DOCA-SALT DIMINISHES BRAIN RAS ACTIVITY IN PARALLEL WITH PLASMA AND RENAL RAS ACTIVITY – NO EVIDENCE FOR SELECTIVE BRAIN RAS ACTIVATION

Abstract

Objective: Deoxycorticosterone acetate (DOCA)-salt is suggested to promote hypertension by selectively upregulating the brain renin-angiotensin system (RAS), while suppressing the circulating RAS. Yet, we previously observed parallel downregulation of plasma and brain renin in mice. Here, we quantified angiotensinogen (AGT) and angiotensin (Ang) in rat brainstems. Design and method: For 7 weeks, rats received DOCA (200 mg; 60-day release pellet) and saline as drinking water. The contribution of AGT (liver vs. kidney/brain), Ang II type 1 receptors (AT1R) and blood pressure to tissue Ang content was determined by treatment with vehicle, liver-targeted AGT siRNA (30 mg/kg fortnightly; s.c.), valsartan (31 mg/kg/day; s.c.) or spironolactone (80 mg/kg/day; s.c.) during the final 3 weeks (n = 7–8/group). Plasma renin and AGT were quantified by enzyme-kinetic assay, tissue AGT by western blotting, and Ang I and II by LC-MS/MS. Results: Plasma renin, AGT, Ang I and II in rats not exposed to DOCA-salt were 20 ± 4 ng Ang I/mL/h, 730 ± 37 nM, 140 ± 24 pM and 108 ± 24 pM. AGT was present in liver, kidney and brainstem. Kidney Ang I and II were 540 ± 135 and 510 ± 97 fmol/g, while brainstem Ang I and II were undetectable in all and 30% of the rats, respectively (LLOQ <6 fmol/g). DOCA-salt increased blood pressure by 19 ± 1 mmHg and lowered plasma and renal Ang I and II by ∼90%, while brainstem Ang II became undetectable in 70% of the rats. AGT siRNA lowered plasma AGT by 97 ± 0.3%, with similar reductions in the liver and kidney, while brain AGT was unaltered. Whereas spironolactone normalized blood pressure, it increased plasma renin, and plasma, renal and brain Ang I and II. siRNA and valsartan tended to further lower renal Ang, without affecting blood pressure, plasma renin or plasma and brain Ang I and II. Conclusions: DOCA-salt suppresses plasma, renal and brain Ang II in parallel. Renal Ang II depends on hepatic AGT and AT1R-mediated internalization. Brain AGT is liver-independent, but unaltered by DOCA-salt, thus not permitting selective brain RAS upregulation. The RAS upregulation during spironolactone, combined with its antihypertensive effect, argues against the (brain) RAS as a major blood pressure determinant in this model.