Absorption of phenol red from the human lung

Pulmonary absorption of phenol red was studied in normal subjects. Phenol red was administered by intratracheal injection and its urinary excretion was used as an index of pulmonary absorption. Doses ranging from 3 to 30 mg were given to two subjects and urinary phenol red excretion was found to be rate limited. That this effect occurred in the lung was shown by giving the dye intravenously to one subject. A linear relationship between dose and urinary excretion was then observed. Intratracheal p-aminohippurate did not reduce pulmonary absorption of phenol red in one subject. Pulmonary absorption of phenol red dissolved in 0-9% saline and 0-18% saline was compared in nine subjects. Dye absorption was three times greater when it was given in 0-18% saline. When the saline concentration of phenol red doses was held constant there was a linear relationship between the intratracheal dose and urinary excretion in one subject. These results suggest that phenol red is absorbed from the lung by passive diffusion. They also show the importance of solvent effects when studying pulmonary absorption of a substance.