The glomerular mesangium: kinetics using radiolabeled ferritin and the effects of aggregated IgG.

A quantitative method for studying glomerular mesangial kinetics using radiolabeled native ferritin (125I-NF) is described. Groups of Sprague-Dawley rats were given injections of monomeric 125I-NF in a dose of 10 mg/100 g and sacrificed at 4, 16, and 36 hr. Radioactivity was measured in preparations of isolated glomeruli, spleen, and liver, and in blood. After initial uptake, a progressive decrease in the concentration of 125I-NF was observed in the mesangium and other organs. To examine the effect of one macromolecule on the mesangial kinetics of NF a separate group of animals was given aggregated human IgG (AHIgG) (40 mg/100 g) 4 hr prior to administration of 125I-NF. The administration of AHIgG did not alter the kinetics of 125I-NF in the mesangium, plasma, or spleen but the disappearance of 125I-NF from the liver was accelerated. Although the cellular mechanisms for uptake of NF and AHIgG are different, the presence of one macromolecule (AHIgG) within the mesangium did not affect the uptake and disappearance of another (NF). Thus, the glomerular mesangium has a relatively high capacity under normal circumstances.