In vivo study of AT1 and AT2 angiotensin receptors in apoptosis in rat blood vessels

In vitro experiments suggest that angiotensin II (Ang II) may cause growth via angiotensin type I (AT(1)) receptors and apoptosis via angiotensin type 2 (AT(2)) receptors To answer the question of whether AT(1) or AT(2) receptor activation could induce apoptosis in the vasculature in vivo, Wistar rats were infused for 7 days with Ang II (120 ng . kg(-1) . min(-1) subcutaneously) and treated with the AT(2) receptor antagonist PD 123319 (30 mg . kg(-1) . d(-1) subcutaneously) or the AT(1) receptor antagonist losartan (10 mg . kg(-1) . d(-1) orally). Apoptosis in thoracic aorta was quantified by radiolabeled DNA laddering and by terminal deoxynucleotide transferase-mediated dUTP nick end-labeling. The expression of p53, bar, bcl-2, and caspase-3, which play critical roles in apoptotic signaling, was examined by Western blot analysis. The mRNA expression of AT(1) and AT(2) receptors was determined by reverse transcription-polymerase chain reaction. The increase in systolic: blood pressure and aortic growth induced by Ang II infusion was completely prevented by losartan alone or losartan given with PD 123319, whereas PD 123319 resulted in-a greater increase in systolic blood pressure and aortic growth;than Ang II alone. Radiolabeled DNA laddering showed that Ang II infusion+/-losartan or PD 123319 significantly increased apoptosis (147+/-8% 178+/-20%, and 238+/-41%, respectively, P<0.05 compared with control). Expression: of bar and active forms of caspase-3 was increased in the Ang II+PD 123319 group, whereas the expression of p53 and bcl-2 was not significantly different in all groups. The expression of AT(1) and AT(2) receptor mRNA was downregulated by losartan and PD 123319, respectively. Thus, when AT(1) or AT(2) receptors are stimulated in vivo, apoptosis is enhanced in the media of blood vessels. In the case of AT(1) receptor stimulation, this may occur secondary to vascular growth and modulate the latter. Both bar and caspase-3 participate in the pathways of apoptosis triggered by in vivo AT(1) receptor stimulation.