Glomerular selective permeability to macromolecular neutral dextrans in experimental diabetes

Rats with streptozotocin-induced chronic diabetes mellitus develop a glomerulopathy functionally manifested by proteinuria. The ability of the glomerular capillary wall to retard filtration of macromolecules was examined in 5 chronically diabetic Munich-Wistar rats exhibiting excessive proteinuria (39 +/- 7 mg/24 h, mean +/- SEM) and 5 age-matched normal Munich-Wistar rats without increased proteinuria (4.7 +/- 0.2 mg/24 h). Urinary albumin excretion was not increased in the diabetic rats (2.0 +/- 0.6 mg/24 h vs 1.6 +/- 0.3 mg/24 h) suggesting that the normal net electronegative charge of the glomerular capillary wall was not altered. Fractional clearances of macromolecular neutral dextrans were similar in diabetic and normal rats throughout a wide range of molecular size (18-42 A). Glomerular filtration rate was the same in the two groups of rats (2.77 +/- 0.16 ml/min in diabetics and 2.72 +/- 0.11 ml/min in normals) suggesting that renal haemodynamic factors did not influence fractional clearances of neutral dextrans in diabetic rats. We conclude that the proteinuria exhibited by these chronically diabetic rats is not attributable to alterations of size-selective properties of the glomerular capillary wall, such as increases in the size or the number of pores.