Perinatal Delivery of Angiotensin Type 2 Receptor (AT2R) Antisense cDNA Increases Blood Pressure in Adult Normotensive Rats
Recent observations suggest that AT2R have a role in the counter-regulatory actions of angiotensin II (Ang II) in cardiovascular protection and angiogenesis. The objective of the current investigation was to provide evidence for this cardioprotective action of AT2R by utilizing antisense gene transfer technology in normotensive rats. A retroviral vector containing full length AT2 receptor antisense cDNA (LNSV-AT2R-AS) or missense (LNSV-AT2R-MS) was constructed. The LNSV-AT2R-AS viral particles were highly efficient in the transduction of AT2R-AS in vitro. The efficacy and effectiveness of this transduction was demonstrated by the long-lasting expression of AT2R-AS transcript and a decrease in AT2R binding. In vivo administration of LNSV-AT2R-AS resulted in similar findings. Five-day old normotensive Sprague Dawley rats received a single intracardiac bolus (25 μl) administration of LNSV-AT2R-AS viral particles (1x109 cfu/ml), which resulted in a robust expression of AT2R-AS transcript in tissues such as heart, kidney, adrenals and brain as early as five days post-delivery. Control rats received either LNSV alone or LNSV-AT2R-MS under identical conditions. The expression of AT2R-AS was persistent through adulthood indicating a high degree of transgene transduction in vivo. Mean blood pressure (BP) was elevated in the adult LNSV-AT2R-AS-treated rats when compared to the age-matched LNSV-AT2R-MS or control rats (123±5 mmHg vs. 100±9 mmHg). In addition, the pressor responses produced by Ang I and Ang II were enhanced in the LNSV-AT2R-AS- treated rats. For example, administration of 0.1 μg/Kg Ang I elicited a maximal increase in BP of 35±6 mmHg in the LNSV-AT2R-AS-treated rats compared to an increase of 23±6 mmHg in the LNSV-AT2R-MS. These observations demonstrate for the first time, that persistant inhibition of AT2R in normotensive rats influence cardiovascular responsiveness. Collectively, these data suggest that use of the AT1 receptor antagonist-based therapy, with the resultant increase in Ang II levels, might provide additional benefit to the hypertensive patient via increased AT2R stimulation.