Elevated intraluminal pressure inhibits vascular tissue plasminogen activator secretion and downregulates its gene expression

We recently discovered that patients with essential hypertension have a mar kedly impaired capacity for stimulated release of tissue plasminogen activa tor (tPA) from vascular endothelium. This defect may reduce the chance of t imely spontaneous thrombolysis in case of an atherothrombotic event. We now investigated whether increased intraluminal pressure as such may depress v ascular tPA release or downregulate its gene expression. Segments of human umbilical veins were studied in a new computerized vascular perfusion model under steady laminar flow conditions for 3 or 6 hours. Paired segments wer e perfused at high or physiological intraluminal pressure (40 versus 20 mm Hg) under identical shear stress (10 dyne/cm(2)). Quantitative immunohistoc hemical evaluation of cellular tPA immunoreactivity was performed on paraff in-embedded 5-mu m vascular sections. tPA mRNA in endothelial cells was qua ntified with reverse transcription real-time TaqMan polymerase chain reacti on with GAPDH as endogenous control. Secretion of tPA into perfusion medium was evaluated with SDS-PAGE and Western blotting, followed by densitometri c quantification. High-pressure perfusion downregulated tPA gene expression with a 38% decrease in tPA mRNA levels (P=0.01) compared with vessels perf used under normal intraluminal pressure. tPA release into the perfusion med ium was markedly suppressed by high pressure (P<0.01 ANOVA). The intracellu lar storage pool of tPA was reduced after 6 but not 3 hours. Thus, elevated intraluminal pressure downregulates tPA gene and protein expression and in hibits its release from the endothelium independently of shear stress. The defective capacity for stimulated tPA release that we demonstrated in patie nts with essential hypertension might thus be an effect of the elevated int raluminal pressure per se.