Physiological Reviews, Vol 71, 1081-1115, Copyright © 1991 by American Physiological Society
Renal medullary organic osmolytes
A. Garcia-Perez and M. B. Burg
Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, Bethesda, Maryland.
Sorbitol, inositol, GPC, and betaine are the predominant organic osmolytes
in renal medullary cells. They protect the cells from harmful effects of
the high interstitial NaCl and urea concentrations that occur normally in
the renal medulla with operation of the urinary concentrating mechanism.
Their levels correlate with extracellular NaCl concentration and, in the
case of GPC, also with urea. Sorbitol is synthesized from glucose in a
reaction catalyzed by aldose reductase. Inositol and betaine are
transported into the cell. Glycerophosphorylcholine synthesis is dependent
on choline. The transcription of aldose reductase and the transport of
betaine and inositol are regulated, dependent on the degree of
hypertonicity. Normal organic osmolyte regulation contributes to the
survival and growth of medullary cells in their hyperosmolal environment,
and defective regulation can damage them.
