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

Purpose: We test the hypothesis that oxybutynin chloride inhibits bladder s mooth 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 count ing cell numbers 48 and 96 hours after plating. To investigate the role of oxybutynin in bladder smooth muscle cell proliferation after mechanical str etch, cells were grown on silicone elastomer bottomed culture plates and su bjected to cyclical stretch-relaxation for 48 hours in the presence of 10 m u M. oxybutynin. Deoxyribonucleic acid synthesis was assessed by tritiated thymidine incorporation assay. To examine the effect of oxybutynin on stret ch activated gene expression, bladder smooth muscle cells were subjected to stretch-relaxation for 2 hours with and without 10 mu M. oxybutynin, and r elative c-jun messenger (m) ribonucleic acid (RNA) levels were assessed by semiquantitative reverse transcriptase-polymerase chain reaction with norma lization 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 synthes is after mechanical stretch, which decreased by 40% (p <0.01) when cells we re stretched in the presence of oxybutynin. Stretch stimulated significant increase in c-jun mNRA levels, which was significantly decreased by oxybuty nin. Conclusions: Oxybutynin chloride inhibits bladder smooth muscle cell prolif eration induced by serum and mechanical stretch. A potential mechanism by w hich 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 decre asing intravesical pressure.