Rat kidneys undergoing tubular regeneration after ischaemic injury have been examined with regard to EGF, EGF receptor and vimentin, using immunohistochemical techniques. Renal ischaemia was induced in male Sprague-Dawley rats by 35-min clamping of renal arteries. Groups (n = 4-6) of experimental animals were killed at different time intervals (12, 24, 48, 72 h, 7 and 14 days) after reperfusion. One hour before sacrifice, each rat received i.p. 200 mg/kg 5-bromo-2'-deoxyuridine (BrdU) for the immunocytological demonstration of DNA synthesis. Renal necropsies were processed to reveal by immunohistochemistry EGF, EGF receptor, vimentin, and BrdU incorporated into DNA of S-phase cells. Tubular necrosis particularly involved proximal straight tubules in the outer stripe of the outer medulla and was followed by tubular regeneration, with a peak of cell proliferation at 48-72 h and an apparent dedifferentiation of tubular epithelium. As soon as 12 h after ischaemia, there was a substantial reduction of EGF immunostaining and the incidence of distal tubules showing EGF immunoreactivity reached a nadir at 48 h. In control kidneys, EGF receptor was mostly immunolocalized in proximal tubules although juxtaglomerular cells also exhibited immunolabelling. EGF receptor immunostaining in tubular epithelium showed no major change during the episode of tubular necrosis (12-24 h) but disappeared in tubular profiles undergoing regenerative hyperplasia (48-72 h). No vimentin immunostaining was found in tubules of control kidneys. Tubular epithelium remained mostly vimentin negative during the early phase of tubular necrosis/regeneration (12-72 h). By contrast, 7 days after ischaemia numerous dedifferentiated tubules expressed vimentin. In conclusion, tubular regeneration after ischaemia is associated with a typical sequence of transient events: (1) reduction of EGF immunostaining; (2) disappearance of EGF receptors during the mitogenic response; (3) expression of vimentin in tubular epithelium, and (4) return to a normal appearance.

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Immunocytological localization of epidermal growth factor in the rat kidney after drug-induced tubular injury.

The present study was undertaken to analyze, at the cytological level, the intrarenal distribution of epidermal growth factor (EGF) in normal conditions and after drug-induced tubular injury. Female Sprague-Dawley rats were injected with gentamicin (50 mg/kg.day) for 4 days to induce tubular necrosis and were terminated 4 days after the last drug administration. For light microscopy, EGF immunoreactivity was demonstrated by immunogold-silver staining. In the kidneys of control rats EGF was found associated with distal tubules (cortex and outer medulla). Kidney exposure to gentamicin resulted in a drastic decrease of EGF immunoreactivity. For the electron microscopy study, immunoreactive EGF was detected on ultrathin sections by immunogold labeling. Within distal tubules epithelium of control animals, immunoreactive material was predominantly seen on the basolateral membrane, and to a much lesser extent in the cytoplasm or on the apical membrane. After treatment with gentamicin, there was a reduction of the density of gold particles observed in distal tubule cells. Interestingly, gold particles also appeared, but at a lower density, in proximal tubule cells. In these cells, EGF immunoreactivity also seemed membrane-bound and was mostly observed on (or next to) the basolateral membrane.

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