Production of Hypertonic Urine in the Absence of Pituitary Antidiuretic Hormone1

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Abstract
In water-loaded dogs compression of one renal artery leads to a rise in the concentration of the urine produced by the affected kidney. It is thus possible for one kidney to produce urine hypertonic to plasma while the other kidney excretes water at a maximal rate. The changes were shown not to be due to sensitization of the experimental kidney to the action of minimal amounts of ADH. The important factor is believed to be the reduction of the rate of glomerular filtration and thus the filtered load of Na and chloride in each nephron. Since reduced amounts of Na and chloride reach the segment responsible for dilution of the urine, the extent to which the urine can be diluted by abstraction of these ions is limited. Diffusion of water from the diluted urine through the relatively impermeable tubule results in delivery of a small volume of only slightly diluted urine to the concentrating segment. The concentrating mechanism, operating essentially without dependence on ADH, is able to remove enough water to render the urine hypertonic to plasma. The role of ADH is interpreted as that of increasing the permeability of the diluting and possibly the concentrating segments to the movement of water along osmotic gradients. Factors having to do with the load and disposition of Na as well as ADH must be considered in the interpretation of changes in urine concentration.