The proposed studies will analyze the structural properties of chick hepatocyte fibronectin with a specific aim of comparing these properties with that of previously well-characterized chicken plasma and cellular fibronectins. A major objective is to determine whether or not the hepatocyte, which synthesizes the majority of plasma proteins, is also the major cellular site of plasma fibronectin synthesis. In order to establish the cellular origin(s) of plasma fibronectin, we will examine the synthesis and secretion of fibronectin by primary chick liver parenchymal cells maintained in a non-parenchymal serum-free, hormone-free and arginine-deficient medium to minimize non-parenchymal cell growth. We will purify and characterize the fibronectin secreted into the chick hepatocyte culture medium. We will also evaluate the possible effects on fibronectin synthesis by insulin, dexamethasone and thyroid hormones. Specific physiological factors, such as glucocorticoids, which play a role in responses such as the "acute phase" reaction during inflammatory states in vivo, may modulate liver fibronectin synthesis. Study of the effects of these hormones under the chemically-defined conditions established for this hepatocyte culture system will allow us to understand their role in determining the amount and rate of fibronectin synthesized.