The permeability of fibrin network developed in human plasma.

Fibrin network permeability has an important role in thrombosis and inflammation since it influences the rate of transport of macromolecules through the network by convection. The conditions of polymerization of fibrin determine the network permeability and this has been attributed to variability in fibrin fibre thickness. Inconsistencies between values for fibrin fibre thickness derived from turbidity and permeability were examined. Networks were developed from human plasma by the addition of thrombin and network polymerization was modified pharmacologically. Dextran (MW 70,000) and poloxamer 188 both increased, and lauryl sulphate decreased, network permeability and network turbidity. Network fibre thickness was consistently higher when derived from permeability than from turbidity. Network permeability was significantly more susceptible to pharmacological manipulation by these agents than network turbidity. These inconsistencies were attributed to variation in the arrangement of the network fibres such as inhomogeneity of network fibre distribution and to fibre aggregation or alignment. Collectively these factors prohibit the derivation of fibrin fibre thickness from permeability. The dimensionless permeability (network permeability/(fibre radius)2) was used as an index of network fibre arrangement and found to be readily modified pharmacologically. Physiological and pharmacological regulation of fibrin network permeability may be predominantly mediated through modification of fibre arrangement and not through fibre thickness.