Water and solute exchanges. How far have we come in 100 years? What's next?

Two approaches have been used in descriptions of transvascular exchanges and net transfers of water and small solutes. The classical approach is based on Starling's four factors, vascular and interstitial hydrostatic and osmotic pressures, and on the concept of filtration in bulk without separation of solvent water from small solutes. In a physicochemical approach based on nonequilibrium thermodynamics and on multiple indicator-dilution experiments, diffusion is considered the dominant mechanism in transvascular exchanges of water with net transfers related primarily to the permeability and net passage of small solutes such as sodium and chloride ions (osmotic buffering).

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).

Pulmonary vascular extraction and distribution of antipyrine with alveolar flooding.

Transport characteristics of antipyrine (AP), 22Na+, and tritiated water (THO) were assessed in dog lungs by multiple indicator-dilution experiments in vivo with anesthesia and in isolated perfused preparations before and after alveolar flooding. In controls, outflow patterns of AP and THO were nearly identical. In flooding, AP and THO patterns separated.

The diffusional transport of water and small solutes in isolated endothelial cells and erythrocytes.

The diffusional permeability coefficients, PD, for tritiated water (3HHO) 14C-antipyrine (AP) and 14C-iodoantipyrine (IAP) in isolated calf pulmonary artery endothelial cells and dog erythrocytes are measured with the linear diffusion technique at 11.5, 15, 20 and 37 degrees C. The PD values for both cell populations follow the sequence 3HHO > IAP > AP at each of the temperatures.