Year: 1981
Type: conference-paper
Abstract: Cultured bovine aortic endothelial cells (ECs) were employed to determine whether agents associated with the forming thrombus alter the fibrinolytic activity of the endothelium. The addition of thrombin to the cultures caused a rapid decrease in intracellular plasminogen activator activity (PAi) as measured by the plasminogen-dependent hydrolysis of radiolabeled fibrin. The cells were extremely sensitive to thrombin with as little as 3 ng/ml causing a 50% decrease in PAi within 30 min. This decrease 1) occurred in cells pretreated with actinomycin D, cycloheximide or colchicine, 2) was relatively specific since no decrease was initiated with trypsin, pronase, collagenase, or chymotrypsin, and 3) did not appear to result either from secretion or by direct inactivation of PA by thrombin. Thrombin inactivated with diisopropylfluorophosphate did not elicit the response. PAi returned to control levels within 6 hr after the addition of the thrombin inhibitor, hirudin. This reversal by hirudin was blocked by cycloheximide but not by actinomycin D. The decrease in PAi correlated with the disappearance of a form of PA of Mr 48,000. Other forms produced by the cells (i.e., 100,000, 74,000 and 53,000) were unaffected as revealed by polyacrylamide gel electrophoresis in the presence of SDS. We have begun to characterize the effect of thrombin on other metabolic activities of ECs. It was not mitogenic for growing or confluent cultures, did not alter the rate of RNA or protein synthesis, did not effect the release of 51 chromium from the cells, and apparently did not alter the spectrum of proteins synthesized by the cells. These results indicate that suppression of PAi activity by thrombin is dramatic, rapid, reversible and highly specific, and may be effected at the level of the actual synthesis of the molecule. The generation of thrombin at sites of vascular injury may thus protect the growing thrombus against premature, EC-mediated dissolution.
Source: Thrombosis and Haemostasis
Author: D J Loskutoff
Institution: Scripps Clinic
Language: English
Subfield: Hematology
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W2883135472