Effect of transient renal ischemia on papillary BrdU-retaining cells. The presence of BrdU-retaining cells was examined in papillae of control kidneys and of kidneys subjected to transient ischemia. (A) In 100-μm papillary sections 3 weeks after ischemia, compared with control, there was a marked decrease in BrdU-retaining cells in the papilla of the ischemic kidney. (B) Sections 5 μm in thickness showed that while the papillary tip of the control kidney had numerous BrdU-retaining cells, that of the ischemic kidney had very few. (C) For quantification of the effect of renal ischemia on the number of BrdU-retaining cells, 6 rats 5 months of age were subjected to transient ischemia of the left kidney; 3 weeks later their kidneys were harvested and cells from different parts of both kidneys were stained for BrdU and analyzed by flow cytometry. In all graphs, the y axis shows the number of cells, while the x axis (FL2-H) shows the fluorescent intensity. MI is the area of positive cells. In the papillae of the nonischemic kidneys, the number of BrdU-retaining cells averaged 36% of the total cells, while in the papillae of the kidneys subjected to transient ischemia, this number was only 4%, as shown to the left of each histogram. Compared with the control kidney, the ischemic kidney also had a slight decrease in the number of BrdU-positive cells in the medulla and cortex, suggesting that the papillary BrdU-retaining cells had not simply migrated to other parts of the kidney. Scale bars: 50 μm.