Pulmonary distribution of iodoantipyrine: temperature and lipid solubility effects

In multiple indicator-dilution studies in rat and dog lungs, we have found that the distribution of iodoantipyrine (IAP) is not limited by the endothelium at a temperature > 7 degrees C but is barrier limited at the epithelium at a temperature < 15 degrees C (permeability coefficient of 6.3 x 10(-5) cm/s at 8 degrees C). IAP extraction from the vascular surface to the tissues is greater than those of antipyrine (AP) and tritiated water (THO). IAP transmittance from the alveolar surface to the vascular compartment is smaller than those of AP and THO: a lung lipid compartment, probably in the lamellar bodies of the type II cells, is more accessible to IAP than to AP or THO because IAP has a higher oil-to-water distribution coefficient. Our mathematical model takes into account these matters and also the low surface density of the type II cells: some of the IAP may bypass the lipid compartment. Lipid may affect the transit of solutes with high oil-to-water distribution coefficients in the lungs and across the alveolar-capillary barrier.