Inside-out標本を用いた膀胱粘膜の水吸収機構の検討

抄録

Aims: It has been suggested that the urinary bladder has a physiological role for absorbing water, but there were few studies published. In contrast, the bladder mucosa plays the role of a barrier mechanism that does not allow urine to penetrate. In this study, we aimed to investigate mucosal permeability of rat urinary bladder by using newly established bladder “inside-out” preparation. 

Methods: Female adult Sprague-Dawley rats were used. Using isoflurane anesthesia rats were sacrificed and whole bladder was isolated. This whole bladder was used as normal (N=12) and inside-out (N=11) samples, and inside-out sample was reversed the bladder from the bladder top. For monitoring of intravesical pressure and instillation of Krebs solution, a catheter (PE-50) was inserted through the urethra and fixed with surgical suture at the bladder neck. The bladder was fixed vertically in a 30 ml organ bath with Krebs solution gassed with 5% CO₂ and 95% O₂ at 37℃. The bladder was instilled with Krebs solution at a rate of 6 ml/h. until the intravesical pressure reached 30 cmH₂O. The bladder was kept under an isovolumetric condition and allowed to stabilize for 5 min (approximately around 15-20 cmH₂O), and then high K⁺ (KCl: 50 mM) and acetylcholine (ACh: 10 μM) were added into the organ bath, and the intravesical pressure was recorded.

Results: In the normal bladder samples, intravesical pressure was remarkably increased with KCl (42.4 ± 3.3 cmH₂O) and ACh (33.3 ± 1.9 cmH₂O). In contrast in the inside-out bladder samples, the intravesical pressure was only slightly increased with KCl (1.0 ± 0.3 cmH₂O) and ACh (1.8 ± 0.2 cmH₂O). 

Conclusions: Bladder normal samples showed remarkable increased responses of the intravesical pressure to KCl and ACh, but inside-out samples did not show such responses. The present study revealed that the bladder detrusor smooth muscle potentially has water (urine) permeability, whereas bladder mucosa has robust barrier mechanisms for preventing absorb water (urine) in at least normal rat.