Blood Pressure, Vascular Reactivity, and SOD Expression/Activity in Mas1 Receptor Knockout Rats in the Dahl Salt‐Sensitive Genetic Background

Abstract

Dahl salt‐sensitive (SS) rats are the most widely used rodent genetic model of human salt‐sensitive hypertension. Earlier studies have established the importance of impaired regulation of the renin gene in contributing to endothelial dysfunction in SS rats and the protective effect of low dose angiotensin II (ANG II) infusion in restoring endothelial function via the ANG II type1 receptor (AT1R) in the SS genetic background. Activation of the Mas1 receptor (Mas1R) for angiotensin (1‐7) [ANG (1‐7)] generally opposes ANG II‐mediated effects of AT1R activation. In Sprague‐Dawley rats fed high salt diet, binding of ANG (1‐7) to the Mas1R can activate NRF2 defenses and restore impaired endothelial function. The goal of the present study was to provide initial phenotyping of a Mas1R knockout (Mas1R KO) rat in the Dahl SS genetic background. Mas1R KO rats and wild type (WT) controls (12–15 weeks old) were maintained on a low salt (LS; 0.4% NaCl) or switched to a high salt (HS; 4% NaCl) diet for 3 days or 10 days. Arterial pressure measured via telemetry was similar in Mas1R KO rats (121±7 mmHg, n=3) and WT rats fed LS diet (124 mmHg, n=2) and increased in WT (138 mmHg, n=2) and Mas1R KO rats (132±5 mmHg, n=3) fed HS diet for 10 days. In rats fed LS diet, Mas1R KO eliminated vasodilator responses to ANG (1‐7) and AVE0991 (Mas receptor agonist) in middle cerebral arteries (MCA) and mesenteric resistance arteries (MRA) and reduced acetylcholine (ACh) reactivity in MCA. Because superoxide dismutase (SOD) enzymes contribute to antioxidant defense by catalyzing the dismutation of superoxide radicals and help to prevent diseases related to oxidative stress and endothelial dysfunction, we measured superoxide dismutase 1 (SOD1) and superoxide dismutase 2 (SOD2) activity in the liver of WT and Mas1R KO rats after 3 days of HS diet. High salt diet increased SOD1 activity (WT‐LS 1.04±0.16 U/ml vs WT‐HS 1.65±0.12 U/ml) and SOD2 activity (WT‐LS 0.76±0.03 U/ml vs WT‐HS 1.06±0.11 U/ml) in WT rats, but not in Mas1R KO rats. SOD1 and SOD2 mRNA expression (evaluated via RT‐PCR) tended to increase in WT rats fed HS diet vs. LS diet (1.3 – 1.8 fold change, p > 0.05). SOD1 mRNA expression was significantly higher in HS‐fed Mas1R KO rats vs. Mas1R KO rats fed LS diet (2.8 fold change, p = 0.01) and SOD2 mRNA tended to increase as well (1.7 fold change; p = 0.1). SOD1 and SOD2 protein expression measured by Western blot analysis was similar in WT and Mas1R KO rats fed either LS or HS diet. The present study using the Mas1 receptor knockout in the Dahl SS rat genetic background suggests that Mas1R activation by its agonists (AVE 0991) and ANG (1‐7) improves endothelial function and may provide novel therapeutic strategies for the treatment of low‐renin salt‐sensitive hypertension.Support or Funding InformationNIH #HL‐128242 and NIH #R21‐OD024781