Elevated blood pressure in normotensive rats produced by 'knockdown' of the angiotensin type 2 receptor

Most of our knowledge of the function of the angiotensin type 2 receptor (AT(2)R) has been obtained from transgenic mouse models. The aim of the present study was to investigate the role of the AT(2)R in normotensive Sprague-Dawley (SD) rats by using antisense gene transfer technology to 'knockdown' this specific receptor subtype. A retroviral vector containing full-length AT(2)R antisense cDNA (AT(2)R-AS) was constructed and the effectiveness of the transduction of AT(2)R-AS was studied in vitro. In subsequent in vivo studies, 5-day-old normotensive SD rats received a single intracardiac bolus (25 microl) of AT(2)R-AS viral particles. When animals reached adulthood, direct blood pressure (BP), and both pressor and dipsogenic responses to angiotensin II were investigated. Long-lasting expression of the AT(2)R-AS transcript and a reduction in mRNA and binding of the AT(2)R was observed in vitro. Expression of AT(2)R-AS transcript was maintained for 90 days in heart, kidney, lung and brain, indicating a high degree of transgene transduction in vivo. As adults, systolic BP and the pressor responses to angiotensin were significantly elevated in AT(2)R-AS-treated rats. However, AT(2)R-AS-treated rats displayed significantly reduced dipsogenic responses to both angiotensin and water deprivation. Collectively, these data demonstrate that a single neonatal injection of the retroviral vector containing antisense to the AT(2) receptors in rats results in similar cardiovascular and dipsogenic responses as reported in AT(2)R knockout mice. The actions of the AT(2) receptors appear to be antagonistic to the cardiovascular actions of the AT(1) receptors, whereas AT(1) and AT(2) receptors appear to act synergistically in the regulation of water intake.