Structural changes in the diabetic kidney.

Diabetic glomerulopathy is characterized by a very slow development of basement membrane (BM) accumulation, manifested as thickening of the peripheral BM and increased volume of the mesangial BM-like material (BMLM) with mesangial expansion. The initiation of the process is probably at the onset of diabetes since the BM thickening is detectable after a few years. The BM accumulations at the two sites (PBM and BMLM) in the glomerular tuft are considered as two different expressions of a fundamental BM abnormality. The two locations present different conditions for quantitation, may have a different biochemical make-up, and immediate functional implications of the abnormalities may differ as well. In the long run, however, the two in concert lead to the ultimate solidification of the glomerular tuft with loss of capillary surface. The end-stage is glomerular closure, with elimination of glomerular function. A very close correlation has been found between the total remnant surface area of the glomerular capillaries and the level of GFR. Along with the classical changes of the diabetic glomerulopathy, changes in glomerular size are detectable. In early diabetes during the stages of glomerular hyperfunction, hypertrophy develops acutely at the onset of diabetes, leading to an increase in capillary surface corresponding to the increase in filtration rate. In the advanced stages when glomerular closure involves a proportion of the nephrons compensatory hypertrophy develops, thereby probably helping to preserve capillary surface for a period of time. The exact mechanisms that may influence these developments are not known, but underlying them all are the metabolic abnormalities of diabetes.