Abstract 43: Non-Canonical AT1R/b-Arrestin2 Activation In Brain As A Regulator Of Fluid Homeostasis And Blood Pressure

Abstract

The brain renin angiotensin system (RAS) is known for its role in cardiovascular and metabolic regulation. Angiotensin II (Ang II) is the major active product of the RAS, exerting most of its physiological effects through the angiotensin type-1 receptor (AT 1 R). Canonical or G-protein-mediated signaling of the AT 1 R within the brain has long been known to induce a dipsogenic and pressor response upon Ang II stimulation. Non-canonical or β-Arrestin mediated signaling is thought to counterbalance the detrimental effects of canonical signaling. However, the non-canonical AT 1 R/β-Arrestin pathway within the brain is understudied. Therefore, it is hypothesized that β-Arrestin activation contributes to fluid homeostasis and blood pressure (BP) regulation. Global β-Arrestin1 ( Arrb 1) and β-Arrestin2 ( Arrb 2) knockout (KO) mice were employed to evaluate drinking behavior and BP with and without deoxycorticosterone acetate (DOCA). Age- and sex-matched C57BL/6J mice served as controls. Mice were subjected to the two-bottle choice paradigm, in which the animals were presented with two bottles, one containing water and one containing 0.15M saline. In the absence of DOCA, mice lacking β-Arrestin2 had increased saline intake when compared to β-Arrestin1-KO and wildtype (WT=2.2±0.2 and Arrb 1-KO=2±0.4 vs Arrb 2-KO=5±0.7 mL/day; p<0.001; n=13, 11 and 9, respectively). This resulted in a saline preference, which means mice preferred saline over water by more than 50% by volume. In the presence of DOCA, mice lacking β-Arrestin2 had increased saline intake when compared to β-Arrestin1-KO and wildtype (WT=10.6±1.2 and Arrb 1-KO=6.5±0.8 vs Arrb 2-KO=16.6±2 mL/day; p<0.001; n=13, 11 and 9, respectively). However, these mice did not develop a saline preference. Preliminarily, β-Arrestin2-KO mice exhibited higher BP when compared to WT at baseline (WT=108±5 vs Arrb 2-KO=124±6 mmHg; n=2), which was exacerbated in response to DOCA (WT=122±6 vs Arrb 2-KO=140±5 mmHg; n=2). These findings suggest that β-Arrestin2 might counterbalance effects of canonical activation of the AT 1 R through G proteins. Overall, β-Arrestin2 appears to protect against cardiovascular diseases since the genetic ablation of β-Arrestin2 resulted in an increase in saline intake and exacerbated BP.