The concentration of albumin was measured by a double-antibody radioimmunoassay in the glomerular basement membrane (GBM) and tubular basement membrane (TBM) of patients with diabetic nephropathy, other kidney diseases, and normal kidneys. The TBM from diabetics contained significantly more albumin (m ± SD; 2.75 ± 0.34 μg/mg) than the TBM from other diseases (1.00 ± 0.24 μg/mg) or normals (1.21 ± 0.26 μ/mg) (P < 0.0001). Similarly, diabetic GBM contained more albumin (2.25 ± 0.59 μg/mg) than other diseases (1.22 ± 0.55) or normals (1.31 ± 0.36 μg/mg) (P < 0.01–0.001). No differences were observed between the normal and other disease groups. Although there were no differences in hydroxyproline content, there was a highly significant correlation between the concentration of hydroxyproline and albumin in the diabetic TBM (r = 0.82), diabetic GBM (r = 0.70), and normal TBM (r = 0.79). Elution studies with different buffers on frozen sections of diabetic kidneys suggest that the albumin is relatively firmly bound. Although albumin is present in extracellular membranes of normal and diseased human kidneys, the concentration is higher in diabetes mellitus.

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