The glomerular ultrastructural distribution of immunoglobulin G in hyperalbuminaemic (protein-overload) proteinuria.

Female Munich-Wistar rats were given intraperitoneal injections either of bovine serum albumin to induce proteinuria or of water as a control. Their kidneys were fixed in situ. An ultrastructural technique was used to demonstrate IgG antiperoxidase antibodies either injected from a heterologous species or autologous, induced by immunization with horseradish peroxidase. Photometry of electron micrographic negative was used to determine the distribution of antiperoxidase antibodies. In glomeruli of control animals IgG was present in the basement membrane. There were three sites at which the passage of IgG across the basement membrane was hindered: between blood plasma and the lamina rara interna, between the lamina densa and the lamina rara externa, and between the lamina rara externa and the urinary space. Glomeruli of proteinuric animals were variable in appearance, some showing little structural damage and others showing marked changes with loss of epithelial foot processes and accumulation of vacuoles and protein droplets in epithelial cells. Both types of glomeruli contained IgG in the urinary space. The distribution of IgG in the basement membrane of both types was similar. Compared with control animals there was less IgG in the basement membrane and IgG was distributed uniformly across the basement membrane. The proteinuria in hyperalbuminaemia (protein-overload) is associated with a diffuse change in the barrier function of the glomerular basement membrane to IgG which is, at least in the initial stages, not related to structural changes in glomerular epithelial cells.