Differentiation of glomerular filter and tubular reabsorption apparatus during foetal development of the rat kidney.

Differentiation of the glomerulus and the proximal tubule was studied in the rat foetus, especially with regard to the development of the protein filtration-reabsorption apparatus. Filtration starts several days before full differentiation of the glomerulus, when the glomerular basement membrane consists of a thin lamina alongside the podocyte membrane. Endocytosis is functional fom this time but fusion between endocytic vesicles and lysosome-like bodies occurs 2 days later. Foetal urine electrophoresis shows the presence of many proteins, including high molecular weight one, this proteinuria seeming chiefly due to the immaturity of the glomerular barrier.