E. Johnsson et al., REDUCED PERMSELECTIVITY IN ISOLATED-PERFUSED RAT KIDNEYS FOLLOWING SMALL ELEVATIONS OF GLOMERULAR CAPILLARY-PRESSURE, Acta Physiologica Scandinavica, 150(2), 1994, pp. 201-209
A modified rat kidney preparation was used to explore how changes in h
ydrostatic pressure affect the permselective properties of the glomeru
lar capillary bed. The maximally vasodilated kidneys of 18 rats were p
erfused with albumin solutions (16.7 g l(-1)) at different flow rates
and hence arterial pressures (P-A). One kidney in each rat was exposed
to pressure elevations with the other kidney serving as a control per
fused at constant P-A of about 100 mmHg. Both the vascular resistance
to flow and the glomerular filtration rate (GFR 34.6+/-2.9 ml min(-1)
100 g(-1)) were similar in the two kidneys at equal P-A and remained c
onstant throughout the experiment. The ratio of albumin clearance over
GFR (Theta) was initially around 0.40% at constant P-A and gradually
increased during 1.5 h to reach 0.7% at the end of the experiment. A d
irect increase of P-A from 100 to 200 mmHg for 15 min resulted in a ca
lculated increase of the effective glomerular filtration pressure grad
ient of 10-15 mmHg and in a two-fold increase of Theta when measured a
t an identical P-A of 100 mmHg. Albumin clearance was almost fully nor
malized within 20 min similar to that observed in e.g. skeletal muscle
. However, the glomerular capillary barrier seemed to be far more sens
itive to elevations of hydrostatic pressure than other capillary walls
which require capillary pressure increments of 60 mmHg in order to in
duce similar reversible changes in permeability. Therefore, we conclud
e that an elevated P-GC per se induces changes of glomerular permselec
tivity, which map have important pathophysiological implications durin
g conditions of proteinuria.