Role and regulation of glycerophosphorylcholine in rat renal papilla.

Glycerophosphorylcholine (GPC)--an organic solute which is considered to be involved in cellular osmoregulation in the renal medulla--was determined by means of an enzymatic assay in various zones of the rat kidney and in papillary tubule suspensions. In antidiuresis, GPC content in cortex, outer medulla and papillary tip was 0.64, 14.6, and 108.9 mmol/kg fresh weight, respectively. Significant concentrations of GPC could not be detected in the urine or in the peripheral plasma. The sharp increase in GPC concentration from cortex to papillary tip was partially abolished by the induction of diuresis by either waterloading or furosemide. These manoeuvres, however, did not change cortical GPC content. Papillary tubule suspensions prepared from hydropenic rats contained only slightly less GPC per g protein than whole papillae from antidiuretic animals. Incubation of tubules over 120 min did not lead to a significant loss of GPC which is in accordance with the low activity of GPC degrading enzymes in papillary tissue. The results confirm the intracellular localization of GPC and provide further evidence that this substance plays a substantial role in the osmoregulation of renal papillary cells.