Functional characteristics of the glomerular filter in the IgA-nephropathy

The purpose of the present study was to compare the functional characteristics of the glomerular filter in patients having a well defined glomerulonephritis, the IgA nephropathy, with those of normal age-matched controls. A bolus intravenous injection of inulin (60 mg/kg), para-amino hippuric acid (36 mg/kg) and Rheomacrodex (130 mg/kg) was administered to each subject and followed by the timed collection of venous blood and urine samples. Compared to the controls, the nine patients with IgA nephropathy had no significant differences in renal plasma flow or glomerular filtration rate. The control group showed filtration of the neutral graded dextrans which diminished in a linear fashion with increasing molecular size. In contrast, the IgA patients showed two-phased glomerular sieving with a reduction in the filtration of dextrans sized 40 A or less and an increased filtration of those larger than 50 A. These changes in dextran filtration indicate the appearance of a population of larger than normal pores in the glomerular filter in the IgA nephropathy, although concomitant alterations in the electrostatic properties of the filter mechanism cannot be excluded.