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.