Homeostatic efficiency of tubuloglomerular feedback is reduced in
established diabetes mellitus in rats.
Vallon, Volker, Roland C. Blantz, and Scott Thomson.
Division of Nephrology-Hypertension, Dept. of Medicine, University
of California San Diego and San Diego Veterans Administration Medical
Center, San Diego, California 92161
APStracts 2:0098F, 1995.
We tested the hypothesis that the ability of the tubuloglomerular
feedback (TGF) to stabilize renal function is impaired in rats with
7-8 weeks of insulin-treated streptozotocin-diabetes. Proximal
tubular flow was measured in free-flowing nephrons using a non
-invasive optical technique. The homeostatic efficiency of TGF was
determined from the fractional compensation (C) for perturbations in
ambient flow. C was substantially reduced in diabetic rats. To assess
the roles of the proximal tubule and loop of Henle as determinants of
TGF efficiency, we tested the effect of diabetes on proximal tubular
reabsorption as determined by standard micropuncture and on the ionic
content of early distal tubular fluid by employing a microelec trode
for on-line measurement of electrical conductivity (TED). Diabetes
caused glomerular hyperfiltration and increased fractional proximal
tubular reabsorption (FPR), such that late proximal (VLP) and early
distal tubular flow were unaffected. The increase in FPR was a minor
contributor to the overall effect on C. Diabetes decreased the
ambient TED without affecting the slope of the relationship between
VLP and TED. These results demonstrate that the homeostatic
efficiency of the TGF system is reduced in diabetes and that this
cannot be fully accounted for by changes in tubular reabsorption.
Impaired TGF efficiency renders the diabetic glomerular
microvasculature more susceptible to impact from fluctuations in
systemic hemodynamics.
Received 24 March 1995; accepted in final form 6 June 1995.
APS Manuscript Number F102-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.