Many years ago, Gamble, McKhann, Butler and Tuthill (1) described "an economy of water in renal function referable to urea." Recently, experiments in the rat (2-4) and man (5) have confirmed their suggestion that the urine volume required to excrete a given solute load is reduced when urea is a principal urinary solute. An hypothesis assigning a unique role to urea in the urine concentrating pr...
