The magnitude of the lowering of P if varies with the inflammatory response. Several growth factors and cytokines, including the platelet-derived growth factor BB, are able to reverse a lowering of P if and restore the normal compaction of the ECM. The molecular mechanisms involved in the lowering of P if include the release of cellular tension exerted on the collagen and microfibril networks in the connective tissue via the collagen-binding ОІ 1-integrins, thereby allowing the glycosaminoglycan ground substance, which is normally underhydrated, to expand and take up fluid. Contrary to this commonly accepted view, P if can become an active force and create a fluid flux across the capillaries in several inflammatory reactions and trauma situations rather than limit the changes occurring. The fluid volume in the interstitial space is normally regulated within narrow limits by automatic re-adjustment of the interstitial hydrostatic and colloid osmotic pressures in response to perturbations in capillary filtration and by the lymphatics.

This review will summarize current knowledge on the role of the extracellular matrix (ECM) in general and on the interstitial fluid pressure ( P if) in particular with regard to their importance in transcapillary exchange.

Interstital fluid image