This was shown by Michel and Phillips in 1987 using the Landis isolated perfused capillary preparation. Plot the pressure filtration rate curve you would expect from a single capillary perfusion experiment where the extravascular oncotic pressure is set at 25mmHg. Important references are in italics. Michel and Curry's Physiological Review paper has an excellent description of endothelial cell behaviour during inflammation. Copies of the Neal, MacDonald, Feng and Bates Microcirc reviews are in my office.
Endothelial cells line the vessel wall and form a tight overlapping barrier to macromolecules.
The endothelial junctions are the primary route for hydrophilic solutes to move across the endothelial barrier. The tight junctions are discontinuous and solutes may pass around the discontinuities. If capillary pressure falls, then the filtration rate falls, until the rate of diffusion from both the plasma protein through the cleft and the interstitial protein back into the cleft, restores the oncotic pressure difference, and filtration is restored. Solute permeability is defined by Fick's law, and is controlled by the restricted diffusion coefficient of the solute, the area of the pores relative to the area of the vessel, the number of pores and their length, and the solute size. The reflection coefficient depends on the pore size and the solute size, and increases with increasing pore size.