Service of urea in renal water conservation

Abstract

Rats allowed water ad libitum were injected with vasopressin tannate in oil to insure formation of maximally concentrated urine. Low protein diet was fed to which were added varying amounts of sodium chloride with or without urea. Through a wide range of urinary excretion rates of nonurea solute the feeding of urea resulted in formation of lesser volumes of more highly concentrated urine. This reduction of the renal water requirement in the urea-fed rats was most marked when the ratio in urine between urea and nonurea solutes had a value of 0.3–0.5. When present in urine in amounts equal to or greater than osmoles of nonurea solute, urea increased the renal water requirement.