Effect of reoxygenation on PAI-1 expression and secretion. PAI-1 concentrations in cell lysates (A and B) and cell culture supernatants (C and D) of BHY and FaDu cells were determined by ELISA. Two parallel dishes were exposed to hypoxic conditions (■) and two to normoxic (□) conditions for 24 h. Subsequently, cell lysates and supernatants from one hypoxic (= 24hH) and one normoxic (= 24hN) dish were prepared or isolated, respectively. In the remaining two dishes, the medium was changed (/indicates medium change) and cells were further kept for 24 h under normoxic conditions (= 24hH/24hN and 24hN/24hN, respectively). Mean values ± S.E.M. of at least four independent experiments, each analyzed in duplicate, are shown relative to the mean normoxic value at the time of medium change (24hN). Associated significance of each sample vs. the normoxic standard (24hN) is indicated (*p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001). Additionally, the significance of the reoxygenated sample (24hH/24hN) vs. the hypoxic sample (24hH) is indicated in D.