Osmolar Renal Concentrating Ability in Healthy Young Men and Hospitalized Patients without Renal Disease

RENAL concentrating ability in response to an antidiuretic stimulus presumably is limited by a maximum urine osmotic pressure or osmotic urine-plasma gradient or ratio. Hence, the determination of urine and plasma osmolality by freezing-point depression in the hydropenic state or after vasopressin administration should make possible the precise measurement of the concentrating function. Nevertheless, reported "normal" values for maximal osmolar concentrating ability have varied over a wide range.^{1 2 3 4} Possible causes for this variation include the effect of dietary protein,⁵ previous state of hydration,^{2 , 6} small changes in solute excretion⁷ and changes in renal blood flow or filtration rate.^{8 9 10} In the present . . .