Clearance from the Vascular Compartment of Endogenously Labelled Plasma Fibronectin

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Abstract
Plasma fibronectin is a large MW glycoprotein which may have both opsonic and structural adhesive roles. Fibronectin deficiency was documented in patients especially early after trauma or burn as well as during sepsis following injury. The disappearance of fibronectin from the blood was studied in rats utilizing plasma fibronectin metabolically labeled with 75Se-selenomethionine. After injection of 75Se-selenomethionine, the maximum specific activity of endogenously labeled plasma fibronectin was observed at 4 h. Thereafter, it declined in a non-monoexponential fashion in association with depletion of the precursor. Labeled 75Se fibronectin was purified from donor rat plasma by gelatin-sepharose affinity chromatography. It retained its electrophoretic mobility, gelatin adherence and opsonic activity similar to that of unlabeled plasma fibronectin. Following i.v. injection of 75Se plasma fibronectin, its disappearance from plasma manifested 2 pahses. The 1st was an initial fast disappearance of a small amount of fibronectin, reflecting distribution between plasma and interstitial compartments. The 2nd was a slower disappearance phase with a half-time (T1/2) of at least 15 h. Infusion of gelatin-coated particles, which are rapidly cleared by RES cells in the liver and spleen, enhanced the disappearance of 75Se fibronectin from the plasma. The normal rate of fibronectin disappearance from the vascular space is quite fast. Utilization of ths experimental approach may provide valuable data on fibronectin kinetics as influenced by trauma and burn.