Correlation between bladder compliance and the content of detrusor collagen fibers

Hi-Yn Zhng，Hi-Xu Ji，Wei Li，Jin-Hu Zhng

aSanquan Medical College，Xinxiang，Henan，453000，China

bXinxiang Medical University，Xinxiang，Henan，453000，China

Original article

Correlation between bladder compliance and the content of detrusor collagen fibers

Hai-Yan Zhanga，Hai-Xu Jia，Wei Lia，Jin-Hua Zhangb，*

aSanquan Medical College，Xinxiang，Henan，453000，China

bXinxiang Medical University，Xinxiang，Henan，453000，China

A R T I C L E I N F O

Article history：

Received 23 November 2015

Received in revised form

27 December 2015

Accepted 26 January 2016

Available online 23 June 2016

Bladder outlet obstruction（BOO）

Detrusor

Collagen fibers

Compliance

Rats

Experimental study

Objective：To explore the possible correlation between bladder compliance（BC）and the changes in detrusor collagen fiber content after bladder outlet obstruction（BOO）.

Methods：Ninety healthy female Sprague-Dawley（SD）rats were enrolled in this experiment and divided into an experimental group and a control group randomly，using the randomizing table method，with 70 rats in the experimental group and 20 rats in the control group.Six weeks after BOO modeling was established，BC was evaluated through bladder testing.Bladder tissues were then fixed and embedded in paraffin.The tissues were cut into thin slices，followed by Masson staining and observation under a microscope.

Results：Compared with the control group，the BC of the experimental group rats increased，and the difference had statistical significance（P＜0.05）；the content of detrusor collagen fibers of the rats in the experimental group increased significantly compared to the control group.

Conclusions：The content of detrusor collagen fibers increased significantly after BOO，and BC was higher.

?2016 Shanxi Medical Periodical Press.Publishing services by Elsevier B.V.This is an open access article under the CC BY-NC-ND license（http：//creativecommons.org/licenses/by-nc-nd/4.0/）.

1.Introduction

With the advent of a gray society，the incidence of benign prostatic hyperplasia has gradually increased in recent years.The major clinical manifestations in males are frequent urination，urgent need to urinate，urinary retention，etc.Many of the lower urinary tract symptoms caused by benign prostatic hyperplasia are caused by changes in bladder function resulting from bladder outlet obstruction（BOO）.Clinical investigation indicates that approximately 1/3 of the patients with benign prostatic hyperplasia still have voiding dysfunction after the relief of the obstruction.1Therefore，the focus shifts from the prostate to the bladder.Some scholars believe that the increase of the content of collagen fibers in detrusor cells is one of the main causes of voiding dysfunction.2In this study，we observed the changes in the content of collagen fibers of rats after BOO，as well as the detrusor contractility，and discussed the correlation between the collagen fiber content and detrusor contractility.

2.Methods

2.1.The model of bladder outlet obstruction（BOO）

The BOO animal model was established by inserting a 1-mm epidural anesthesia catheter into the rat's bladder after anesthesia with 1%pentobarbital sodium and then performing partial ligation of the perineal urethra using 4-0 silk thread in the experimental group.The epidural anesthesia catheter can be pulled out easily.The anesthesia and operation were the same in the control group，but the urethral canal was not ligated.

2.2.Filling cystometry

The sutures were taken out，and a 1 mm epidural anesthesia catheter was inserted into the bladders of experimental group rats for cystometry after anesthesia with 20%urethane.The filling velocity was 12 mL/h，and the infusion was stopped when perfusion liquid was found flowing out from the urethral opening. Bladder leakage point pressure（BLPP）and bladder capacity were recorded.

http：//dx.doi.org/10.1016/j.cnre.2016.01.003

2095-7718/?2016 Shanxi Medical Periodical Press.Publishing services by Elsevier B.V.This is an open access article under the CC BY-NC-ND license（http：//creativecommons. org/licenses/by-nc-nd/4.0/）.

2.3.Masson staining

Rat bladder specimens were fixed with ethanol dehydration and embedded in regular paraffin.They were then sliced，stained，and observed under a light microscope.With the use of Masson staining，detrusor muscle fibers were stained red，collagen fibers were stained blue，cell nuclei were stained blue-brown，and red cells were stained brownish red.

2.4.Statistical analysis

3.Results

3.1.Establishment of BOO model

Experimental group：Of the 70，4 rats died of anesthesia，2 rats died due to tight ligation，another 2 died of infection.Successful model was established in 62 rats，consisting of 48 in the unstable bladder group（DI）and 14 in the stable bladder group（DS）.The modeling success rate was 75.61%.All the 20 rats in the control group survived.

3.2.Changes in BC

BC is the ratio of the increment of detrusor and the increment of bladder volume.According to the definition of the International Continence Society（ICS），it can be expressed as C=ΔV/ΔP.Of which，C is compliance，ΔP is the increment of pressure，andΔV is the increment of bladder volume when pressure increases byΔP. Bladder pressure measurement showed that all the BLPPs of the experimental group increased to a certain extent，and the differences of the BLPPs between the groups had statistical significance（P＜0.05）（Table 1）.It was found that the experimental group could be divided into a high-compliance group（53 cases）and a lowcompliance group（9 cases）（Table 1）.

3.3.Masson staining

The bladder specimens of the control group ratsshowed that the space between the red-stained detrusor fascicles was filled with green-stained rich collagen fibers，with compact structure of bladder wall and rich collagen fibers under the mucous membrane（Fig.1）.The bladder specimens of the experimental group rats showed that the transverse fascicles were plump，the detrusor fascicles were disorderly and loose，the space between the fascicles was obviously wider，there was less collagen，and the volume of the fascicles was larger.The green-stained collagen between the fascicles was obviously less，as was that under the mucous membrane（Fig.2）.

Table 1 Comparison of the BLPPs and BCs in different groups

Note：*Compared with control group，P＜0.05；**Compared with DI group，P＜0.05.

BC mL/cm H2O DI 40.467±3.576* 0.117±0.011*DS 32.680±1.774** 0.086±0.026**Control group 16.964±1.738 0.061±0.007 F value 473.364 277.940 P 0.002 0.013 Group BLPP cm H2O

4.Discussion

4.1.About the animal model

我見(jiàn)過(guò)一位父親，一心要把孩子培養(yǎng)成牛人，于是早早給他買(mǎi)《曾國(guó)藩》《胡雪巖》；另一位母親，則憂心忡忡，認(rèn)定《傲慢與偏見(jiàn)》《紅樓夢(mèng)》都只會(huì)把她的花季女兒教壞，索性根本不讓女兒看“閑書(shū)”：“有那時(shí)間背背單詞不好嗎？”

There are many reports about the BOO animal model，adopting the same or different laboratory animals and modes，but the key point is to avoid to the greatest extent the influences on detrusor functions from non-obstruction factors.The most commonly adopted method is ligation，in which ligature of the urethra with silk thread causes artificial urethrostenosis，and then BOO.This method is easy，precise，and reliable，with lower operative strike on animals and a higher success rate.

In the modeling of this experiment，perineal-urethral ligation is adopted.Perineal-urethral ligation is easier to operate than the ligation of the bladder-neck urethra，causes less bleeding，and leaves a smaller scar.The operation does not require dissection of the pelvic cavity；avoiding nervous damage and pelvic pathologic adhesion and making the obstruction of the outflow tract steadier.3In addition，preliminary experimentsprovethat，compared with normal rats，the wet weight and volume of the modeling rats are significantly increased（P＜0.05），with reliable obstruction effect.

4.2.Mechanism of the hyperplasia of collagen after BOO

Most researchers believe that the increase of internal bladder pressure after BOO is the cause of collagen synthesis，but the details are still unknown.4-6Study showed that bladder smooth muscles consisted of both synthesis type and contracting type.The smooth muscles of the synthesis type can turn into myofibroblasts and then collagen fibers or elastic fibers.As BOO continues，part of the smooth muscles of the contracting type may turn into that of synthesistype，lowering bladdercontractility.7In addition，increased internal bladder pressure may cause the high expression of TGF-β1，which is generally accepted as the cytokine having the closest relationship with collagen metabolism，mainly acting on the transcription and translation，and promoting the formation and deposition of collagen.8The changes in the form and function of the bladder after BOO have drawn more and more attention，and the hyperplasia of bladder collagen fibers is an important cause of obvious change of the bladder with outlet obstruction，as well as triggering or deteriorating other pathological and physiological changes.

4.3.Correlation between the content of detrusor collagen fibers and the BC

For normal bladder detrusors，in the early stage of filling，the bladder volume increased very slightly in internal pressure due to the elasticity，viscoelasticity，reflex bladder，and other bladder effects.Even the urination volume remained at a relatively lowpressure range，with good compliance.Only once the bladder reached a certain volume of fullness，due to micturition reflex，the detrusor generated continued strong contractions，causing the pressure to rise rapidly.However，BOO may cause detrusor cell changes in structure and organization，thus affecting the BC.9

Abnormal bladder compliance can be divided into high compliance，low compliance，andmixedcompliance.Highcompliance bladder is often seen during the period of the decompensation of detrusor.After six weeks of modeling in this experiment，53 rats in the experimental group had increased bladder volume and increased compliance，compared with the low-compliance bladder control group，the differences were statistically significant（P＜0.05）.It is believed after analysis that BOO modeling leads to hyperplasia of bladder collagen，but the detrusor collagen production was slower than the speed of detrusor hyperplasia，so although there is an absolute increase in the number of collagen，the proportion of bladder detrusor collagen decreases，leading to a decrease in the relative collagen content.Some studies show that after BOO，the bladder uses its unused muscles reserves to increase the contractile force and the number of muscle cells in order to compensate its function.The content of bladder collagen increases，but compared with the hypertrophy and hyperplasia of detrusor of bladder and the increase of the volume and the number of smooth muscles，it has less impact on bladder function.10

Low-compliance bladder is caused by long-term BOO.Its phenomenon can be a smaller volume increase during the urinary storage period，which can produce a higher internal bladder pressure.In this experiment，nine rats in the experimental group had low-compliance bladders.Compared with the high-compliance bladders and the control group，there were statistically significant differences（P＜ 0.05）.With continued lower urinary tract obstruction，the increase of collagen fibers causes changes in bladder function and structure，extensive fibrosis of detrusor，and fewer elastic fibers，restricting the relaxing of detrusor cells，and causing bladder contracture.A small amount of volume change by filling can cause higher pressure in the bladder and the lower BC.

Conflicts of interest

All contributing authors declare no conflicts of interest.

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How to cite this article：Zhang H-Y，Ji H-X，Li W，et al.Correlation between bladder compliance and the content of detrusor collagen fibers.Chin Nurs Res.2016；3：83-85.http：//dx.doi.org/ 10.1016/j.cnre.2016.01.003

*Corresponding author.

E-mail address：zhy91225@126.com（J.-H.Zhang）.

Peer review under responsibility of Shanxi Medical Periodical Press.