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

Outlet obstruction of the ratbladder induces hypertrophy/hyperplasiacharacterized by increases in bladder mass,smooth muscle content, and collagen deposition.In order to understand the mechanism of theoutlet obstruction-induced hypertrophy andhyperplasia, we first determined the temporalpattern of changes in bladder mass afterinducing the outlet obstruction. Histologicalanalysis revealed that the smooth muscle cellswith hypertrophy and hyperplasia, fibroblastsand connective tissue were increased in atime-dependent manner, corresponding to thetemporal pattern observed in the changes inbladder mass, although the phase of changes inthese tissue components was somewhat different.In order to further determine whether anyproliferation-stimulatory factors were releasedfrom the bladder with obstruction incorrespondence with increased bladder mass,soluble fractions were prepared from thebladders with outlet obstruction for 3–30weeks, and their effects on proliferation ofsmooth muscle cells were examined. The solublefractions prepared from the bladders at 3 to 14weeks after obstruction slightly butsignificantly facilitated the proliferation ofcultured smooth muscle cells, while the solublefractions released after 20 weeks rathersuppressed the proliferation. These resultssuggest that the initial increase in bladdermass might be in part due to the facilitatedproliferation of smooth muscle cells of thebladder body induced by growth factors releasedinto the soluble fractions, and thathypertrophy might then play a role in theincreased bladder mass at later phases.