Partial outlet obstruction of the rat bladder induces a stimulatory response on proliferation of the bladder smooth muscle cells.

Outlet obstruction of the rat bladder induces hypertrophy/hyperplasia characterized by increases in bladder mass, smooth muscle content, and collagen deposition. In order to understand the mechanism of the outlet obstruction-induced hypertrophy and hyperplasia, we first determined the temporal pattern of changes in bladder mass after inducing the outlet obstruction. Histological analysis revealed that the smooth muscle cells with hypertrophy and hyperplasia, fibroblasts and connective tissue were increased in a time-dependent manner, corresponding to the temporal pattern observed in the changes in bladder mass, although the phase of changes in these tissue components was somewhat different. In order to further determine whether any proliferation-stimulatory factors were released from the bladder with obstruction in correspondence with increased bladder mass, soluble fractions were prepared from the bladders with outlet obstruction for 3-30 weeks, and their effects on proliferation of smooth muscle cells were examined. The soluble fractions prepared from the bladders at 3 to 14 weeks after obstruction slightly but significantly facilitated the proliferation of cultured smooth muscle cells, while the soluble fractions released after 20 weeks rather suppressed the proliferation. These results suggest that the initial increase in bladder mass might be in part due to the facilitated proliferation of smooth muscle cells of the bladder body induced by growth factors released into the soluble fractions, and that hypertrophy might then play a role in the increased bladder mass at later phases.