Albumin modulation of capillary permeability: test of an adsorption mechanism.

We investigated further the mechanism whereby albumin interacts with the walls of capillary blood vessels to maintain normal permeability properties. In individually perfused capillaries of frog mesentery, hydraulic conductivity was measured as the albumin perfusate concentration was first reduced in three steps from 0.1 to 0 g/dl (intermediate concns 0.01 and 0.001 g/dl), then increased in up to four steps to 1 g/dl (intermediate concns 0.001, 0.01, and 0.1 g/dl). The albumin concentration required to return hydraulic conductivity toward control values, following Ringer perfusion, was at least an order of magnitude larger than that required to maintain permeability close to control values prior to Ringer perfusion. The experiments indicate that the affinity of albumin for binding sites on the capillary wall following Ringer perfusion is less than the albumin affinity for binding sites after the capillary has been perfused with solutions containing 0.1 g/dl albumin. Before the hysteresis of hydraulic conductivity on albumin concentration can be understood, the factors determining the transport of albumin into the membrane must be investigated further.