Abstract P2030: DOCA-Salt Diminishes Brain RAS Activity In Parallel With Plasma And Renal RAS Activity - No Evidence For Selective Brain RAS Activation

Abstract

Deoxycorticosterone acetate (DOCA)-salt is suggested to increase blood pressure via selective upregulation of the brain renin-angiotensin system (RAS), while suppressing the circulating RAS. Yet, we have observed parallel downregulation of plasma and brain renin in mice. Here, we quantified brainstem angiotensinogen (AGT) and angiotensin (Ang) levels in rats exposed to DOCA (200mg; 60-day release) and 0.9% NaCl as drinking water for 7 weeks. To determine the contribution of AGT (liver vs. kidney/brain), Ang II type 1 receptors (AT1R) and blood pressure to tissue Ang II content, rats received vehicle, liver-targeted AGT siRNA (10 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, the latter fully normalizing blood pressure (n=3-9 per group). Plasma renin and AGT were determined by enzyme-kinetic assay, tissue AGT by western blotting, and Ang I and II by LC-MS/MS. Plasma renin, AGT, Ang I and II in rats not exposed to DOCA-salt were 24±8ng Ang I/mL per h, 731±51nM, 123±38pM and 109±43pM. AGT was present in liver, kidney and brainstem. Kidney Ang I and II were 540±135and 510±97fmol/g, while brainstem Ang I and II were undetectable in all and 50% of the rats, respectively (<6 and <12±4 fmol/g). DOCA-salt lowered plasma and renal Ang I and II by ≈90%, while brainstem Ang II became undetectable in 70% of the rats. AGT siRNA reduced plasma AGT by 97±1%, with similar reductions in the liver and kidney, while brain AGT was unaltered. Neither valsartan nor spironolactone affected AGT at any site. Spironolactone increased plasma renin, and hence plasma, renal and brain Ang I and II also rose modestly. Both siRNA and valsartan tended to further lower renal Ang levels, while neither drug affected plasma renin or Ang I and II in plasma and brain. In conclusion, DOCA-salt suppresses plasma, renal and brain Ang II in parallel. Renal Ang II is determined by hepatic AGT and relies on AT1R-mediated internalization. Although brain AGT is liver-independent, it is unaltered by DOCA-salt and does not permit selective brain RAS upregulation. The RAS upregulation induced by spironolactone, combined with its blood pressure-normalizing effect, argues against the (brain) RAS as a major blood pressure determinant in this model.