Intrarenal Distribution Of Urea + Related Compounds - Effects Of Nitrogen Intake

concentrations in the inner medulla are higher than in the urine, whereas in rats on high-protein diet the urea concentra- tion in the inner medulla is lower than in the urine. The specific activity of urea-Cl4 I hr after subcutaneous injection is ap- proximately the same in plasma, renal cortex, and outer and inner medulla. The intrarenal distributions of acetamide and methylurea show the same pattern and are influenced by nitrogen intake in the same way as urea, whereas thiourea concentrations in urine are always higher than in the papilla. It is concluded a) that urea formation cannot account for papilla urea concentrations higher than urine concentrations; b) that the handling of urea and related compounds in the collecting duct changes in a similar way with changes in the nitrogen and salt intake; and c) that in the rat urea, methylurea, and acet- amide are either reabsorbed in the collecting duct against their concentration gradients or bound by the papilla tissue.