GLOMERULAR PERMEABILITY TO PROTEINS - EFFECTS OF HEMODYNAMIC FACTORS ON DISTRIBUTION OF ENDOGENOUS IMMUNOGLOBULIN-G AND EXOGENOUS CATALASE IN RAT GLOMERULUS

Abstract

The distribution of endogenous immunoglobulin G (IgG) and exogenous catalase was delineated in the rat glomerulus under normal and abnormal hemodynamic conditions. IgG was identified by an ultrastructural immunoperoxidase technique using antirat IgG Fab fragments conjugated to horseradish peroxidase; catalase was identified by a cytochemical reaction. When superficial glomeruli in anesthetized Munich-Wistar rats were rapidly fixed in situ by dripping glutaraldehyde onto the renal surface, IgG and catalase were largely confined to the glomerular capillary lumen, with only small amounts in the lamina rara interna immediately beneath the endothelial fenestrae, and none deeper in the basement membrane (GBM) or in the urinary space. If cortical tissue was subjected to routine immersion fixation, or if fixation was performed in situ after ligation of the renal artery, IgG and catalase were found throughout the GBM but not in the urinary space. If fixation was performed in situ after ligation of the renal artery and vein (or artery, vein and ureter), IgG and catalase were found in the GBM and in the urinary space. If blood flow was restored for 10 min after 5 min of occlusion of the renal artery and vein, the distribution of IgG and catalase returned to that seen during good blood flow, i.e., neither showed significant penetration beyond the endothelial layer. Thus, as was found previously for albumin, glomerular barrier function for IgG and catalase depends upon the maintenance of normal blood flow conditions. Such conditions apparently impose functional restrictions to macromolecular penetration across the glomerular capillary wall. Such restrictions may be mediated by molecular sieving phenomena during normal ultrafiltration across the GBM, perhaps in association with concentration-polarization or charge effects or both. The epithelial slit pores may significantly modulate solute flux across the GBM by controlling the over-all rate of hydrodynamic flow during ultrafiltration.