Clearance from the vascular compartment of endogenously labelled plasma fibronectin.

Plasma fibronectin is a large molecular weight glycoprotein which may have both opsonic and structural adhesive roles. Fibronectin deficiency has been documented in patients especially early after trauma or burn as well as during sepsis following injury. In this study, the disappearance of fibronectin from the blood was studied in rats utilizing plasma fibronectin metabolically labelled with 75Se-selenomethionine. After injection of 75Se-selenomethionine, the maximum specific activity of endogenously labelled plasma fibronectin, the observed at 4 hours. Thereafter, it declined in a non-monoexponential fashion in association with depletion of the precursor. Labelled 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 unlabelled plasma fibronectin. Following intravenous injection of 75Se plasma fibronectin, its disappearance from plasma manifested two phases. The first was an initial fast disappearance of a small amount of fibronectin, reflecting distribution between plasma and interstitial compartments. The second was a slower disappearance phase with a half-time (T 1/2) of at least 15 hours. Infusion of gelatin-coated particles, which are rapidly cleared by RE cells in the liver and spleen, enhanced the disappearance of 75Se fibronectin from the plasma. These data suggest that the normal rate of fibronectin disappearance from the vascular space is quite fast. Utilization of this experimental approach may provide valuable data on fibronectin kinetics as influenced by trauma and burn.