Relative Rates of Passage of H¹H³O¹⁶ and of H¹₂O¹⁸ Across Pulmonary Capillary Vessels in the Dog

¹ From the Departments of Medicine and Physiological Chemistry, Johns Hopkins School of Medicine, and the Medical Division, Baltimore City Hospitals, Baltimore, Maryland

Relative rates of passage of H¹H³O¹⁶ and H¹₂O¹⁸ across the pulmonary capillaries of the dog have been examined. No significant difference has been found. In previous studies (Am. J. Physiol. 178: 203, 1954), no significant difference was found in the relative rates of passage of H¹H²O¹⁶ and H¹H³O¹⁶. It is concluded that H¹₂O¹⁸, H¹H²O¹⁶ and H¹H³O¹⁶ may be used interchangeably as tracers for each other and as tracers for ordinary water, H¹₂O¹⁶, in biological systems in which physico-chemical processes such as diffusion are involved.