Abstract 5535: In Vivo Activation Of Myocardial At2 Receptor Expression By Endogenous No And Pentaerythritol Tetranitrate
There are many vascular signaling interactions between the vascular endothelial NO system and the renin-angiotensin-system. We hypothesized that endothelial NO might impact on the expression of angiotensin (AT) type 1 (AT1) and type 2 (AT2) receptors. We generated mice with an endothelial-specific overexpression of endothelial NO•-synthase (eNOS) using the Tie-2 promotor. Two of these lines were characterized by eNOS-Western blot analyses and blood pressure measurements in comparison to transgene negative controls. In addition, C57Bl/6 mice were fed with either 6 or 60 mg pentaerythritol tetranitrate (PETN) for 4 weeks and characterized as well. Analysis of line 1 of transgenic eNOS mice (1-eNOS) showed a 2.3±0.15 fold higher aortic expression of eNOS and a reduction of blood pressure to 109.6±2.0 mmHg (P<0.01, n=4–6). Line 2 of transgenic eNOS mice (2-eNOS) showed a 3.3±0.3 fold higher aortic expression of eNOS and a reduction of blood pressure to 105.0±3.0 mmHg (n=6, P<0.01). Treatment of 2-eNOS with the NOS-inhibitor L-nitroarginine (L-NAME) for 30 days inhibited the difference in blood pressure suggesting that this effect is due to increased bioavailability of endogenous nitric oxide (NO). In lungs and left ventricular myocardium of 2-eNOS the expression of AT1 receptors was similar to the controls (121.6±14.77%, and 100.1±12.43%, respectively, n=8, P>0.05). In striking contrast, the expression of AT2 receptors was increased by endothelial overexpression of eNOS in a gene-dose-dependent manner in the myocardium. In 1-eNOS the increase was 134.3±10.66% (P<0.05) and in 2-eNOS the increase was 177.7±20.93% (P<0.05). In lung tissue the increase of AT2 receptor expression in line 2 amounted to 139.3±13.73% (P<0.05) and to 131.8±.7 in line 1 of eNOS transgenic mice suggesting a vascular rather than a cardiomyocyte effect. Furthermore, preliminary experiments showed a significant increase of AT2 receptor expression in myocardial tissue of PETN-fed mice and a significant decrease in myocardial tissue of L-NAME-fed mice (respectively, n=4, P<0.05). These results show that NO can upregulate vascular AT2 receptor expression in the lung and in the myocardium in-vivo. This newly discovered regulation might contribute to vasoprotective effects of NO.