Abstract P331: Angiotensin-salt Hypertension Requires Ouabain-sensitive Na + Pumps

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Dietary salt is a major factor in the pathogenesis of essential hypertension (EH), but the underlying links are unresolved. Animal models indicate that angiotensin (Ang) II and high dietary salt (HS) are convergent signals that act via the brain to elevate blood pressure (BP). Low-dose sc Ang II+HS is a common model for EH. We tested the Na + pump ouabain binding site’s role in this model because it is crucial in some other hypertension models (e.g., ACTH and Nedd4-2-knockout +HS). Mice that express Na + pumps with a mutant, ouabain-resistant α2 catalytic subunit (α2 R/R ; cation transport is normal), and wild type (WT), ouabain sensitive controls (α2 S/S ) were studied. [80-90% of rodent artery myocyte Na + pumps are ouabain-resistant (α1 R/R ); only 10-20% are α2.] BP was measured by telemetry. First, 3 basal 24 hr BPs were recorded. Osmotic 4-week minipumps were then implanted sc in all mice to deliver vehicle (saline; Expt. #1,3), or 400 (Expt. #1,2) or 800 (Expt. #3) ng/kg/min Ang II; simultaneously, in Expt. #2, the diet was switched from 0.4% (standard) to 2% NaCl (HS). BPs were monitored every 3-4 days for up to 4 weeks. Also, in Expt. #2, on day 21, all mice received 2 ip injections, 4 hrs apart, of 10 mg/kg DigiFab, Fab fragments that immuno-neutralize ouabain, while BP was continuously monitored; on day 23, the mice received 2 ip injections of CroFab, anti-crotalus toxin (‘control’) Fab fragments. Results: 1. Basal mean BP (MBP) was 10±2 mm Hg higher in α2 R/R than in WT mice ( P <0.01; n =21 & 29; ANOVA). 2. In WT mice, 400 ng/kg/min sc Ang II and Ang II+HS raised MBP by 15±1 and 34±1 mm Hg, respectively ( P <0.01; n =7-8; ANOVA). 3. The MPB elevation in Ang II+HS α2 R/R (17±2 mm Hg) was only half that in WT mice ( P <0.01; n =7 each; ANOVA). 4. DigiFab rapidly (<1 hr) reduced MBP by 14±2 mm Hg in Ang II+HS hypertensive WT mice ( P <0.001; n =7; T-test), but not in α2 R/R mice ( P <0.01; n =7 each; ANOVA); CroFab did not lower MBP in either strain. 5. 800 ng/kg/min sc Ang II elevated systolic BP by 55±3 mm Hg in WT mice, but by only 37±3 mm Hg in α2 R/R mice ( P <0.05; n =3-5; ANOVA). Conclusions: Ouabain-sensitive α2 Na + pumps and their endogenous ligand are both required for full expression of low-dose Ang II-salt hypertension. Ouabain-sensitive α2 pumps apparently also contribute to high-dose Ang II-hypertension.