Intravesical pressure induces hyperplasia and hypertrophy of human bladder smooth muscle cells mediated by muscarinic receptors

Abstract 

Purpose

Bladder outlet obstruction with intravesical pressures exceeding 40cmH₂O results in a progressive increase in wall thickness, eventually causing low compliance. We investigated whether intravesical pressure induces hypertrophy and/or hyperplasia of human bladder smooth muscle cells (HBSMC) mediated by a muscarinic (M) receptor, and evaluated the relationship between intravesical pressure and M receptor antagonists.

Materials and methods

HBSMC were exposed to 40cmH₂O pressure and/or acetylcholine (10nM–100μM) for 24h. Cells exposed to hydrostatic pressure were treated with either 1μM AF-DX 16 (M₂ antagonist), 1μM 4-DAMP (M₃ antagonist) or 1μM atropine (both M₂ and M₃ antagonists). DNA and protein synthesis of HBSMC were measured by ³H-thymidine and leucine incorporation assays, respectively.

Results

³H-thymidine incorporation increased following exposure to increasing concentrations of acetylcholine (at 100μM, P<0.05). When cells were exposed to 40cmH₂O for 24h, ³H-thymidine incorporation increased by 31.4%, 33.3% and 39.5% in 1μM, 10μM and 100μM of acetylcholine, respectively. With exposure to 100μM acetylcholine, a hydrostatic pressure of 40cm, and both of these together, ³H-thymidine incorporation increased by 16.7%, 25.9% and 39.4%, respectively, and leucine incorporation increased by 66.5%, 66.5% and 81.8%, respectively (P<0.05). Antimuscarinic agents had no apparent effect on the proliferative rate of cells grown at atmospheric pressure, but there was a dramatic decrease in thymidine and leucine incorporation for cells that were simultaneously exposed to increased hydrostatic pressure, most pronounced when the combined M₂/M₃ receptor antagonist was applied.

Conclusions

Intravesical pressure may induce hypertrophy/hyperplasia of HBSMC mediated by M receptors. Early use of an M receptor antagonist in cases of high intravesical pressure may have a positive effect on bladder compliance.

Keywords: Muscarinic receptor, Bladder smooth muscle, Hyperplasia, Hypertrophy, Intravesical pressure