Study On The Roles Of ATP In Bladder Detrusor Instability In Rats

Backgrounds and objective:Detrusor instability(DI) is one of the most common bladder functional disorder in urology cilinical practices.In recent years,great progress has been achieved on nerve regulation,constructional and functional changes of detrusor smooth muscle.However,since the mechanisms of DI are very complex,either the neurogenic or the myogenic theory can not explain the occurrence of DI completely.The cholinergic nerve supersensitivity was thought as the most important mechanisms of DI. However,the effect of anti-cholinergic is not satisfactory in clinic.Such phenomenon indicates the existence of non-cholinergic factors in DI,among them the purinergic contraction evocked by adenosine triphosphate(ATP) and myogenic contraction are regarded mostly.Being the main manifestation of DI detrusor is the abnormality of contraction and excitability,so to investigate the effects of ATP on the detrusor contraction and activity will be benefit for understanding the role of ATP in DI.However,previous studies on it are rare and controversial.In bladder,the neurotransmitter ATP is released by bladder urothelial cells and nerves which controlling the detrusor.The objective of this study is to explore the roles of ATP in the occurrence of DI and hope to provide new theoretical supporting and strategy for the therapy of DI.Materials and methods:①The model of bladder outlet obstruction(BOO) was achieved by partially ligating the urethras of female,4～5 months old Sprague-Dawleys(SD) rats.The pseudo-operationed normal SD rats served as the control group.Six weeks after operation,the rats were divided into BOO DI group,BOO detrusor stability(DS) group and normal DS group according to conscious cystometry.②The effects of pyridoxalphosphate-6-azopheny1-2'4'- disulfonic(PPADS) and ATP on detrusor strips under electrical stimulation in each group were recorded.③The effects of PPADS and ATP on whole bladder was recorded by cystometry in vivo and in vitro.Results:①DI and DS model rats were established successfully.There were 70.59% (18+18/25+26) obstructed rats developed DI.②In the in vitro study,under the blockage of PPADS,the detrusor strip contraction strength were different among the three groups(BOO DI＞BOO DS＞normal DS,P＜0.05),but after adjustment by the weight of detrusor strips,there was no statistically different any more.③The spontaneous contraction frequencies in BOO DI group were higher than that of BOO DS and normal DS group,and there were no difference between the latter two groups.The spontaneous contraction strength were higher in BOO DI and BOO DS group than normal DS group, with no obvious difference between the BOO DI and BOO DS group.④The transient contraction and then long time diastole effect was recorded on detrusor smooth muscle strips in vitro originated by ATP,the higher ATP concentration,the higher the strengthened. It was more obvious in BOO DI group than the other two groups.ATP did not affect the spontaneous contractile frequency of detrusor strips.However,the spontaneous contractile amplitude was decreased by diastole effect of ATP.and vanished completely by 1 mmol/L ATP.There was no conspicuous difference in the decreased absolute value of the spontaneous contractile amplitude among the three groups under 100μmol/L ATP.⑤In vivo,PPADS increased bladder functional capacity,prolonged the interval-voiding time in both BOO DI and normal DS rat group,and ATP decreased the bladder functional capacity, shortened the interval-voiding time of urine in both groups.PPADS decreased the bladder unstable contraction frequency of DI group rats.70%of the normal DS rats were induced DI by ATP,especially high concentration of ATP.There were no obvious difference of the maximum bladder pressure of miction existed between the two groups.⑥In vitro,for the bladder pressure curve and bladder pressure at different time point,there were no significant difference in BOO DI and normal DS group rats when ATP and PPADS were given into the two group rat bladders respectively.But there was an obvious bladder contraction when ATP was added into the incubation solutions.The bladder contraction amplitude was decreased dramatically when the bladder was incubated previously with PPADS.There were no statistical difference in bladder pressure of the two groups at time points of 50 second,4 and 8 minute.Conclusions:①The improvement of detrusor spontaneous excitability may be one of the reasons which induce DI.②ATP can not affect detrusor spontaneous excitability. The increased purinegic contractile element in detrusor smooth muscle caused by ATP may be one of the reasons which cause DI.The supersensitivity of BOO DI detrusor to ATP leads to the purine contractile element to improve.③ATP released by the bladder urothelial cells can induce DI through nervous reflex.Probably,it is another mechanism of DI.