This study examined the effects on proximal tubule morphology of blocking single nephrons with paraffin wax for one day, one week, or one month in the rat. Proximal tubule lumens were blocked with a short column of wax using micropuncture. Chronically blocked and control (normal) tubules were fixed by either intravascular or intraluminal perfusion of glutaraldehyde solution. Proximal tubule segments downstream to the wax block were examined by light and transmission electron microscopy. Intraluminal Alcian blue dye, serial sectioning, and nephron microdissection techniques were used to identify nephrons. One day after obstruction, all proximal tubule cells downstream to the block were injured. Some recovery was seen. S1 and S2 segments showed more severe damage than S3 segments. Alcian blue, which normally is excluded from cells, entered the cytoplasm of some damaged S1-S2 cells. After one week of obstruction, the tubule appeared to have reconstituted itself, but cells were less differentiated than normal. One month after obstruction, blocked tubules were atrophied. Tubule cells were simplified and were surrounded by a thickened basement membrane. The results suggest that prolonged proximal tubule blockade produces injury and atrophy of the proximal tubule probably due to ischemia and interruption of normal reabsorptive activity.
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