Diffusion of tritiated water into collecting duct urine in the dog

¹ Department of Physiology, Washington University School of Medicine, Saint Louis, Missouri

When tritiated water is infused during stopped flow in the dog the renal papilla is 8.7% as well labeled as is the cortex, when no urine is permitted to escape. With urine escape, the first urine from the collecting ducts is only 4.5% as well labeled as is the cortex, and the last urine (cumulative volume up to 4.5 ml) is considerably less labeled than are the papillae from which it has just emerged. We thus find that in our present series (kidneys frozen before sectioning), as well as in our earlier series with nonfrozen kidneys, diffusion equilibration of tritiated water between papilla tissue water and collecting duct urine is incomplete in the dog.

Key Words: collecting duct permeability • permeability to water • water equilibration in collecting ducts

Submitted on April 11, 1963