BACKGROUND - The fibrinolytic system plays an important role in degrading fibrin-rich thrombi and in vascular and tissue remodeling. Elevated levels of plasminogen activator inhibitor-1 (PAI-1) can reduce the efficiency of the endogenous fibrinolytic system. Angiotensin (Ang) has been shown to regulate PAI-1 expression via the Ang type 1 (AT1) receptor in some tissues and via the AT4 receptor in cultured endothelium. The purpose of this study was to examine the tissue-specific pattern of PAI-1 expression in response to infusion of Ang II in vivo.
METHODS - Adult male Sprague-Dawley rats (N = 5 in each group) were treated with four hours of intravenous infusions of Ang II or vehicle control while mean arterial pressure (MAP) was monitored: group 1, 600 ng/kg/min Ang II; group 2, Ang II + 10 mg/kg of the AT1 receptor antagonist (AT1RA) L158-809 q2 hour; group 3, Ang II + 0.01 to 0.1 mg/kg hydralazine as required to maintain normal blood pressure; and group 4, saline-infused controls. After infusion, tissue was harvested for Northern blotting, immunohistochemical analysis, and in situ hybridization.
RESULTS - In group 1, Ang II infusion increased MAP from 105 +/- 8 to 160 +/- 9 mm Hg (mean +/- SE, P < 0. 01). Ang II induced increased expression of PAI-1 mRNA in all tissues examined from 5.1-fold in the heart, 9.7-fold in the kidney, 10.0-fold in the aorta, and up to 30.0-fold in the liver (all P < 0. 01 vs. control). While both AT1RA (group 3) and hydralazine (group 4) prevented Ang II-induced elevation in blood pressure, the Ang II-dependent expression of PAI-1 mRNA was reduced by only AT1 receptor blockade.
CONCLUSIONS - We conclude that in the rat, PAI-1 is induced in a variety of tissues by Ang II directly through the AT1 receptor, independent of its effects on blood pressure.