DU Is Induced by Low Levels of Urinary ATP in a Rat Model of Partial Bladder Outlet Obstruction: The Incidence of Both Events Decreases after Deobstruction

Abstract

Objectives: To investigate, in initial phases of bladder outlet obstruction (BOO), the urinary ATP levels, the incidence of detrusor underactivity (DU), and if they change after deobstruction.

Methods: Adult female Wistar rats submitted to partial BOO (pBOO) and sham-obstruction were used. Cystometry was performed 3 or 15 days after pBOO and fluid was collected from the urethra for ATP determination. Bladders were harvested for morphological evaluation of the urothelium. DU was defined as the average of voiding contractions (VC) of sham-operated animals, with 3 SD at 15 days after the sham surgery. In another group of animals in which pBOO was relieved at 15 days and bladders were let to recover for 15 days, the incidence of DU and ATP levels were also accessed. The Kruskal-Wallis test was followed by Dunn's multiple comparisons test, and Spearman's correlation test was used.

Results: DU was present in 13% and 67% of the bladders at 3 and 15 days after pBOO, respectively, and in 20% of the bladders at 15 days after deobstruction. ATP levels were significantly lower in DU/pBOO versus sham and non-DU/pBOO rats. A strong positive correlation between ATP levels and VC/min was obtained (r = 0.63). DU bladders had extensive areas in which umbrella cells appeared stretched, the width exceeding that presented by sham animals.

Conclusions: Low urothelial ATP parallels with a high incidence of DU early after pBOO.

Figure 1

Scatter-plot of ATP levels on saline voided by animals. Scatter-plot showing the value of ATP (mol/ml) in saline voided by each animal (symbols), as well as the mean value ± standard deviation of ATP (mol/l) in saline voided by normoactive animals (sham, •), animals with DU after obstruction (DU/pBOO, ■), and animals without DU after obstruction (non-DU/pBOO, ▴).

Figure 2

Spearman's correlation between log ([ATP] voided) levels and voiding frequency (VC/min). Scatter plot showing Spearman's correlation between the logarithm of the amount of saline-voided ATP and the voided contraction presented by each animal (•). All values on or below the horizontal dash line represent animals with the DU phenotype. The DU/pBOO and DU/rBOO animals all presented levels of saline-voided ATP inferior to 1.00E-16 (values on the left side of the dash line vertical line). VC, voiding contractions.

Figure 3

Typical cystometrograms of DU animals after stimulation with ACh and ATP. Images of a typical cystometrogram of one of the six animals that did not present bladder contraction (voided by overflow) and received (a) a topical application of 1 µM of ACh in the serosa. In this cystometrogram, the single application of ACh (red arrow) generated an immediate voiding contraction. (b) After washout, the same animal intravesical received 5 mg/kg of ATP (red arrow), resulting in voiding contractions.

Figure 4

Representative microphotographies of bladder urothelium. Representative microphotographies of bladder slides stained with H&E of (a) an animal with a normal phenotype and (b, c) of an animal with the DU phenotype. (a, c) Normal urothelial cell features. The microphotography (b), however, presents an extra-stretched urothelial cell configuration. Scale bar: 50 µm.