Muscarinic receptor expression increases following exposure to intravesical pressures of < or =40 cm-H2O: a possible mechanism for pressure-induced cell proliferation.

OBJECTIVE

We studied the effect of increased hydrostatic pressure on muscarinic (M) receptor expression in isolated human bladder smooth muscle cells (HBSMCs) and in an in vivo model of acute bladder outlet obstruction (BOO). We evaluated additionally whether acetylcholine functions as BSMCs mitogen.

METHODS

HBSMCs were exposed to sustained levels of increased hydrostatic pressure. Expression of the M2 and M3 receptors was measured by Western blot analysis. Acute BOO was maintained in five male pigs for 24 h; six normal animals served as controls. Expression of the M2 and M3 in tissues was evaluated in a similar fashion to the isolated cells. HBSMCs were subsequently exposed to 100 microM acetylcholine in the presence or absence of hydrostatic pressure. DNA and protein synthesis were measured using a 3H-tymidine and leucine incorporation assay, respectively.

RESULTS

Mean (range) detrusor pressure in acute BOO and controls was 19 (1-36.1) and 3.1 (1-16) cm-H2O, respectively. M2 and M3 receptor expression in HBSMCs increased in a time-dependent and pressure-dependent manner. Both M2 and M3 expressions in BOO model were markedly upregulated when compared to controls. Compared to controls, thymidine and leucine incorporation in HBSMCs demonstrated a significant increase following exposure to 100 microM acetylcholine and/or 40 cm-H2O.

CONCLUSIONS

M2 and M3 receptors are upregulated in a time-dependent and pressure-dependent fashion after as little as a 24 h exposure to increased hydrostatic pressure. Acetylcholine has a more profound proliferative effect when cells are simultaneously exposed to increased levels of hydrostatic pressure.