0.173/1.745 ± 0.471, 1.104 ± 0.245/4.000 ± 1.048, and 1.345 ± 0.409/8.398 ± 3.332). DOD plays an important role in impairment of vesical function and structure. With DOD, pro-apoptotic factors increase and anti-apoptotic factors decrease, possibly contributing to the functional deterioration and morphological changes of the bladder.

Downregulation of TWIK-related arachidonic acid-activated K+ channel in the spinal cord of rats after complete bladder outlet obstruction

OBJECTIVES

To study the altered expression of TWIK-related arachidonic acid-activated K(+) channel in the L6-S1 spinal cord of rats after complete bladder outlet obstruction, and to investigate the role of TWIK-related arachidonic acid-activated K(+) channel in the neurogenic mechanism of bladder dysfunction.

METHODS

Female Sprague-Dawley rats were randomly divided into a complete bladder outlet obstruction group and a sham-operated control group. Cystometry was carried out and tissues of L6-S1 spinal cord were obtained for detection of TWIK-related arachidonic acid-activated K(+) channel mRNA and protein by real-time polymerase chain reaction, western blot and immunohistochemistry.

RESULTS

The bladder outlet obstruction rat model was established. Real-time polymerase chain reaction, western blot and immunohistochemistry showed that the expression of TWIK-related arachidonic acid-activated K(+) channel was lower in the L6-S1 spinal cord of the bladder outlet obstruction rats, compared with the control rats.

CONCLUSIONS

Downregulation of TWIK-related arachidonic acid-activated K(+) channel might enhance the excitability of the neurons and increase the sensitivity of the bladder, probably providing a new study model of overactive bladder secondary to bladder outlet obstruction.

Smooth muscle trans-membrane sarcoglycan complex in partial bladder outlet obstruction

The urinary bladder experiences both distension and contraction as a part of the normal filling and emptying cycle. To empty properly, tension generated intracellularly in a smooth muscle cell must be smoothly and efficiently transferred across its sarcolemma to the basement membrane, which mediates its binding to both the extracellular matrix and to other cells. As a consequence of urethral obstruction, the bladder cannot generate appropriate force to contract the organ, thereby leading to inefficient emptying and associated sequelae. In this study, an animal model of urethral obstruction was utilized to study the membrane-associated structures that transfer tension across the sarcolemma of bladder smooth muscle cells. Immunohistochemical localization of key components of the smooth muscle tension transfer apparatus (TTA) was performed utilizing specific antibodies against:(1) the alpha-chains of type IV collagen, a basement membrane component, and (2) beta-sarcoglycan, an integral membrane protein that is a participant in the physical linkage between the cytoskeleton and the basement membrane. We demonstrate, in obstructed animals, that there is a pronounced disruption of the TTA with a physical displacement of these two components that can be demonstrated at the level of the light microscope using scanning confocal microscopy. Electron microscopy further demonstrates significant increases in the size of the junctional plaques between smooth muscle cells.

Effect of vaginal distension on blood flow and hypoxia of urogenital organs of the female rat

Vaginal delivery of children causes traumatic injury to tissues of the pelvic floor and is correlated with stress urinary incontinence; however, the exact mechanism of organ and tissue injury leading to incontinence development is unknown. The purpose of this project was to test the hypothesis that vaginal distension results in decreased blood flow to, and hypoxia of, the urogenital organs responsible for continence, which would suggest an ischemic and/or reperfusion mechanism of injury. Thirteen female rats underwent vaginal distension for 1 h. Thirteen age-matched rats were sham-distended controls. Blood flow to the bladder, urethra, and vagina were determined using a microsphere technique. Hypoxia of these organs was determined by immunohistochemistry. Blood flow to all three organs was significantly decreased just before release of vaginal distension. Bladder blood flow decreased further immediately after release of vaginal distension and continued to be significantly decreased 15 min after the release. Blood flow to both the urethra and vagina tripled immediately after release, inducing a rapid return to normal values. Vaginal distension resulted in extensive smooth muscle hypoxia of the bladder, as well as extensive hypoxia of the vaginal epithelium and urethral hypoxia. Bladders from sham-distended rats demonstrated urothelial hypoxia as well as focal hypoxic areas of the detrusor muscle. We have clearly demonstrated that vaginal distension results in decreased blood flow to, and hypoxia of, the bladder, urethra, and vagina, supportive of hypoxic injury as a possible mechanism of injury leading to stress urinary incontinence.

Protective effect of an oral endothelin converting enzyme inhibitor on rat detrusor function after outlet obstruction

PURPOSE

Endothelin (ET)-1, one of the most potent vasoconstrictors known, is converted from its less potent precursor big ET by the endothelin converting enzyme (ECE). In vitro studies suggest that ET has an important role in smooth muscle growth after bladder outlet obstruction (BOO). We investigated the effect of an orally administered ECE inhibitor by cystometry in conscious rats with and without BOO.

MATERIAL AND METHODS

BOO was produced in female rats by a standardized method and the animals were divided into 2 groups. One group received the ECE inhibitor WO-03028719 and the remaining animals received vehicle daily by oral gavage. Five sham operated animals served as controls and were treated with WO-03028719. Two weeks after surgery cystometry was performed.

RESULTS

BOO led to a significant increase in bladder weight in vehicle treated animals and a nonsignificant increase in the treatment group. Micturition interval and volume increased in each obstructed group. Micturition pressure was significantly decreased in the vehicle group but unchanged in the BOO treatment group. Residual urine occurred in 4 of 11 BOO vehicle animals but not in the sham operated or BOO treatment group. Spontaneous nonvoiding bladder contractions occurred in 37% of BOO treatment animals but in 82% of the BOO vehicle group. Voiding contractions were markedly prolonged in the BOO vehicle group, while they were normal in the BOO treatment group.

CONCLUSIONS

ECE inhibition did not prevent an increase in bladder weight after BOO but it appeared to have a beneficial effect on detrusor function and decrease detrusor overactivity in conscious rats.

THE MOLECULAR GENETIC BASIS OF MITOCHONDRIAL MALFUNCTION IN BLADDER TISSUE FOLLOWING OUTLET OBSTRUCTION

PURPOSE

Bladder dysfunction following partial outlet obstruction is a frequent consequence of benign prostatic hyperplasia and an increasingly common problem given the aging of the general population. Recent studies from this and other groups have begun to elucidate the molecular bases for the well described physiological malfunctions that characterize this clinical entity. We summarized and synthesized that information.

MATERIALS AND METHODS

Using modern methods of molecular genetics, including real-time polymerase chain reaction, real-time reverse transcriptase-polymerase chain reaction and others, as well as traditional experimental techniques such as electron microscopy we and others examined the transcriptional profile, morphology, etc of bladder smooth muscle mitochondria in experimental models of outlet obstruction.

RESULTS

Data from many studies have demonstrated that aberrant gene expression in the mitochondrial and mitochondria related nuclear genetic systems underlies the loss of compliance and other attributes of bladder dysfunction following outlet obstruction. Such aberrant transcriptional characteristics engender loss of function in the electron transport and oxidative phosphorylation systems. Morphological studies of mitochondria in the animal model systems support this conclusion.

CONCLUSIONS

In large part the loss of function in bladder smooth muscle following outlet obstruction results from the attenuation of mitochondrial energy production. In this article we reviewed and synthesized all available experimental observations relevant to this problem and we suggest future lines of inquiry that should prove fruitful in developing new strategies to treat the condition.