Changes of Detrusor Contractility after Partial Bladder Outlet Obstruction and Relief of Obstruction in Rat: Long-term Evaluation

ABSTRACT

PURPOSE: The contraction of the bladder is biphasic in nature consisting of an initial phasic contraction followed by a prolonged tonic contraction that is responsible for evacuating the bladder. Previous study demonstrated that the relief of bladder outlet obstruction induced recovery of the ability to initiate contraction, but emptying ability was not recovered within a certain period of time. This study was designed to determine the ability of recovery in tonic contraction and changes of contraction to pharmacologic stimulation through longterm evaluation after relief of obstruction. MATERIALS AND METHODS: Forty eight female rats were used in this investigation. Normal bladder was used as control and experimental groups were classified into 6 weeks obstruction group and 3, 6, 9, 12 weeks groups after relief of obstruction. The phasic and tonic contractile response to field stimulation(2, 4, 8, 16, 32Hz) and the response to bethanechol(3x10-5M), ATP(1mM) and KCl(120mM) were estimated by polygraph. RESULTS: The weight of bladder increased in obstruction group and gradually decreased after relief of obstruction. The phasic and tonic contractile response to all frequency of stimulation were decreased in obstruction group and recovered after relief of obstruction. In low frequency of stimulation, the ratio of tonic to phasic contractile response was decreased in obstruction group and recovered from 9 weeks after relief of obstruction. The contractile response to bethanechol was decreased in obstruction group and rapidly recovered after relief of obstruction. However, there were no change in contractile response to ATP in all group. The contractile response to KCl was decreased in obstruction group, but there were no change after relief of obstruction. CONCLUIONS These results indicate that the emptying ability is recovered slowly but not enough and the contractile response to cholinergic stimulation is rapidly recovered after relief of obstruction. Further study will be needed for response to ATP and KCl.