Effects of Relief of Bladder Outlet Obstruction on the Detrusor Contractility in Rat

Kim, Joon Chul; Yoon, Jai Young; Hwang, Tae Kon; Park, Yong Hyun

Abstract

Contraction of the bladder can be divided into two phases. The initial phase (phasic contraction) is characterized by a rapid increase in pressure that results in a change of bladder shape. This phase is followed immediately by a plateau phase (tonic contraction) that maintains an increase in intravesical pressure that is responsible for evacuating the bladder. This study was designed to determine the effect of relief of bladder outlet obstruction on the phasic and tonic detrusor contractile response to field and pharmacologic stimulation in rat urinary bladder. Forty female rats were used in this investigation. Normal bladder was used as control(n=8) and experimental groups (n=32) were classified into 6 weeks obstruction group and 2, 4, and 6 weeks groups after relief of obstruction. The phasic and tonic contractile response to field stimulation (2, 4, 8, 16, 32 Hz) and bethanechol (3 x -100,000 M) was estimated by polygraph. Following results were obtained. 1) The weight of bladder was increased in obstruction group and gradually decreased after relief of obstruction (p<0.05). 2) The phasic and tonic contractile response to all frequency of stimulation was decreased in obstruction group and rapidly recovered from 4 weeks after relief of obstruction (p<0.05). 3) In low frequency field stimulation, the ratio of tonic to phasic contractile response was decreased in obstruction group when compared with control (p<0.05) and in all frequency field stimulation, the ratio tended to recover after relief of obstruction (p>0.05). 4) Detrusor contractile response to bethanechol was rapidly decreased in obstruction group and rapidly recovered after relief of obstruction. And the contractile response in 6 weeks after relief of obstruction was higher than control (p<0.05). As the results of above, we concluded that relief of bladder outlet obstruction induced recovery of the ability to initiate contraction2 However, emptying ability is not recovered within a certain period of time. And further study will be needed.