Differential Roles of AT1and AT2Receptor Subtypes in Vascular Trophic and Phenotypic Changes in Response to Stimulation With Angiotensin II

Abstract

The aim of this study was to investigate the roles of angiotensin II (Ang II) receptor subtypes 1 (AT1) and 2 (AT2) in producing vascular wall hypertrophy and qualitative changes in smooth muscle cell gene expression. Wistar rats were treated for 23 days with osmotic minipumps containing solvent and either Ang II (120 ng·kg−1·min−1) orPD123319(30 mg·kg−1·d−1), an AT2receptor antagonist. In addition, rats receiving solvent and either Ang II orPD123319were given losartan, an AT1receptor antagonist, in the drinking water (10 mg·kg−1·d−1). Vascular wall hypertrophy and smooth muscle phenotype were characterized by morphometric analysis combined with immunohistochemistry. Ang II–induced hypertension was associated with the development of medial hypertrophy of the aorta and coronary arteries accompanied by reversion of vascular smooth muscle cells (VSMCs) toward an immature phenotype, as shown by the expression of cellular fibronectin and nonmuscle myosin. Losartan treatment, which restored normal arterial pressure, prevented all these changes.PD123319treatment, which had no effect on blood pressure, prevented only vascular hypertrophy, with no effect on VSMC phenotype. Administration of only losartan to normal rats reproduced the Ang II–induced vascular hypertrophy, with no effect on VSMC phenotype. Taken together, these results suggest that (1) the trophic effect of Ang II on VSMCs is mediated via AT2receptor subtypes and (2) changes in VSMC phenotypes are triggered mainly through AT1receptor subtypes.