Secretion of tissue-type plasminogen activator and plasminogen activator inhibitor by cultured human endothelial cells: modulation by thrombin, endotoxin, and histamine.

Primary cultures of pooled endothelial cells obtained from four to six human umbilical cord veins were grown to confluency in M 199 cell culture medium containing 20% human serum. The secretion of tissue-type plasminogen activator antigen (t-PA Ag) and fast-acting plasminogen activator inhibitor activity (PA-I activity) was measured in the conditioned medium after incubation of confluent cultures with serum-free medium for 24 hours (1.5 ml/25 cm2 cell surface). The baseline production of t-PA Ag was 2.7 +/- 1.4 ng/ml (mean +/- SD) and of PA-I activity 36 +/- 18 IU/ml. Stimulation with thrombin resulted in a dose-dependent and time-dependent increase of the secretion of both components. At 1 NIH U thrombin per milliliter, a fourfold increase of t-PA Ag and a twofold increase of PA-I activity were observed. This effect was dependent on a free active site in thrombin and specific protein synthesis (inhibited by cycloheximide and dactinomycin) but unrelated to prostacyclin synthesis (no effect of aspirin or indomethacin). No free t-PA activity could be demonstrated on fibrin plates in conditioned medium from either stimulated or nonstimulated endothelial cell cultures. Endotoxin stimulation resulted in a specific secretion of PA-I activity but not of t-PA Ag, whereas histamine stimulation at concentrations of 0.1 to 1 mumol/L caused a specific secretion of t-PA Ag but not of PA-I. These findings indicate that the secretion of t-PA Ag and PA-I activity are not necessarily coupled.(ABSTRACT TRUNCATED AT 250 WORDS)