Effect of dietary protein and enalapril on proximal tubular
delivery and absorption of albumin in nephrotic rats.
Fitzgibbon, Wayne R., Sarah K. Webster, Akiko Imamura, David W. Ploth,
and Florence N. Hutchison.
Division of Nephrology, Department of Medicine, Medical University
of South Carolina, Charleston, SC 29425 and the Ralph H. Johnson
Veterans Affairs Medical Center, Charleston, SC 29403
APStracts 3:0029F, 1996.
In passive Heymann nephritis (PHN), angiotensin-converting enzyme
inhibition (CEI) or a low dietary protein intake decreases
albuminuria (UAlbV). Although this reduction in albuminuria appears
to result from an improvement in glomerular permselectivity, the
effect of these treatments on albumin permeation and absorption by
the nephron has not been clarified. This study used micropuncture
techniques to examine effect of these 2 treatments on albumin
permeation (by measuring the delivery of albumin to the proximal
tubule) and the tubular absorption of albumin. PHN rats (12-18 days
after injection of FX1A) were switched from 21% to either 40% protein
diet (HP), 40% protein diet and concomitantly treated with enalapril
(40 mg/day) (HPE), or to 8% (LP) protein diet for 4-6 days. Although
left kidney GFR did not differ among the groups, UAlbV from the left
kidney in LP and HPE was only 20-40 % of that observed for the HP
group. In Protocol 1, the fractional recovery of albumin (FRAlb) in
urine was calculated following injection of artificial tubular fluid
containing 14C-Inulin and 125I-albumin into the earliest identifiable
proximal loops. There were no differences in FRAlb among the three
groups. In Protocol 2, timed-quantitative collections of tubular
fluid were obtained from proximal tubular loops. The rate of albumin
delivery to the earliest accessible loops of the proximal tubule was
significantly lower for the LP and HPE groups compared with the HP
group. For each group, albumin concentration corrected for water
absorption was not altered along the proximal tubule. The data
indicate that alterations of dietary protein intake or CEI treatment
result in large changes in the delivery of albumin at the proximal
tubule which could singularly account for the changes in urinary
albumin excretion.
Received 11 July 1995; accepted in final form 5 December 1995.
APS Manuscript Number F223-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 14 February 96