The permeability of glomerular capillaries of aminonuceoside nephrotic rats to graded dextrans.

Abstract

We have recently used graded dextrans as tracers to investigate glomerular permeability in normal rats (1) in order to determine which structure in the glomerular capillary wall, the basement membrane or the epithelial slits, represents the primary filtration barrier to macromolecules . Three dextran fractions of specified mol wt (40,000, 62,000, and 125,000) were prepared which bracket the size of albumin, the molecule effectively retained by the normal glomerulus. When injected intravenously into rats, the dextran fractions behaved as predicted in that they were extensively filtered, filtered in small amounts, and extensively retained, respectively . In all three cases dextran particles were found initially in high concentration in the capillary lumen and in the subendothelial portions of the basement membrane but there was a sharp drop in their concentration at this level, i.e., between the inner looser portions of the basement membrane and its outer more compact portions . With the two largest fractions accumulation of particles occurred against the basement membrane in mesangial regions with time, but no accumulation was ever seen with any of the fractions in the epithelial slits or against the slit membranes . Therefore, we concluded that the results obtained with dextrans, like those obtained previously using ferritin as a tracer (2, 3), identify the glomerular basement membrane as the main barrier to the passage of macromolecules of the size of albumin in the normal glomerulus.In order to extend these observations we have carried out similar studies on animals with experimental nephrosis (induced with an aminonucleoside of puromycin) . Nephrotic animals represent an interesting situation in which to study glomerular permeability since they show albuminuria due to increased leakage of albumin by the glomerulus, accompanied by profound changes in the glomerular capillary wall (cf. 4) : the usual epithelial foot process organization is lost with a concomitant reduction in the number of epithelial filtration slits, the epithelial cells become filled with protein absorption droplets (i.e., phagosomes and lysosomes), and the basement membrane appears thinner and less compact in some regions.

Proteinuria and structural alterations in rat glomerular basement membranes induced by intravenously injected anti-laminin immunoglobulin G.

“…Proteinuria was probably not caused by complement either because there was no change in the amount of glomerular C3 detected subsequent to the acute period and because most proteinuric animals had no complement in their glomeruli. The reason for proteinuria, however, was most probably due to changes that occurred within the glomeruli because the epithelial cells had absorption droplets (31)(32)(33), microvilli formation (34), and displaced slit diaphragms (33,35), all of which are changes seen in other glomerular proteinurias.…”

“…Flocculent, subendothelial deposits were seen in the GBM 2 wk after the injection of SaL, and by 6 wk, focal areas of greatly increased width measuring as much as 1.5 #m (normal is 0.15 #m; ref. 20) were present in the peripheral capillary (Fig. 10 a).…”

“…SaT-HRP of the same concentration was injected into four additional animals. 1-2 h after injection, the left kidney of each animal was fixed in situ (20) with 1% formaldehyde and 3% glutaraldehyde in 0.1 M sodium cacodylate, pH 7.4 (21). Sections of cortex 40-~tm thick were incubat~ed in 0.05% diaminobenzidine (DAB) and 0.01% H202 (22), pH 6.0, washed in buffer, and post~fixed in 2% OsO4 in 0.1 M phosphate, pH 7.3.…”

Mechanisms of the Puromycin-Induced Defects in the Transglomerular Passage of Water and Macromolecules

“…Morphologically, PAN regularly leads to loss of organization of the normally slender and interdigitating glomerular epithelial cell foot processes, or pedicels. These pedicels are replaced instead, in some areas, by more or less continuous sheets of epithelial cytoplasm, while in other areas the urinary aspect of the glomerular capillary basement membrane (GBM) appears devoid of any epithelial cell covering (9)(10)(11)(12)(13)(14)(15)(16)(17). In addition, biochemical and ultrastructural alterations in the GBM (3,11,16) as well as in mesangium have been noted (4,8,16).…”

Effect of hemodynamic factors in renal glomerulus. I. Alterations of glomerular basement membrane in the experimental congestive kidney.

“…The basement membrane is divided into an electron dense central region (lamina densa) and electron lucent zones on each side (lamina rara interna and lamina rara externa) (2,6).…”