To identify events and mechanisms that might contribute to the poor reversibility of diabetic complications, we examined whether diabetes or high glucose induces changes in gene expression and whether such changes outlast the presence of the metabolic abnormalities. The study focused on fibronectin because the increased amounts of this glycoprotein found in diabetic tissues and thickened basement membranes are as yet unexplained. In streptozotocin-induced diabetic rats, fibronectin mRNA levels were increased to 304 +/- 295% of control (mean +/- SD) in the kidney cortex (P less than 0.02), and to 271 +/- 273% of control in the heart (P less than 0.02), while actin mRNA levels remained unchanged. Elevation of fibronectin mRNA persisted for weeks after restoration of near-normoglycemia. In cultured human endothelial cells, high glucose-induced overexpression of fibronectin and collagen IV remained detectable after replating and multiple cell divisions in the absence of high glucose. Cells shifted to normal-glucose medium after prolonged exposure to high glucose also exhibited a proliferative advantage over cells chronically maintained in normal glucose. Thus, diabetes increases fibronectin expression in tissues that are known targets of the complications, and the effect is not readily reversible. The in vitro studies suggest that hyperglycemia may be responsible for these events through induction of self-perpetuating changes in gene expression.