AJP - Renal Physiology, Vol 248, Issue 1 31-F42, Copyright © 1985 by American Physiological Society
Physiological and morphological responses of the rat kidney to reduced dietary protein
B. Schmidt-Nielsen, J. M. Barrett, B. Graves and B. Crossley
Renal physiological and morphological adjustments to a reduced protein diet
were studied in young Munich-Wistar rats. Two groups of animals were used
for the correlative physiological-morphological studies: normal protein
(NP, 24% dietary protein) rats and reduced protein (LP, 8% dietary protein)
rats. Both groups were fed their respective diets for 4-5 wk and had free
access to drinking water. Physiological measurements of GFR and urea
clearance were made on five animals from each group. These data showed that
the changes in renal function specifically and almost exclusively affected
the handling of urea. There was no difference in GFR between the NP and LP
rats. Urea clearance was substantially reduced in LP rats. Morphological
analyses were made on perfusion-fixed kidneys of five animals from each
group. Selected slices were examined and photographed by light and electron
microscopy. These data showed no difference in size and number of elements
within the vascular bundles but showed significantly smaller lumina of the
thin limbs of the short-looped nephrons and a significant thinning of the
wall of the thin descending limbs of the long-looped nephrons. These
morphological changes may in part be responsible for the observed
physiological adjustments to a reduced protein diet. An additional group of
rats (6 NP and 5 LP, all dehydrated) were analyzed for distribution of
solutes within the inner medulla. The data showed that the concentration of
urea, but not that of Na+, was reduced at the papillary tip in LP rats.
