Nephrol Dial Transplant (2004) 19: 805-811
Nephrol Dial Transplant Vol. 19 No. 4 © ERA-EDTA 2004; all rights reserved
Original Article
Age-dependent thickening of glomerular basement membrane has no major effect on glomerular hydraulic conductivity
Klinik für Nephrologie, Universitätsklinikum Magdeburg and Abteilung für Nephrologie, Medizinische Hochschule Hannover, Germany
Correspondence and offprint requests to: Klaus H. Neumann, MD, Klinik für Nephrologie, Universitätsklinikum, Leipziger Strasse 44, D-39120 Magdeburg, Germany. Email: Klaus.Neumann{at}medizin.uni-magdeburg.de
Background. The effect of the increasing thickness of the glomerular basement membrane (GBM), which is seen in ageing rats, on the effective hydraulic conductivity (k) of the glomerular capillary wall was studied in Wistar rats aged 2 and 18 months.
Methods. With the use of micropuncture techniques, ultrafiltration characteristics of cortical glomeruli were determined in isolated cell-free perfused kidneys. Because the filtration fraction in this preparation is low (3%) as a consequence of high perfusion rates at glomerular filtration rates comparable with in vivo conditions, uniform ultrafiltration conditions are provided over the whole filtering surface. After fixation at a defined perfusion pressure, the surface of glomerular capillaries (S) was obtained morphometrically on light microscopic sections of the glomeruli studied previously.
Results. The glomerular ultrafiltration coefficient (Kf) was 0.025 nl/s·mmHg in young rats and 0.038 nl/s·mmHg in old rats (P<0.0005) and S was 0.140 mm2 in young and 0.244 mm2 in old rats (P<0.0005). However, k was not significantly different (18.0 nl/s·mmHg·cm2 in young and 15.8 nl/s·mmHg·cm2 in old rats) despite a 2.4-fold increase of GBM thickness as estimated from electron microscopic sections.
Conclusions. These findings indicate that the age-dependent increase of GBM thickness in rat kidneys did not substantially increase hydraulic resistance of the glomerular capillary wall.
Keywords: ageing rat kidney; glomerular capillary basement membrane thickness; glomerular capillary surface area; glomerular effective hydraulic conductivity; isolated perfused kidney; micropuncture methods
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