The glomerular polyanion (GPA) of the rat kidney II. GPA loss in vitro by a vasoactive serum fraction.

Fractions from normal rat serum were prepared using gel filtration techniques and tested for their capacity to affect glomerular polyanion (GPA) of normal rat kidney tissue in vitro after incubation for 2 h and 37 degrees with cryostat kidney sections. Subsequently these sections, incubated with serum fractions or neuraminidase solutions, were rinsed with aquadest and stained for sialoprotein using the colloidal-iron method, and evaluated for their stainability of GPA using light microscopy. GPA stainability of these sections was compared with the stainability of GPA of kidney sections from nephrotic rats. The same serum fractions were also tested for their capacity to induce increased vascular permeability in the rat skin in vivo using a standard vascular permeability tests. The results show that a fraction with an estimated mol. wt between 50 and 100 kilodaltons did affect GPA in vitro in a dose-related manner, whereas this fraction also induced increased dose-related vascular skin responses after intradermal injection into rats in contrast to control fractions. Such a vasoactive serum fraction which is able to affect an important part of the glomerular filter barrier in vivo might play a role in conditions of increased glomerular permeability.