SHORT-TERM RESPONSE OF NONUREA ORGANIC OSMOLYTES IN HUMAN KIDNEY TO AWATER LOAD AND WATER-DEPRIVATION

The cells of the inner medulla of the mammalian kidney accumulate high concentrations of nonurea organic osmolytes. The organic osmolytes fo und in the kidney include glycine betaine and sorbitol. This study was designed to measure changes in the urinary excretion of glycine betai ne and sorbitol and the plasma concentration of glycine betaine in res ponse to an acute water load (20 ml/kg) or acute water deprivation in young healthy males. In response to a water load the urinary excretion of glycine betaine and sorbitol increased parallel with or shortly af ter urinary urea excretion. The increase in urinary urea and sorbitol excretions preceded maximum minute volume, whereas peak glycine betain e excretion was closely related to maximum urine minute volume. Subseq uently, urea, sorbitol, and glycine betaine excretion rates returned t o baseline. In contrast, during water deprivation no change in glycine betaine, sorbitol, and urea urinary excretions occurred during the st udy period. Plasma glycine betaine concentration was stable during bot h diuresis and antidiuresis. We conclude that the organic osmolytes gl ycine betaine and sorbitol are components of a physiological and dynam ic system in response to an acute water diuresis.