Persistence of inert macromolecules (imposil) in the rat mesangium and glomerular functional disturbance

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Abstract
Imposil iron—dextran is an inert tracer that has been used to study mesangial uptake and clearance of macromolecular material from the glomerular circulation. Such a tracer may be a useful marker of altered mesangial function in animals with some forms of glomerulonephritis. We have studied mesangial handling of intravenously injected Imposil (50 mg/100 g body weight) in normal rats by light, immunofluorescence and electron microscopy for up to 3 months. Mesangial cell uptake was maximal at 48–54 h. Extrusion and drainage of tracer to the vascular pole and distal tubule was evident at 3 days but iron was still present in mesangial cells at 3 months. Possible functional renal impairment resulting from persistent mesangially sequestered tracer was examined by measuring daily urine protein and iron excretion. A possible relationship between failure of mesangial cells to eliminate inert tracer and increasing glomerular permeability is demonstrated, suggesting that Imposil and similar inert macromolecules cannot be used for long‐term studies of mesangial function.

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