Oxybutynin chloride inhibits proliferation and suppresses gene expression in bladder smooth muscle cells

Purpose: We test the hypothesis that oxybutynin chloride inhibits bladder smooth muscle cell proliferation. Materials and Methods: Cultured rat bladder smooth muscle cells were grown in Medium 199* supplemented with 10% fetal bovine serum in the presence of 0, 1, 10 and 100 mu M. oxybutynin. Cell proliferation was assessed by counting cell numbers 48 and 96 hours after plating. To investigate the role of oxybutynin in bladder smooth muscle cell proliferation after mechanical stretch, cells were grown on silicone elastomer bottomed culture plates and subjected to cyclical stretch-relaxation for 48 hours in the presence of 10 mu M. oxybutynin. Deoxyribonucleic acid synthesis was assessed by tritiated thymidine incorporation assay. To examine the effect of oxybutynin on stretch activated gene expression, bladder smooth muscle cells were subjected to stretch-relaxation for 2 hours with and without 10 mu M. oxybutynin, and relative c-jun messenger (m) ribonucleic acid (RNA) levels were assessed by semiquantitative reverse transcriptase-polymerase chain reaction with normalization to glyceraldehyde-3-phosphate dehydrogenase mRNA levels. Results: The serum stimulated increase in bladder smooth muscle cell growth was inhibited by oxybutynin in a dose dependent manner. In bladder smooth muscle cells there was a 4.7-fold increase in deoxyribonucleic acid synthesis after mechanical stretch, which decreased by 40% (p <0.01) when cells were stretched in the presence of oxybutynin. Stretch stimulated significant increase in c-jun mNRA levels, which was significantly decreased by oxybutynin. Conclusions: Oxybutynin chloride inhibits bladder smooth muscle cell proliferation induced by serum and mechanical stretch. A potential mechanism by which oxybutynin inhibits proliferation may be the down regulation of growth promoting genes, such as c-jun. We speculate that oxybutynin may be useful for preventing permanent hypertrophic bladder changes in addition to decreasing intravesical pressure.