Age-dependent thickening of glomerular basement membrane has no major effect on glomerular hydraulic conductivity.
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 (K(f)) 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 mm(2) in young and 0.244 mm(2) in old rats (P<0.0005). However, k was not significantly different (18.0 nl/s.mmHg.cm(2) in young and 15.8 nl/s.mmHg.cm(2) 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.
Neumann
Klaus H
KH
Klinik für Nephrologie, Universitätsklinikum, Leipziger Strasse 44, D-39120 Magdeburg, Germany. Klaus.Neumann@medizin.uni-magdeburg.de
Kellner
Christian
C
Kühn
Karlwilhelm
K
Stolte
Hilmar
H
Schurek
Hans-Joachim
HJ
D000367:Age Factors; D000818:Animals; D001485:Basement Membrane / Q000473:pathology; D055592:Biophysical Phenomena; D001703:Biophysics; D066298:In Vitro Techniques; D007678:Kidney Glomerulus / Q000033:anatomy & histology / Q000098:blood supply / Q000473:pathology* / Q000502:physiology*; D008297:Male; D008833:Microcirculation; D010477:Perfusion; D051381:Rats; D017208:Rats, Wistar