Hyperplasia in the rabbit bladder urothelium following partial outlet obstruction. Autoradiographic evidence

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Abstract
Previous experiments have shown that adult male rabbits subjected to partial outlet obstruction or overdistension and acutely labeled, 24 h later,in vivo orin vitro with3H-Thymidine(3H-TdR) show high levels of incorporated radioactivity in bladder epithelium when they are visualized with autoradiography. To test the hypothesis that such labeling represents the onset of a wave of proliferation (that is, true hyperplasia), we injected3H-TdR subcutaneously in two normal and three partially obstructed New Zealand White male rabbits on each of days One, Two or Three following obstruction. Bladders were excised on the seventh day(D) following obstruction or the sixth day after injection of normals. Under these conditions, cells labeled with3H-TdR had the opportunity to proliferate, after labelling, for6(OneD and Normals),5(TwoD) or4(ThreeD) days respectively. After processing tissues for autoradiography, normal bladders showed only trace levels of labeling. Animals exposed to3H-TdR one day after obstruction, when large numbers of basal cells of the urothelium are known to incorporate3HTdR (i.e., synthesize DNA), showed labeling in most layers of the urothelium seven days after injection, but levels of labeling in bladders injected TwoD or ThreeD were lower than those injected OneD after obstruction. The smaller numbers of urothelial cells labeled by3H-TdR in TwoD bladders were found in clusters where one or two alternate or adjacent layers of cells were labeled. Obstructed animals injected ThreeD after surgery showed even less labeling. This evidence clearly supports the hypothesis that DNA synthesis that occurs in the urothelium within 24 h after obstruction is followed by proliferation, because by the seventh day, labeling can be found at all levels of the urothelium. The decline of labeling in TwoD and ThreeD animals suggests that the proliferative stimulus probably operates only during the first 24 h after insult. The data suggest that a substantial fraction of the urothelium enters one or more rounds of proliferation following obstruction and support the contention that hyperplasia does occur.