Role of fibrinogen in the glomerular permeability of the perfused, isolated dog kidney

Glomerular permselectivity is dependent on adequate serum concentrations of orosomucoid

Orosomucoid, or alpha 1-acid glycoprotein, a serum protein known to be an "acute phase reactant" has recently been shown to be needed for the maintenance of normal capillary permeability in skeletal muscle and mesentery. Therefore, we were interested in studying whether the glomerular capillary wall is affected by orosomucoid as well. For this purpose, left and right kidneys from nine rats (group A) were isolated and perfused in situ and in parallel using separate solutions of human albumin (1.8% in Tyrode), differing in their content of orosomucoid, one containing 0.21 g/liter, the other less than 0.005 g/liter. The temperature was kept at 8 degrees C in order to minimize tubular reabsorption of fluid and albumin. The two kidneys showed identical and stable vascular resistances during the experiments. Also the glomerular filtration rates (GFR) were stable between 30 and 33 ml/min/100 g kidney. Initially, the two kidneys showed similar fractional albumin clearance (theta) values of approximately 0.003. However, in the "absence" of orosomucoid theta increased to become four- to fivefold higher in the test kidney than in the control kidney at the end of the 1 1/2 hour experiment. This difference was observed in all rats, suggesting that orosomucoid is needed also for the maintenance of the glomerular permselectivity. In a separate group of eight animals (group B), orosomucoid-containing albumin solutions were used in parallel with horse serum solutions to perfuse the two kidneys of each rat, at 8 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

The anionic matrix at the rat glomerular endothelial surface

The anionic macromolecules at the glomerular endothelial cell surface are visualized only when stained with cationic stains. We investigated the arrangement and composition of this anionic matrix at the luminal surface. Rat kidneys were perfused with anionic ferritin (pI 4.5), ferritin (pI 7.4), or cationized ferritin (CF, pI 8.3). Anionic ferritin (pI 4.5) did not bind to the capillary wall, ferritin (pI 7.4) bound discontinuously only to the laminae rarae of the basement membrane, but cationized ferritin (CF, pI 8.3) bound as a thick continuous layer to the cell plasmalemma and bound to the anionic matrix in the fenestral spaces. These observations show that an anionic matrix lines the entire capillary lumen surface, fills the fenestrae, and is interposed between the blood and the basement membrane at the fenestrae. The anionic constituents at the capillary luminal surface were identified by in vivo digestion with specific enzymes. Absence of CF binding following digestion with specific enzymes was taken to indicate the presence of the particular glycoprotein known to be susceptible to the enzyme used. Neuraminidase digestion revealed that anionic sites over the surface plasmalemma are mainly from sialoproteins. In contrast, the matrix in fenestral channels contains heparan sulfate, hyaluronic acid, and sialoproteins. Papain digestion showed no glycolipids at the luminal surface. The functions of this continuous anionic layer located at the luminal surface of glomerular capillaries have not yet been established.