Enhancement of renal concentrating ability in the dog by urea and related compounds

¹ Department of Physiology, University of California Medical Center, San Francisco, California

Experiments were performed on vasopressin-infused dogs to test the effect on renal concentrating ability of acute administration of urea and seven other organic nonelectrolytes. In each experiment a control assessment of concentrating ability was obtained during administration of mannitol. This was followed by administration of a test compound in an amount designed to maintain the previous rate of solute excretion. When compared to control values, urine osmolality was significantly higher during administration of urea, methylurea, acetamide, 1,2-propanediol and 1,3-dimethylurea, but not during administration of thiourea, glycerol, or hexamethylenetetramine. Others have suggested that the enhancement of concentrating ability by urea is related to the unique ability of urea to diffuse through the collecting-duct membranes. In the present study, there appeared to be no simple correspondence between the degree to which urine osmolality increased and the physical properties generally recognized to affect membrane permeation: oil:water partition coefficient, molecular size, or specific chemical groups.

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