Renal sorbitol, myo-inositol and glycerophosphorylcholine in streptozotocin-diabetic rats.

The polyols, sorbitol and myo-inositol, seem to be involved in the development of diabetic complications of different organs. High concentrations of both polyols were found in kidney medulla in addition to trimethylamines. To investigate the influence of diabetes mellitus on the regulation of both polyols and glycerophosphorylcholine in kidney, these osmolytes were quantitated enzymatically along the corticopapillary axis in untreated, streptozotocin-diabetic and insulin-treated streptozotocin-diabetic rats. In control animals three individual osmolyte patterns were found: a steep gradient of sorbitol in the papilla, increasing amounts of glycerophosphorylcholine from the outer medulla to the papilla, and nearly equal amounts of myo-inositol in the renal medulla, decreasing towards the cortex. Diabetic rats exhibit an up to fourfold increase of inner medullary sorbitol, whereas myo-inositol was only elevated in the outer medulla. Glycerophosphorylcholine was lowered in the papillary tip and elevated in the outer medulla and cortex. Insulin treatment reduced sorbitol to a concentration between those of diabetic and control rats, caused a restoration of glycerophosphorylcholine in the papillary tip and outer medulla to control values, and increased cortical myo-inositol. These data confirm previous in vitro data, which show that papillary sorbitol specifically increases in hyperglycaemic states, thereby counteracting the increased extracellular tonicity due to elevated tissue glucose concentrations. Imbalance of extra- vs intracellular osmolality during insulin treatment may be involved in the pathomechanism of renal papillary necrosis.