Organic solute profiles and transport in the rat renal medulla.

Renal inner medullary cells accumulate high concentrations of organic solutes. Sorbitol and glycerophosphorylcholine accumulation (concentration) increase progressively from the outer medulla to the papillary tip. Inositol accumulation is the reverse; its concentration decreases from the outer medulla to the papillary tip. Diabetes mellitus (1 week) increases sorbitol at all levels of the inner medulla, decreases glycerophosphorylcholine and has little effect on inositol. Thin slices of the inner medulla incubated in vitro concentrate inositol and choline from the medium. Although the inner medullary cells are permeable to sorbitol, membrane transport appears to play no role in its accumulation.