AJP - Renal Physiology, Vol 269, Issue 5 696-F701, Copyright © 1995 by American Physiological Society
Renal inner medullary sorbitol metabolism
R. W. Grunewald, I. I. Weber and R. K. Kinne
Sektion Nephrologie, Univeristatsklinik Ulm, Germany.
Sorbitol participates in the osmoregulation of several renal cells and has
also been found in isolated inner medullary collecting duct (IMCD) cells in
primary culture. Therefore, osmotic regulation and distribution of sorbitol
and the key enzymes of sorbitol metabolism, aldose reductase and sorbitol
dehydrogenase in the renal inner medulla, were investigated in vivo under
various osmotic conditions (control, diuresis, antidiuresis). In
homogenates of the renal inner medulla of Wistar rats, the sorbitol content
correlated with the urine osmolarity [68 +/- 12 mumol/g protein (control),
28 +/- 9 mumol/g (diuresis), 110 +/- 15 mumol/g (antidiuresis)]. Similar
results were obtained for the activity of aldose reductase (sorbitol
synthesis) [25 +/- 4 U/g (control), 19 +/- 3 U/g (diuresis), and 48 +/- 7
U/g (antidiuresis)]. On the contrary, the activity of sorbitol
dehydrogenase (sorbitol degradation) was significantly increased to 1.26
+/- 0.42 U/g under diuretic conditions vs. control (0.84 +/- 0.14 U/g, P
< 0.05). These results demonstrate the correlation between the enzymes
of sorbitol synthesis and sorbitol degradation in the intact inner medulla
and the urine osmolarity in vivo. Whereas the aldose reductase activity was
2.3-fold enriched in IMCD cells, the specific activity of sorbitol
dehydrogenase was relatively increased in a preparation of enriched
interstitial cells. This distribution was not dependent on the various
diuretic conditions. These results indicate that enzymes of synthesis and
of degradation of sorbitol are osmotically regulated in vivo. Therefore,
the enzymatic activities of sorbitol synthesis appear to be primarily
located in epithelial cells, whereas enzymatic activities of sorbitol
degradation seem to be localized in interstitial cells of the renal inner
medulla.
