Effect of gentamicin on glomerular ultrastructure.

Previous micropuncture experiments have shown that gentamicin reduces the glomerular Kf even at low doses. Light and transmission electron microscopy have failed to provide evidence of structural alterations to explain the observed decreases in Kf. To elucidate and effects of gentamicin on glomerular ultrastructure, we used both scanning and transmission electron microscopy to study the glomeruli of rats given gentamicin at 4 and 40 mg/kg/day for 10 days, as well as 20 mg/kg/day for 4 weeks. Observations were also made during recovery from gentamicin-induced renal injury. Scanning and transmission electron microscopy revealed that gentamicin induced striking reductions in endothelial fenestral diameter, density, and area. These changes were not appreciated by light microscopy. By quantitative measurements, the reductions in endothelial fenestral area were found to be parallel to the previously observed reduction in Kf. During recovery, the morphological alterations improved pari passu with functional recovery. Contrary to observations in other models of acute renal failure, gentamicin-induced glomerular injury was unique in that the visceral epithelial surface was not affected. The mechanisms by which gentamicin induces alterations in glomerular ultrastructure remain to be defined.