Vascular hypertrophy and increased P70S6 kinase in mice lacking the angiotensin II AT(2) receptor

Angiotensin II activates 2 distinct G protein-coupled receptors, the AT(1) and AT(2) receptors. Most of the known cardiovascular effects of angiotensin II are mediated by the AT(1) receptor subtype. The aim of the present study was to test whether deletion of the AT(2) receptor gene in mice (AT(2)-KO mice) leads to long-term functional or structural alterations in the cardiovascular system.

In vivo pressure responses to angiotensin II or the alpha(1)-adrenergic receptor agonist phenylephrine were greatly enhanced in AT(2)-KO mice. Deletion of the angiotensin AT(2) receptor did not lead to a compensatory increase of the activity of the circulating renin-angiotensin system, and arterial blood pressure was identical in wild-type control mice (WT) and AT(2)-KO mice. Cardiac contractility as assessed by LV catheterization and by rapid MRI also did not differ between AT(2)-KO and WT mice. Isolated femoral arteries from AT(2)-KO mice, however, showed enhanced vasoconstriction to angiotensin II, norepinephrine, and K(+) depolarization compared with WT. Morphometric analysis of large and small femoral arteries revealed a significant hypertrophy of media smooth muscle cells. Phospho-P70S6 kinase levels were significantly increased in aortas from AT(2)-KO mice compared with WT mice. Treatment of mice with an ACE inhibitor for 8 weeks abolished the increased pressure responsiveness, vascular hypertrophy, and enhanced P70S6 kinase phosphorylation in AT(2)-KO mice.

These results indicate that vascular AT(2) receptors inhibit the activity and, hence, hypertrophic signaling by the P70S6 kinase in vivo and thus are important regulators of vascular structure and function.