Changes in the molecular sieve of the glomerular basement membrane of rats with chronic serum sickness.

In order to explore the pathogenic mechanism of proteinuria in glomerulonephritis, ultrastructural changes of the glomerular basement membrane were investigated in rats with chronic serum sickness induced by repeated intravenous injections of bovine serum albumin (experimental rats). Rats injected with saline served as controls. The animals were sacrificed and examined 13 weeks after treatment, when the mean urinary protein of experimental animals reached 206 mg/24h/100g body weight. Enhanced transcapillary passage of anionic ferritin was observed in experimental rats. Purified glomerular basement membranes of control and experimental rats were examined by electron microscopy after negative staining. The glomerular basement membrane of experimental rats had enlarged pores. The results suggest that an increase in the radius of glomerular pores may be responsible for proteinuria in glomerulonephritis.