Effect of distension on adrenergic innervation of the rat urinary bladder

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.

Purinergic signalling in the urinary tract in health and disease

Purinergic signalling is involved in a number of physiological and pathophysiological activities in the lower urinary tract. In the bladder of laboratory animals there is parasympathetic excitatory cotransmission with the purinergic and cholinergic components being approximately equal, acting via P2X1 and muscarinic receptors, respectively. Purinergic mechanosensory transduction occurs where ATP, released from urothelial cells during distension of bladder and ureter, acts on P2X3 and P2X2/3 receptors on suburothelial sensory nerves to initiate the voiding reflex, via low threshold fibres, and nociception, via high threshold fibres. In human bladder the purinergic component of parasympathetic cotransmission is less than 3 %, but in pathological conditions, such as interstitial cystitis, obstructed and neuropathic bladder, the purinergic component is increased to 40 %. Other pathological conditions of the bladder have been shown to involve purinoceptor-mediated activities, including multiple sclerosis, ischaemia, diabetes, cancer and bacterial infections. In the ureter, P2X7 receptors have been implicated in inflammation and fibrosis. Purinergic therapeutic strategies are being explored that hopefully will be developed and bring benefit and relief to many patients with urinary tract disorders.

Chronic cyclic bladder over distention up-regulates hypoxia dependent pathways

PURPOSE

Bladder over distention secondary to anatomical or functional obstruction can eventually lead to pathological changes, including decreased elasticity and contractile dysfunction. We hypothesized that chronic bladder distention in a murine model would activate hypoxia dependent signaling pathways despite intermittent relief of distention.

MATERIALS AND METHODS

Female C57Bl/6 mice were oophorectomized at age 5 to 6 weeks and underwent urethral catheterization and 90-minute bladder distention. Acute and chronic time points were evaluated. Bladder tissue was harvested for hematoxylin and eosin, and immunohistochemical staining with the hypoxia markers Glut-1 (EMD Millipore, Merck, Darmstadt, Germany) and Hypoxyprobe™-1. Bladder tissue was also harvested for real-time polymerase chain reaction and oxidative stress measurement. Hypoxia polymerase chain reaction arrays were done to determine changes in gene expression. Oxidative stress was measured using F2-IsoP. Functional bladder changes were evaluated using voided urine blots.

RESULTS

After acute distention and 5 consecutive distentions, bladders showed marked inflammatory changes on hematoxylin and eosin staining, and evidence of tissue hypoxia on immunohistochemistry. Quantitative real-time polymerase chain reaction revealed up-regulation of hypoxia and oxidative stress related genes, including Hif1a, Arnt2, Ctgf, Gpx1 and Hmox1. Measurements of oxidative stress with F2-IsoP did not change. Voided urine blots before and after bladder distention showed marked changes with an overactive voiding pattern.

CONCLUSIONS

Chronic bladder distention is possible in the female mouse. It generates hypoxic injury, as characterized functionally by increased voiding patterns. This bladder injury model might more closely replicate bladder dysfunction in patients with poor bladder emptying due to neurological disease, including those noncompliant with intermittent catheterization.

Beneficial effect of preconditioning on ischemia–reperfusion injury in the rat bladder in vivo

We investigated the effect of preconditioning on ischemia-reperfusion injury in the rat bladder. Rat abdominal aorta was clamped with a small clip to induce ischemia-reperfusion injury in the bladder. Twelve-week-old male SD rats were divided into three groups; sham-operated control (Cont), 30 min ischemia-60 min reperfusion (IR) and three times of 5 min ischemia and then 30 min ischemia-60 min reperfusion (PC) groups. The bladder functions were estimated by cystometric and functional studies. Contractile response curves to increasing concentrations of carbachol were constructed in the absence and presence of various concentrations of subtype selective muscarinic antagonists, i.e. atropine (non-selective), pirenzepine (M1 selective), methoctramine (M2 selective), and 4-DAMP (M1/M3 selective). We also measured tissue levels of malonaldehyde (MDA) and examined possible histological changes in these rats' bladders. Preconditioning partially prevented the reduction of bladder dysfunction induced by ischemia-reperfusion. Estimation of the pA2 values for atropine, pirenzepine, methoctramine, and 4-DAMP indicates that the carbachol-induced contractile response in bladder dome is mediated through the M3 receptor subtype in all groups. The MDA concentration in the IR group was significantly larger than that of the control group, and preconditioning significantly reduced MDA production in the bladder. In histological studies, the ischemia-reperfusion with or without preconditioning caused infiltration of leukocytes and rupture of microcirculation in the regions of submucosa and smooth muscle without a corresponding sloughing of mucosal cells. Our data indicate that preconditioning has a beneficial effect on ischemia-reperfusion injury in the rat bladder.

The role of free radicals and nitric oxide in the ischemia–reperfusion injury mediated by acute bladder outlet obstruction

Free-radical generation and nitric oxide (NO) generation were detected in the rat bladder following acute bladder outlet obstruction (BOO), and the results were compared with those for vascular ischemia and reperfusion (I-R). Forty male Sprague Dawley rats were used. In the acute BOO plus I-R group (group 1), rats were catheterized with a 3-Fr catheter and an inflated balloon was positioned at the bladder neck. The bladder was overdistended after administration of Ringer solution and furosemide (12 mg/kg, each) for 60 min, and was then drained to allow reperfusion for 30 min. In the acute BOO plus nerve stimulation group (group 2), the pelvic nerve was stimulated in the distended bladder for 60 min (5 s every 5 min, 10 V/0.1 ms, 20 Hz). Pelvic nerve stimulation was performed in nonobstructed animals in group 3. In the I-R group (group 4), the distal aorta was occluded for 60 min followed by reperfusion for 30 min. Sham-operated animals served as the control group (group 5). At the end of the protocols, the levels of hydroxyl and superoxide radicals and NO levels were measured in the bladder tissues with luminol- and lucigenin-enhanced chemiluminescence methods. The results were compared by a one-way analysis of variance test. The levels of hydroxyl radicals were not significantly different between the study groups. In contrast, superoxide radicals and NO levels were significantly increased in both group 1 and group 4 compared with those in control animals (P<0.05 for all comparisons). Superoxide radical generation in group 2 was comparable to the levels in group 1 (P>0.05), whereas NO levels were substantially lower than in group 1 (P=0.06). In summary, vascular I-R causes significant oxidative damage to the bladder. Acute BOO with overdistension of the bladder mimics the effects of true vascular I-R injury. The NO pathway has possibly a major role in I-R-induced bladder damage. Prolonged BOO may therefore significantly enhance the oxidative damage to the bladder and further accentuate the effects of generalized atherosclerotic processes in the elderly adult.

A rat model for functional characterization of pregnancy-induced denervation and postpartum reinnervation in the myometrium and cervix: a superfusion study

The pregnancy-induced rapid degeneration of the adrenergic nerves innervating the uterus is a well-known but poorly understood phenomenon. Since most of the published investigations were carried out by histological assay, our aim was to describe the loss of the adrenergic function during pregnancy and the reinnervational procedure in the postpartum period. Myometrial and cervical samples from rats were loaded with [3H]noradrenaline and then transferred into a chamber for superfusion. After a wash-out period, fractions were collected. The fifth and fifteenth fraction tissues were stimulated with an electric field. The [3H]noradrenaline contents of the fractions were determined, together with the amount remaining in the tissue. The myometrial [3H]noradrenaline release was substantially decreased in early pregnancy, and absent in the late stage. Differences in release profile were detected between the implantation sites and the interimplantation areas. As a refinement of the results of previous histochemical studies, the noradrenergic functions of the cervix were found to be deeply affected in the early postpartum period. The pregnancy-induced denervational procedure can be followed by means of a superfusional technique after [3H]noradrenaline loading. As our technique is considered to be similar in sensitivity to histological methods, superfusion can be regarded as a model for functional investigations of pregnancy-induced denervation.

Hypoxia preconditioning attenuates bladder overdistension-induced oxidative injury by up-regulation of Bcl-2 in the rat

We explored whether hypoxic preconditioning minimizes oxidative injury induced by overdistension/emptying in the rat bladder. For hypoxic preconditioning, female Wistar rats were placed in a hypobaric chamber (380 Torr) 15 h day(-1) for 28 days. Overdistension was induced by infusion of two times the threshold volume of saline into the bladder and was maintained for 1 or 2 h, followed by drainage/emptying. During overdistension (ischaemia) and emptying (reperfusion) periods, a bursting increase of reactive oxygen species (ROS) from the bladder was originated from the large numbers of infiltrating leucocytes and scattered resident cells, including urothelial, submucosal, and smooth muscle cells. ROS impaired the voiding function by a reduction of bladder afferent and efferent nerve activity and bethanecol- or ATP-induced detrusor contraction. ROS enhanced pro-apoptotic mechanisms, including increases in the Bax/Bcl-2 ratio, CPP32 expression, and poly(ADP-ribose) polymerase (PARP) fragments with subsequent apoptotic cell formation in the insulted bladders. Hypoxia preconditioning up-regulated Bcl-2 expression in the bladder and significantly reduced the levels of ROS and apoptosis detected in the overdistension/emptying bladders and preserved partial voiding function. Bcl-2 up-regulation by hypoxia preconditioning contributes protection against overdistension/emptying-induced oxidative stress and injury in the bladder.

Structural and vascular response of normal and obstructed rabbit whole bladders to distension

OBJECTIVES

To investigate the structural and morphologic effect of distension after partial outlet obstruction in rabbits.

METHODS

Thirty male New Zealand white rabbits were separated into two groups: control (sham) and partial outlet obstruction (3 weeks). Three rabbits from each group were distended to 5%, 25%, 50%, 100%, and 125% of capacity. Each bladder was fixed at the volume in buffered formalin for 6 to 8 hours. Sections of dorsal and ventral bladder were blocked, and cross sections were evaluated. Quantitative morphometry was performed, and CD31 immunohistochemistry was used to characterize the vascularity.

RESULTS

Partial outlet obstruction resulted in increased bladder weight and capacity and increased thickness of the mucosa, submucosa, detrusor, and serosa. In the control bladder, the greatest thinning was seen between 5% and 25% capacity, and in the obstructed group, the greatest thinning occurred between 25% and 50%. The level of vascular collapse was significantly greater for the control bladders than for the obstructed bladders at all levels of distension. Finally, the obstructed bladders showed a significantly greater level of vascularity in the submucosa than the control bladders.

CONCLUSIONS

Normal bladder distension resulted in significant morphologic changes when the bladder was distended to 25% of capacity but changed relatively little between 25% and 125%. However, distension of the obstructed bladder resulted in significant morphologic changes when the bladder was distended from 25% to 50% of capacity but changed relatively little between 50% and 125%.

The functional and structural response to distention of the rabbit whole bladder in vitro

PURPOSE

We investigated the effects of distention on intravesical pressure generation in response to stimuli in relation to its effects on bladder wall thickness and morphology.

MATERIALS AND METHODS

A total of 25 New Zealand White rabbits were separated into 5 groups of 5 each. Each in vitro whole bladder preparation was filled with saline to 5% (undistended), 25%, 50%, 100% or 125% capacity (60 ml.). The effects of field stimulation, adenosine 5'-triphosphate, carbamylcholine chloride (carbachol) and KCl on intravesical pressure generation were determined. Additional bladders were similarly distended (3 at each percent of capacity), fixed in formalin and evaluated by semiquantitative morphometry.

RESULTS

Pressure generation in response to field stimulation was maximal at 5% of capacity and it decreased progressively thereafter. Compared with the responses of undistended bladders, at 25% capacity the response to carbachol increased and then decreased progressively above 25%. Distention had no significant effect on the response to KCl. Interestingly pressure generation in response to adenosine 5'-triphosphate was increased more than 4-fold at 25% bladder capacity compared with 5% and it did not change significantly thereafter. Bladder wall thickness was decreased more than 50% at 25% capacity and by an additional 12% at 125% capacity. The greatest thinning was observed in the mucosa compared with the submucosa and muscularis.

CONCLUSIONS

Bladder distention significantly reduced pressure generation in response to field stimulation only, indicating that distention reduced the effectiveness of synaptic transmission without altering muscarinic receptor function or membrane depolarization. The greatest change (decrease) in the response to field stimulation occurred between 5% (undistended) and 25% capacity, which was the change in distention that most affected bladder wall thinning.

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.

The influence of acute overdistension on rat bladder function and DNA synthesis

Prolonged micturition problems are often encountered after long-term bladder overdistension caused by urinary retention. In animal studies, damage to the bladder wall innervation has been found following overdistension. Experimentally, acute overdistension has also been implicated in the pathogenesis of the response to partial outlet obstruction. In the present study we investigated the influence of overdistension on micturition volume and frequency, on in vitro bladder function using the whole bladder model and on 3H-thymidine uptake, localization and DNA synthesis. Overdistension was induced for 3 hours by forced diuresis and balloon obstruction. Another group of rats was catheterized for 3 hours but received no diuretic, nor was the balloon inflated. An additional group of controls was neither anesthetized nor catheterized. Overdistension caused a gradual increase in bladder mass which was maximal at 7 days. During the first 24 hours following overdistension, the frequency of micturition decreased, but normalized thereafter. A progressive decrease in the response to field stimulation was noted between 16 hours and 7 days following overdistension and remained at this level until 21 days. There were, however, no significant differences in the responses to carbachol, ATP and KCl. There was a 30% reduction in the ability of field stimulation to empty the bladder 16 hours after overdistension, but no impairment of the emptying ability of carbachol. Overdistension was followed by a significant increase in 3H-thymidine uptake, which was maximal at 2 days. 3H-thymidine labelling increased rapidly after overdistension and was maximal within 16 hours in the urothelium. In smooth muscle, connective tissue and lamina propria, maximal labelling occurred at 2 days. Catheterization alone caused a mild distension which was associated with a small, but statistically significant, increase in 3H-thymidine incorporation into DNA within 16 hours. The labelling was located primarily in the urothelium. Overdistension causes a proliferative reaction within the bladder wall. Its initial effects occur within the urothelium, and the later involvement of the subendothelial smooth muscle and connective tissue is directly proportional to the degree of bladder distension. Three weeks following overdistension, the bladder's functional state was not completely recovered, although the urinary bladder was found to have a good capacity to adapt and compensate for the stress-induced changes caused by overdistension. It is, therefore, clear that overdistension may have long-lasting effects on the bladder.

Combined trypan blue and glyoxylic acid-induced catecholamine fluorescence in the female rat urinary bladder after distension

The effect of short-term urinary bladder distension on bladder perfusion and adrenergic innervation was studied in Sprague-Dawley rats. Distension was induced for three hours by forced diuresis and balloon obstruction. A 2% solution of trypan blue was injected into the tail vein 12, 24, 36 and 48 hours after distension and the animals were killed 5-10 min after the injection. Whole thick biopsies were taken from the dome, anterior body and base. A combination of trypan blue and catecholamine fluorescence (GIF method) was used to correlate the distension induced changes in blood vessel perfusion and permeability with changes in adrenergic innervation. Both ischaemic damage and adrenergic hypoinnervation were observed after distension. Later marked extravasation of trypan blue was observed in the whole bladder after 12 hours and after 24 hours distension the dome was almost necrotic in appearance and highly ischaemic. After 36 hours a few exploded small, intensely fluorescent cells (SIF cells) were found to be scattered along the blood vessels, and degranulated mast cells had invaded the anterior body and dome. The adrenergic hypoinnervation reached its maximum 48 hours after distension. The hypoinnervation and possibly also the damage to SIF cells, would seem to be related to ischaemia during distension, probably attributable in turn to overstretching of the organ and its blood vessels. This may provide an explanation for the prolonged micturition problems found after bladder overdistension.

The effect of acute distension on vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY) and substance P (SP) immunoreactive nerves in the female rat urinary bladder

The effect of acute distension on vasoactive polypeptide (VIP)-, neuropeptide Y (NPY)- and substance P (SP)-immunoreactive nerves in the wall of the urinary bladder was investigated. At the age of 3 months, 25 female albino rats underwent forced diuresis combined with balloon obstruction to achieve maximal distension for 3 h. A modified, indirect immunofluorescence detection method was applied 2 days, 7 days and 21 days after distension. A marked, extensive depletion of VIP, NPY- and SP-immunoreactive nerves was observed after distension. This disturbance was reversible, and increased fluorescence of VIP-, NPY- and SP-immunoreactive nerve fibres compared with control specimens was seen in bladder specimens taken even as soon as 21 days after distension. This transient depletion of peptidergic innervation may partly explain the prolonged voiding problems that often occur after acute urinary retention. The depletion of sensory nerves containing SP shortly after distension may explain the transient benefit obtained from distension therapy in patients with painful bladder disease. It is suggested that the increased SP activity during the recovery phase may be related to neurogenic inflammation.

Effect of acute distension on cholinergic innervation of the rat urinary bladder

The effect of short-term urinary bladder distension on its cholinergic innervation was studied in Sprague-Dawley rats. Distension was induced for 3 h by forced diuresis and balloon outlet obstruction, and whole thick biopsy specimens were taken from the dome and lateral side of the anterior body 2, 7 and 21 days afterwards. The acetylcholinesterase (AChE) method was used to demonstrate the cholinergic nerves in the distended bladder wall. Cholinergic hypoinnervation was observed 7 days after the distension, persisting up to 21 days, although AChE-reactive nerves were then observed to be more numerous. The distribution of hypoinnervation was uneven, being more marked in the lateral side of the anterior body than in the dome. The distribution of AChE-reactive nerves varied even in the same biopsies, with areas of total hypoinnervation occurring next to areas of slightly diminished innervation. This was especially true 21 days after distension. The findings indicate transient damage to the cholinergic innervation, which may in turn explain the prolonged voiding difficulties often seen after catheterization of an overdistended bladder in a patient with urinary retention. The short-lasting effect of bladder dilatation therapy used to treat detrusor instability or interstitial cystitis may be due to the fairly rapid regeneration of cholinergic innervation.

Changes in the noradrenaline content of the female rat urinary bladder after transient acute overdistension

The effect of transient acute overdistension produced by forced diuresis and outflow occlusion was examined in female Sprague-Dawley rats. Their bladders were distented for three hours and studied at selected intervals during the postoperative period using high performance liquid chromatography (HPLC) for the exact measurement of tissue noradrenaline. Biopsies were taken from the bladder dome and anterior body 10 hours, 2 days, 7 days and 21 days after overdistension. A reduction in NA concentration was found in both the dome and anterior body at 2 to 21 days after distension. The results demonstrated at least partial transient damage to the adrenergic nerves containing NA. The primary success of the distension therapy used to treat bladder instability may be due to this injury.