Fibronectin is synthesized as an acute phase reactant in rat hepatocytes

Elevated concentrations of fibronectin were found in plasma of rats under different acute phase conditions. Untreated animals showed a plasma fibronectin concentration of 150 +/- 50 mg/l, which increased to 412 +/- 59 mg/l 24 h after subcutaneous injection of turpentine. The time course of the changes in plasma fibronectin concentration showed a peak at 24 h and a decline to normal concentrations 72 h after turpentine treatment. Additional stimulation by dexamethasone resulted in plasma fibronectin concentrations of 661 +/- 49 mg/l. No or only slight elevations of fibronectin concentrations were observed after treatment with adrenaline, thyroxine and triiodothyronine as compared with saline-injected animals. The common identity of plasma fibronectin in controls, turpentine and turpentine-dexamethasone-treated animals was shown by slab gel electrophoresis under nonreducing conditions, followed by western blot and immunofluorescence staining. One dimensional immunoelectrophoresis performed with polyclonal antibodies to human fibronectin cross-reacting with rat fibronectin (shown by Ouchterlony gel diffusion) revealed identical precipitation lines for the plasma of control and acute phase animals. Hepatocytes of turpentine-pretreated rats show a threefold increase of [14C]valine incorporation into total protein and a fourfold increase of immunoreactive radioactively labeled fibronectin in the culture medium, compared with control hepatocyte cultures. These results point to the role of hepatocytes in the synthesis of plasma fibronectin, which behaves in rats as an acute phase reactant.