Diffusion of labeled water and lipophilic solutes in the lung

A perfused, in situ rabbit lung preparation was used to study the diffusion of tritiated water and labeled lipophilic solutes from the airways into the pulmonary vasculature. Following instillation into the airways, initial concentrations of labeled ethanol and butanol in the left atrial outflow usually exceeded those of 3H2O when the lungs were perfused at 37 degrees. In contrast, initial concentrations of [14C]acetone equaled 3H2O concentrations, and those of [14C]antipyrine were below 3H2O concentrations. Increasing the rate of perfusion increased concentrations of the labeled butanol and acetone but decreased that of antipyrine relative to 3H2O. This suggests that the tissues separating the gaseous and vascular compartments of the lung are more permeable to 3H2O than to antipyrine but less permeable to 3H2O than to the alcohols and acetone. Cooling slowed permeation of ethanol and antipyrine relative to 3H2O but seemed to slow diffusion of butanol less than that of 3H2O. These differences cannot be related to movement in the aqueous phase and suggest that cooling slows solute diffusion through lipid membranes. This phenomenon appears to be related to the activation energy of each molecule between the aqueous and lipid phases rather than a phase change in the membrane. 3H2O seems to diffuse through aqueous regions of the air-perfusate barrier.