Effect of aprotinin on hormone-modulated tube formation. hMVEC were cultured on three-dimensional fibrin matrices in incubation medium containing 20 ng/mL bFGF and 20 ng/mL TNF-α, and the appropriate hormone (1 μmol/L 9-cis RA or 1 μmol/L dexamethasone) or vehicle (con). For comparison, cells incubated in the absence of bFGF and TNF-α (−BT) were included. An inhibitor of plasmin activity, aprotinin (100 KIU/mL), was added at the start of the experiment. Total tube-length/cm² ± standard error of mean (SEM) was determined of triplicate wells as described in Materials and Methods.